How to Diagnose and Repair Your Air Conditioner (A/C) Capacitor

Updated on April 26, 2018
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Dan has been in the HVAC industry for 22 years with experience ranging from installation and service to sales and distribution.

What's Wrong With Your Air Conditioner?

A capacitor usually resembles a tin can or 9-volt battery.
A capacitor usually resembles a tin can or 9-volt battery. | Source

Capacitors Are a Common Cause of Air Conditioning Breakdowns

Luckily, you can often replace them yourself.

So it's a hot day in the summer sun. The family is coming over this weekend and you're very busy making all the necessary arrangements, when suddenly the A/C quits working. Perfect timing, right?

Well, before you call the local HVAC technician to come fix the unit, and re-allocate the money you were going to spend on burgers, take a quick look. Perhaps you're about to luck out by making a simple repair that will only cost you a few dollars and take very little time. It's also helpful to find out whether your air conditioner is still under warranty, in case you want to replace it later on.

If you need to fix it right away, you won't need any specialty tools, and you may not have to rearrange your entire day. Just a few minutes, a couple of tools you likely have around the house, and these instructions could save you a significant amount of money while keeping your family gathering right on track.

What Is a Capacitor?

Capacitors are small cylindrical objects that store energy. They either send a jolt to start a motor or send jolts to keep a motor running. They work with the compressor, the blower motor, and the outside fan in your air conditioner.

Checking Your Air Conditioning Capacitor

A voltmeter, if you have one, can tell you if you have blown a capacitor, but it’s even simpler to find out just by watching and listening. Take a walk outside to your condensing unit, and look and listen for the following:

  1. Do you hear any humming?
  2. Do you see the fan spinning?

If the A/C is humming but the fan is not running, you may have a capacitor problem.

A Simple Trick to Test if the Capacitor Is Working

If the A/C is humming but the fan is not turning, find yourself a long skinny stick. Gently slide the stick through the fan grate and give one of the fan blades a gentle push, to see if the fan will spin. If the fan takes off on its own and keeps going, you very likely have a bad start capacitor.

You see, the capacitor is there to give a boost to the fan motor upon startup. A capacitor stores power in a roll of electrically charged sheets of material.

When the capacitor is called to action, it is supposed to release its energy and give the fan a sort of electrical kick in the pants. If the capacitor is shot, the fan can't quite get going from just the 120 volts the motor supplies to it. You and your stick just took over the job of the start capacitor.

There are a few things that could have caused your capacitor to blow. The heat of summer plus motor heat could have proven to be too much for the part, or it could be something else.

Below I'll go over how to fix this problem yourself.

Does this sound like what's going on with your A/C?

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Quick Overview: How to Replace an A/C Capacitor Yourself

Step
Detail
1. Turn off the power to the unit at the disconnect or breaker panel.
Do not proceed if you do not know how to do this.
2. Find and inspect the capacitor.
Remove the service panel, locate the start capacitor, and check to see if it's mishapen.
3. Discharge the power of the capacitor.
Be very careful in this step — watch the video below for details.
4. Dismount the old capacitor.
It should be simple to unscrew the metal band holding it in.
5. Note down how the wires connect.
Do this before you remove them!
6. Disconnect the wires.
You can remove them with needle-nosed pliers.
7. Choose a replacement.
Know the micro-farads (μF) and the voltage rating, or the make and model of A/C
8. Buy a replacement and attach.
Check your local contractor supply store.
See below for more detailed information and pictures.

1. Start by Turning Off the Power

First of all make sure you know how to turn off power to your air conditioner. Don’t proceed if you do not.

  • Turn off the power to the unit at the disconnect or breaker panel, which should be mounted on the outside of the house within a few feet of the outdoor condensing unit.

The disconnect box for the air conditioner.  The cover opens easily.
The disconnect box for the air conditioner. The cover opens easily. | Source
On this particular disconnect, pulling the handle cuts the power and exposes the fuses.
On this particular disconnect, pulling the handle cuts the power and exposes the fuses. | Source

2. Finding and Inspecting the Capacitor

After you have turned off the power at the disconnect:

  1. Remove the service panel on the A/C unit itself.
  2. Locate the start capacitor. (It's most likely silver, round or oval, and with multiple prongs on the top for wire connections.)
  3. Look at the capacitor surface where the prongs are attached, and ask yourself: does this surface look raised or domed?

One tell-tale sign that a capacitor is shot is its shape. When a capacitor blows, at least 95% of the time its top will be pushed up or swollen, somewhat resembling a pop can that has been dropped and is ready to explode when given the chance. Is this what you see? If so, this is good news, and we'll have you back up and running in no time.

It may not be pretty, but there's my capacitor.
It may not be pretty, but there's my capacitor. | Source

3. Discharging the Power in the Capacitor

You've already shut off power to the air conditioner, but now you will have to discharge the power in the capacitor.

WARNING: As I mentioned, a capacitor stores power. That has not changed because you've shut off the flow of electric current. The capacitor may still have power ready to fire. Touching two of the terminals at the same time with your hand will discharge this power and make for a shocking experience. Throwing away a capacitor that hasn't been discharged could cause a fire in your trash can. Before you continue, discharge your capacitor by placing an insulated-handle screwdriver across the terminals, as shown in the video below.

Video: Discharging a Capacitor

4. Dismounting the Old Capacitor

Now that your old capacitor has been discharged, you can remove it. This is very simple. The capacitor is likely mounted to the unit by a metal band that has only one screw to remove. Remove that screw and the capacitor should come loose from the unit itself.

One screw and it's out.
One screw and it's out. | Source

5. Noting Down How the Wires Connect

Before you remove the wires from the old capacitor, be sure to make a diagram or label showing what wire goes where.

Different colored wires go to different terminals.  This capacitor is good, so the top is flat, but if it were broken the area around the terminals would likely be raised like a shaken pop can.
Different colored wires go to different terminals. This capacitor is good, so the top is flat, but if it were broken the area around the terminals would likely be raised like a shaken pop can. | Source
You can draw a picture showing where the different colored wires will connect to your replacement capacitor.
You can draw a picture showing where the different colored wires will connect to your replacement capacitor.

6. Disconnecting the Old Capacitor

Once you're sure where the wires will connect to the new capacitor, you can remove the wires using a simple pair of needle-nosed pliers. If the wires are tight, try not to just yank on them; use a rocking motion while pulling slowly. This will help keep you from touching another terminal, or possibly having the pliers slip and hit you in the face. Don't laugh, I've watched it happen.

That's it. Now all you need to do is obtain the right replacement part and re-install it just as you removed this one.

7. Choosing a Replacement

There are a couple of things you'll want to know when shopping for your new capacitor: the micro-farads (μF) and the voltage rating. The shape and size of the capacitor aren't really important as they can vary and still do the job. Even your mounting bracket will probably bend to accommodate a part of a different shape. Just know that you have to match the micro-farad number exactly. The voltage rating does not have to be identical, as it shows the amount of voltage the capacitor can see, not what it has to see; this means that if you need to you can use a capacitor with a slightly higher voltage rating than what you have now.

Your μF and voltage will be marked on your capacitor and will likely read something similar to 35/5 μF and 370V. If they are not written down, write down the make and model of your air conditioning unit, and use that information at the store or online to find the correct replacement part.

Lastly, brand is not important here. A capacitor is a pretty universal part, and should be available at your local contractor supply company, though maybe not at a Home Depot or Lowe's.

A capacitor for a residential-sized unit should be relatively cheap, and you may consider buying a second one for backup while you are there, along with a couple of spare time-delay fuses (but be sure to buy the right size fuse). In the heat of the summer, blown capacitors and fuses are a very common cause of air conditioner breakdowns. If you suspect fuses are the problem, it is easy to learn how to replace air conditioning fuses.

Air Conditioning Maintenance Tips

I hope this was the answer to your A/C problem and that you were able to obtain and replace the part without any hang up for your family get-together.

The heat of the summer sun, added to the heat hard-working motors normally generate, can be tough on our air conditioners, because hot electrical components break down more easily. So it's not surprising a part may fail on a hot day when you need it the most.

Keeping up on your A/C maintenance can help prevent these types of breakdowns. Keeping your air conditioner's coils clean and your air filter cleaned or changed when needed can keep the running temperature of your unit down, thus helping to keep your own temperature down when the summer comes calling.

For those with window units, when winter time comes around, you might want to remove the unit and store it somewhere to protect it from frost, dirt, and debris.

Thanks for stopping by, and again, I hope this helped you and saved you money.


Questions & Answers

© 2012 Dan Robbins

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    • Cre8tor profile image
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      Dan Robbins 32 hours ago from Ohio

      katostein - I'm not sure what it was doing in the first place so it would be hard for me to say what should be different. If replacing the capacitor didn't work then you may have a different issue. Keep in mind the skinny line shouldn't be cool at all. It should be warm. The larger one should be cool or even sweating under certain conditions. If these are not the case then you may have a refrigerant pressure issue and that is not something you can try and remedy yourself.

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      katostein 2 days ago

      hello i have an older Carrier unit, just replaced the capacitor and a week later it is acting the same way. the outside line is barely cool to touch.

      any ideas??

      thanks!!

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      Dan Robbins 4 days ago from Ohio

      Robin - Make sure you try to spin the fan both ways with the stick to ensure you're going in the right direction or it won't spin. Otherwise, you may have a bad fan motor, perhaps bad contact in the contactor (make sure the button/plunger is pulled in all the way...you can push it in with a stick too to see if that is making good contact.) Make sure your fuses aren't blown or the breaker is tripped so that you know you have power because the hum could just be the contactor pulling in that is getting power from the furnace, not the a/c power lines so you can have power from one and not the other. Hope this helps give you a few more things to check and see if you can get it working. Beyond that you'd really need to call a tech out to run tests. Thanks for reading.

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      Robin 4 days ago

      We noticed the fan in the outside A/C unit isn't turning, and there's a very audible hum coming from the unit, as if it's trying. The air is blowing inside, can't tell if it's cold, but when we give the fan a push with a stick, it doesn't keep turning. (It stops)

      Any ideas??

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      Dan Robbins 11 days ago from Ohio

      First, I'll guess capacitor but that's just a hunch. The issue is, why does it keep blowing. I'm assuming they aren't there all day when they fix it and they are just fixing the immediate issue but the fact that this keeps happening, they should be looking for the "why". You should be able to verify your warranty through whomever sells that brand of equipment in your area. Call and give them your serial number (maybe model too) and they should be able to tell you.

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      Mark 13 days ago

      Every year since I’ve bought the house ( 4yrs) my air goes out st the beginning of summer. It’s been under Warrenty but I don’t think it is anymore. I don’t know what they do when they come out. But it’s symptoms are: it hums and doesn’t start and then I hear a noise like a poof. And then there’s no noise. Any help would greatly be appreciated.

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      Dan Robbins 13 days ago from Ohio

      There are capacitors in both. The one inside is for the fan in the air handler/furnace and the one outside is for the heat pump.

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      Dan Robbins 5 weeks ago from Ohio

      Khurram - The problem may be in the motor itself. Perhaps that's why the capacitor went bad in the beginning. You may have to look into a motor but in my experience, window units aren't easy to find parts for and take time to install...be sure to weigh replacing the motor vs. getting a new unit that would have a warranty and likely be more efficient.

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      Khurram 5 weeks ago

      Sir i replaced ac compaster window ac o general 2ton but still fan speed is sloe

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      Dan Robbins 5 weeks ago from Ohio

      Sunil - It sounds as if it's short cycling usually meaning the unit is oversized and satisfying the thermostat too fast. Like blowing cold air directly at the stat so it shut off quickly though the home never truly/thoroughly got to cool. Running the fan in "on" mode may help slow that down a bit. I should also say if temperatures are extreme then it could just be that as well.

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      sunil 5 weeks ago

      my a/c compressor turns off after every 6.5 mins and again restarts after 15 mins to run again for 6.5 mins

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      Dan Robbins 7 weeks ago from Ohio

      That should not be the case. No.

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      Earl 7 weeks ago

      could the outside temp make the compressor too hot before I turn it on it seems to work fine set at 74

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      Dan Robbins 8 weeks ago from Ohio

      Earl - There are a few possible cause here but most require the services of a technician. Compressor repairs aren't something I can walk you through. Thanks for reading and commenting.

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      Dan Robbins 2 months ago from Ohio

      Michele, A start kit won't hurt and you can check the capacitor for proper sizing by getting the model number and checking with the local distributor for what should be in it.

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      Michele 2 months ago

      Since the A/C capacitor was replaced by a repair company whenever my A/C comes on some of my lights dim in the house. I'm thinking it's because the A/C repair tech used the wrong replacement capacitor. He is telling me I need a start kit.

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      Dan Robbins 3 months ago from Ohio

      It very well could be and because they are typically very inexpensive can't hurt to try.

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      smalz 3 months ago

      My compressor does not come on at all. No fan spinning or humming. Could this be the dual run capacitor? I have a york model H1RE030S06D.

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      Dan Robbins 3 months ago from Ohio

      I don't know for sure as makes and models vary and LG is not a brand I'm familiar with. It should however be on the capacitor you're removing. Thanks for reading.

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      Deepak 3 months ago

      I need one capacitor for LG 1.5 ton split ac, kindly suggest right make and model.

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      Dan Robbins 4 months ago from Ohio

      Robert - Sounds like you have a short somewhere if it's tripping the breaker. Sorry I can't help more based on this info.

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      Robert Lovelace 4 months ago

      Unit turns on and trips breaker stew minutes later?

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      Dan Robbins 5 months ago from Ohio

      Mark, Thanks for sharing your results. Hope I was of some help to you.

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      Mark GG 5 months ago

      Dan - thanks for your quick response!

      After more research, I have now discovered that my unit does not have a "start kit". (Apparently, manufacturers stopped putting them in a/c compressor units to save on cost!)

      That's why I only have the one (dual run) capacitor, for running only.

      I have now ordered a "hard start kit", which should both reduce the amps required to start the compressor (the LRA value), but also extend its life.

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      Dan Robbins 5 months ago from Ohio

      Mark GG - That's what's referred to as a dual capacitor. It's used for both the compressor and fan and they share the common.

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      Mark GG 5 months ago

      This is a great article, Dan! Very clear and concise.

      Looking at the interior of my a/c's compressor/fan unit, I have noticed that it only has ONE run capacitor, with a dual 35+5 rating (i.e. 35 for the compressor and 5 the fan).

      I don't see a start capacitor anywhere in the unit.

      Is that possible?

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      Sajjad Rasheed 7 months ago

      Hi Dan

      I have purchased second hand Vertical Air condition of about .75 ton , but after few days it is tripping again and again, when ever the compressor starts after few minutes of Fan running it goes trip showing an error " E C ".

      Thank you in advance for helping.

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      Dan Robbins 7 months ago from Ohio

      Billy - It would be hard for me to say from here but it sounds like some sort of overload or limit is tripping and time allows it to reset. Which and why are questions you'd need a tech to trouble shoot. Thanks for reading.

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      Billy 7 months ago

      My a/c runs and cools fine, however when it reaches it's desired temp it won't come back on. The blower will but not the compressor. If I want until the next day it will run perfect until it shuts off and won't come again until the next day what could this be?

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      Mark 7 months ago

      This worked perfectly. My fan was very hot, humming, and not moving. I was occasionally able to get it running, but only for a short time. This worked perfectly and saved me about $600.

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      Dan Robbins 8 months ago from Ohio

      Melissa Franklin - I wish I could truly troubleshoot from here but I cannot. Something like this requires a fair amount of circuit testing and timing to see what's going on. It kind of sounds like the thermal overload on the fan or compressor or both have tripped. The cold water is what perhaps cooled the fan enough to come on but maybe not the compressor which you'll want to be careful because a drastic temp change could cause things to separate or crack and then it's game over. I don't think this is really a do it yourself kind of fix so you should consider calling a technician if it persists. Sometimes, it could just be extreme conditions and not be a problem when the weather levels off. Sorry if that's not a great help but thank you for reading.

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      Melissa Franklin 8 months ago

      So I'm really confused here...im a single mom and I let my ac temp down lower then I usually do...and ended up forgetting to turn the air up before leaving for work...my kids and I came home around 6 pm from.work and school ac A/V was running finr...then about an hour later we noticed it was starting to get warm in the house....the vents where blowing inside but not cold and I went out back to check the unit and it wasn't spinning...you could hear that it wanted to turn on but wouldn't start....and it was hot to the touch....so I was told to let the hose run on it to cool it down amd then to try to manually start it...so I did and the fan started spinning...but it's not cooling the house....i live in Florida with 2 small kids...could the capacitor be this issue for this...(I truly hope so...)

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      Dan Robbins 8 months ago from Ohio

      MccG - While I can't confirm or deny what the tech says the issue was, if there is a recurring issue, a tech should always look for an underlying cause. Parts done typically fail multiple times in a short period unless there is an underlying problem or extreme conditions. Sorry I can't offer more about a resolution but hopefully it will help a bit. Thanks for reading.

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      Dan Robbins 8 months ago from Ohio

      Matt - Great to hear! Really glad I was able to help if only a little. Best wishes.

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      Matt 8 months ago

      Was able to diagnose and confirm it was the capacitor with your article. A $20 part and it's fixed! I even bought a spare. Thanks so much!

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      MccG 8 months ago

      Dan I have had two capacitors replaced by my HVAC company over the past six months. However, after reading your article, I'm not sure that the capacitor has been the problem. The notes from the last visit state that the wire connecting to the common terminal was blown off and melted. The fan was running, but the unit wasn't cooling and the capacitor was not deformed. So, is this a capacitor issue?

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      Dan Robbins 8 months ago from Ohio

      Brian Ehlers - I would be suspecting the contactor based on this bit of information. I can't say that's it for sure but it is what I would check first if you told me this. I would try and manually push in the contactor with a stick or something non-conductive and see if the unit kicks on. This is 230v circuit so be careful and if you think this is it and chose to do the repair yourself, be sure that all the power is off. I don't recommend you trying this if you are not fully confident in your electrical skills. Thanks for reading.

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      Brian Ehlers 8 months ago

      Hi! My ac heat pump is not working. I tripped breakers. Thats not it. Fan is blowing warm air thru the vents. When switching the thermostat from off to cool the outside unit makes a clicking sound like it wants to turn on. However, the fan and compressor do not fire up. Do you think this is a capacitor issue?

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      Dan Robbins 8 months ago from Ohio

      Clint - I don't know of motors working when they're bad even when they are manually started. I suppose the new cap could be defective out of the box...wouldn't be the first time though it's not real common. I suppose I'd try that first since it's inexpensive but it's hard for me to say without being able to run further tests myself. Thanks for reading!

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      Clint Fuhs 8 months ago

      Hi Dan,

      Thanks for this article. I followed your directions and replaced a capacitor on an Trane AC that was not cooling. The old capacitor was mushroomed and was reading way below spec on my meter. I replaced it with a new one from amazon but before doing so, I checked it with my meter. I got the appropriate reading between C - fan and C - Herm. Now, the compressor starts but the fan won't kick on unless I spin it manually. Should I try another capacitor? Or can a fan motor be bad and still operate if the fan is turned manually?

      Thanks!

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      Dan Robbins 8 months ago from Ohio

      Pete - Camper units are a different animal. I'm not familiar enough with these to offer any real advice. I wouldn't be sure how cold air could be felt if there was no fan but again, that could just be my lack of experience with these. Sorry but thank you for reading and commenting.

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      PETE 8 months ago

      hi DAN IM NEW AT THIS, BUT HERE I GO. MY A/C UNIT IS UNDER A PARK MODEL CAMPER , MY WIFE TURNED IT ON AND CAN FEEL COLD AIR BUT IT DONT SEEM TO BE BLOWING THRU THE VENTS,ITS TOUGH TO GET UNDER THERE DO YOU THINK IT JUST MAY BE MY FAN NOT COMING ON? THANKS

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      Dan Robbins 8 months ago from Ohio

      GJ - I too am a bit confused and this is what happens when trying to imagine your set up over the net. Not your fault but it is very difficult. That said, if you've cut power to the a/c, you should be fine. The only voltage from the furnace would be the 24v call for air. That all said, it sounds like you have a rather unique set up or that I'm not understanding exactly what you have. Maybe it's just terminology...I don't know but I don't want to advise any further not knowing for sure what you're dealing with and being able to run voltage tests of my own. Sorry I can't be of more help but this is difficult over the net.

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      Dan Robbins 8 months ago from Ohio

      Kevin - Perhaps you've missed the parts where I've consistently stated not to work on things "you" aren't comfortable with and to be safe and turn off all power supplies...etc... In 5 plus years I've not heard of anyone being hurt by anything I've stated nor have I been careless to advise anyone to do anything that requires a license or specialty equipment. But I suppose you're a contractor who sees me as ruining business for you. I prefer to see me helping people perform the most basic of repairs and keep from being gouged over something as simple as a capacitor repair when they're trying to keep food on the table and stay cool in the process. Perhaps you'd like to point out where I've put someone in harms way so I can remove such statements. Surely that isn't my goal here. Thanks for your opinion however and I'm sorry if I've cut into your action by helping people who can't afford $75-$125 service calls plus repair.

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      G. J. 8 months ago

      Hi Dan,

      Thanks for responding and for your feedback. I looked at the breaker box, and there are 2 additional switches on the box that say "Heater." So I am not sure if these are the ones that you are referring to, so just let me know if you think that I need to switch these off in addition to the 2 that say "AC." Also, if I do switch the ones marked "Heater" off, will I then need to re-light the heater when I'm done?

      Also, regarding the Switch at the A/C unit, it is just a lever, so I don't think that is the Handle type that needs to be pulled. I know that when I put it to the off position, the unit turns off.

      Finally, I think that I may have confused you with my initial post about the reading that I was getting. I had not removed the Capacitor, I had just turned everything off and made an attempt to discharge the Capacitor using a screwdriver. Then when I used the detector, I got a reading. However, as I mentioned, when I went back a couple of weeks later, the detector did not pick up a reading , so that is what made me wonder if the Capacitor may have discharged over that time, if my attempt at discharging was not successful. However, when you mentioned that it may have been a reading from the Furnace, I was wondering if that is something that I need to disconnect as well, or am I good with shutting off the service box and A/C switches at the main panel in the garage?

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      Dan Robbins 8 months ago from Ohio

      Andrew - There are far too many possibilities for me to say anything for sure. Low/no efrigerant? Plugged filter or coils? Bad compressor? The only thing a do-it-yourselfer is really equipped to check would be a dirty filter and/or maybe a dirty coil depending on your set up. Sorry if that's not much help but thank you for reading.

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      Andrew 8 months ago

      So I had a similar issue and I replaced the capacitor and motor and it runs fine but there is only warm air coming out of my vents now. Any suggestions?

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      Dan Robbins 8 months ago from Ohio

      GJ - I'm still a bit confused on the capacitor part where you had a wire reading voltage when the power was off and the capacitor was out but I can say, you should have 4 breakers for 2 systems that have a/c on each furnace. 1 breaker per furnace (usually a single pole 15 or 20 amp for furnaces) and 1 breaker for the a/c. (usually a 2 pole breaker...20,30,40,50, amp). As for the disconnect, if you have a lever that you switch off then you won't be able to pull anything out except for the fuses which I wouldn't do unless they're bad. Just make sure you're switched off. However if you don't have a lever and there is a handle, it may be tight but you should be able to pull it. If it's marked "off/on" that just means when it's pulled out and flipped over, it's "off/on". Whichever word you can read without doing a handstand is what position it's in. Sorry if I'm not much help. There are a lot of things that can happen in this business and it makes it hard to diagnose via the net. Thanks for coming back and adding to the conversation though. I'll offer what I can when I can.

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      G. J. 8 months ago

      Hi Dan,

      Thanks so much for your prompt reply to my question below. I should have also mentioned that initially, I had cut the power to the unit from both the service box and the circuit breaker in the garage. We have 2 units, so I only turned off the service box to the unit in question, but of course the circuit breaker box in the garage controls both units. So I'm not sure if this additional info helps in answering my earlier question. Also, if the voltage is indeed coming from the furnace, do I need to do any additional unplugging, or am I safe with the disconnects that I described?

      Also, I have noticed that in many of the videos, the service box shut off switch pulls out. However, mine seems only to turn on and off. It does not seem to pull out, but I did not want to tug on it too hard as to avoid doing any damage to it. Our units are somewhat older, as I think that they could possibly be the original units, and the house was built in the late 90's. So any feedback you can give me on my questions/concerns would be greatly appreciated.

      Thanks again.

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      Dan Robbins 8 months ago from Ohio

      Roger D - Though I can't tell you what the cause is, the only thing you should hear in the lines is refrigerant rushing back and forth from the indoor to the outdoor. If the drain line is vibrating, then I'm thinking it's coming from the indoor unit, not the outdoor and if it's shaking the drain line, it must be pretty bad. If it's inside, it has to be the fan. There is nothing else in there moving with enough force to vibrate this badly. When was the last time you have the furnace cleaned? Meaning they took out the motor and wheel and cleaned both and checked the balance? Only cheap thing I could maybe recommend would be if you could slide some thin rubber padding under the bottom of the unit to perhaps absorb some of this vibration. Not sure it will be enough but it should help a bit if I'm right. Thanks for reading.

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      Roger D 8 months ago

      inside the house, the sound is of humming. The AC has worked fine - no leaks, cools properly etc. I have had it serviced but every time the service person chalks the noise to age and recommended a new AC w/o any investigation. It could be just age but I'd welcome suggestions things I can check for myself.

      I followed the two lines (thin copper line and the larger/covered in black line) running between outdoor and indoor AC units. If I put my ear next to the larger line, I can clearly hear the humming sound along its length as I move from the outdoor AC unit to the indoor condenser unit. I can also feel vibrations/tremors on this larger line and feel vibration where the lines come in and the discharge water line comes out

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      Dan Robbins 8 months ago from Ohio

      John Carr - Thank you much! Glad I could help. And if I'm in the Bay area, I will certainly take you up on that. Would love to see the west coast...never quite made it all the way there.

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      Dan Robbins 8 months ago from Ohio

      Michael Thompson - Weird that only one fuse blew but if you've checked and they are okay, then the next place I would look is the contactor or capacitor. If it's neither of those then it may be time to call a tech. You should have 24v coming from the furnace to the contactor. You can push the contactor in with a stick and see if it fires. If so, that's likely the issue. Please turn of the power if the contactor is bad and you decide to replace it yourself. Thanks for reading.

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      Dan Robbins 8 months ago from Ohio

      Pritam - That's possible but since the unit is so new, you should be under warranty and let a service tech figure out your issue since there could be other problems. Thanks for reading.

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      John Carr 8 months ago

      Hi Dan,

      I read your column after our a/c failed yesterday during a heat-wave here in SF Bay Area. 110+ both yesterday and today. I ordered a new capacitor on Amazon late last night after researching on your site, they delivered it this morning, cost $9.60. (This happened some years back and it cost $300.00) Anyway, we're back up and running but couldn't have done it without your help. If you're ever in the area the beer is on me!

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      Michael Thompson 8 months ago

      Hey dan have been reading your advice and hope you can help. My a/c has stopped working. I checked the fuses in the disconnect box and found a bad fuse. I replaced the fuse turned the power back on but still not working. So I pulled the fuses back out to see if maybe it blew another fuse. Fuse still ok. But a/c still not working. Any help will be greatly appreciated

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      Pritam 8 months ago

      Hi Dan,

      Thanks for the above concise & informative article. I am currently facing a problem with my inverter ac. It was working fine for 2.5yrs until recently it is working abnormally. It is very faintly cooling and the compressor seems to be not taking start. The outdoor unit fan is blowing very slow and when checked with tong tester-it is showing 4amps , and 230V supplyalthough the rating is 6.5amps. The temparature is not going below 30C. The error code at the remote controller is showing U2 error-i.e. Insufficient supply voltage, although supply voltage is normal.Can it be a outdoor unit capacitor problem??

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      Dan Robbins 9 months ago from Ohio

      G.J. - I'm not exactly sure what happened here but I can say if you shut down the main power to the unit then the only voltage reading that would/should be available would be 24v coming from the furnace. Thanks for reading.

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      G. J. 9 months ago

      Very nice article, but I do have a question for you. I disconnected and discharged my capacitor, but did not work on it immediately, as I was still getting a voltage reading from one of the wires. Since I was in no particular hurry to get the job done, I left the unit disconnected and then went back a couple of weeks later, and this time I did not register anything. I was wondering if the Capacitor may have discharged itself over time? Do you know if this might be what happened?

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      Dan Robbins 9 months ago from Ohio

      Michelle - If you can prepare to do so then I am of the mindset to do so before I have to than to do so when I HAVE to. Your unit is likely an R22 system which means any major repair that will be needed will far exceed it's worth and yes, I would rather replace it than to throw money at an obsolete unit that uses and obsolete refrigerant. Your repair costs on a major repair would likely be close to half if not more of a new unit install and to me, that's when it's time to replace. That said, summer is coming to an end and perhaps the best plan would be to prepare for next summer and get it done in the spring so you can reap the benefits of lower energy bills all summer and start recouping your money as fast as possible. You'll have to change the indoor coil and outdoor coil if in fact it is an R22 unit and you should strongly consider doing the furnace at the same time if possible since it's very easy for a tech to do so while doing the a/c at the same time. Hope this helps and best of luck. Thanks for reading.

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      Michelle Benavides 9 months ago

      My a/c went out this weekend and I had a technician come and check it out. He changed what he called the "starter" but said to replace the unit soon because the compressor was extremely hot. The unit was installed in 1989 but other than taking a bit longer to cool the house down it runs well. Should I spend the money to replace it?

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      Dan Robbins 9 months ago from Ohio

      jacqueline - If these things didn't work then perhaps it's time to call a technician who could run some tests and see what the issue is. Thanks for reading.

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      jacqueline 9 months ago

      change capacitor and fan motor ac still wont start sometime it start when I give it a spin with a stick the start up run about 2to 3 minute then it cut off

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      Yalonda 9 months ago

      I replaced the capicitor that is connected inside and attached to the fan instead of the one outside as you show. It worked overnight, but when I woke up it was off. I turned the air on and it is back to humming, but wont start without a push on the blower fan. My fan outside on the ac unit works. Any suggestions?

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      Abdelsalam Said 9 months ago

      what are the causes of capacitro failure & how can check the hermetic compressor winding to be sure if ok or not?

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      Dan Robbins 9 months ago from Ohio

      Gerald - That's a tough one. I've never had to change mine in 12 years. I know others who've had to do so a few times in the same timeframe. Often it's a matter of how hot and hard the unit is working (so FL is I'm sure a bit harder on components than up north). Proper maintenance helps keep things running efficiently, keeping amp draws and heat down but I don't have a real answer to the lifespan of a cap. I can say that if you're blowing caps on a regular basis then there is almost certainly an underlying issue causing that to happen. Thanks for reading. Hope that's of some help to you.

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      Dan Robbins 9 months ago from Ohio

      Jacqueline - It sounds like a short circuit. Either the transformer, board, or motor. Wish I could say which but it must be in the furnace to make the house smell and those are the most likely things to short and stink. It's possible (not likely to smell enough to go through the whole house) you've blown a 3 amp fuse on the circuit board. Doesn't hurt to check since it's easy to see and check with the eye. Sorry I can't really help more without doing electrical tests. Thanks for reading.

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      Jacqueline 9 months ago

      Hey last night the air conditioner was working good until like 2 am we smell like something was burning so we get up and the smell was coming from the air vents I turned everything off quickly and this morning I try to turn it on but it won't turn on

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      Gerald Jacobs 9 months ago

      I live in Florida. What kind of life span can I expect from a capacitor?

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      Dan Robbins 9 months ago from Ohio

      Gene - I don't think so. A fused disconnect should prevent one from damaging the other. There may be a scenario but if there is, I've never experienced it. Thanks for reading.

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      Gene Fuentes 9 months ago

      My AC unit won't start so maybe the capacitor needs to be replaced, I thought, however I discovered that the breaker at the breaker box did not have any power. Called an electrician to first replace the breaker ($$$) and the unit did not start. The electrician inspected the AC unit finding that the capacitor was not working and suggested that maybe the failing capacitor caused the breaker to fail. Is that possible?

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      Dan Robbins 9 months ago from Ohio

      Craig Stein - Glad to hear I was able to help and that the motor shop was able to give you an option. Thanks for sharing your experience and reading!

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      Dan Robbins 9 months ago from Ohio

      Larry Grissom - Sorry it was a hair late but thanks for reading and wish I could've helped in time.

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      Dan Robbins 9 months ago from Ohio

      Andre - Awesome! and thank you for the feedback!

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      Andre 9 months ago

      Very good, clear article. It worked with my problem, a lot of money saved. Thanks.

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      Elizabeth 9 months ago

      Hello again. My a/c unit was not blowing out cold air and heating pump was acting weird would start then stop. I found that the contactor was burnt. I replaced the contactor, capacitor and strip off the wire tips to the contactor and capacitor and put new ones. By golly it definitely work like a charm. Now my A/C is blowing cold air like it should. This website is a plus for do-it-yourself and saves alot of $$$$. Thank you so much.

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      Larry Grissom 9 months ago

      Dan, thanks for the concise, informative article. Had I read it last night I could have saved money plus had cooling overnight. My symptoms were precisely what you described, except that my capacitor had no obvious deformation.

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      Craig Stein 9 months ago

      thanks so much for this article, AC died last night and due to the troubleshooting steps listed here it was definitely the capacitor. Replaced the capacitor and it is running like a top now. I should mention that the electrical motor repair place i went to did not have a single capacitor but was able to provide two capacitors linked together to provide the microfarads my compressor and fan needed. First capacitor was 35 mfd and 5 mfd and the second was 10 mfd which was linked through the common and the compressor connections. The first capacitor also was 5 mfd for the fan which was sufficient.

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      Dan Robbins 10 months ago from Ohio

      Dominic - Your tech (I have to assume) would've made sure the capacitor wasn't the issue when installing the new hard start kit. I often am skeptical when a tech suggests a new unit just because unfortunately there are a lot of guys who will do so when not knowing what else to do. That said, in the case, I may agree. One, it sounds like he's tried to save the unit first. Two, throwing money at an R22 system is a bad idea. The refrigerant is obsolete and repairs to an R22 compressor can cost hundreds just in the refrigerant to be put into the system. In reality, the refrigerant alone could end up costing you between $400-600 dollars. That wouldn't include the $400-500 (or more) for the compressor...both of which are his cost...not yours that will likely be marked up and then add labor which is intensive to replace a compressor and after all that, you still have an old inefficient unit that could and likely will need repairs again in the future and has no warranty. To further that, since the EPA has done everything in it's power to eliminate R22 units, parts have become more and more hard to find and costly. I don't mean to be doom and gloom but want you to fully understand what you're facing. Replacing the unit doesn't mean you have to replace the furnace however it may be a good time to consider it if it's older too because the cost to do so while doing the a/c should save you in the long run. He will have to replace the evaporator coil inside along with the outside unit since the new R410a systems cannot work with the old R22 indoor coils. I hope this helps. It may not be what you want to hear but should prepare you for estimates you may get and know what they are saying is true. Thanks for reading and commenting.

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      Dominic 10 months ago

      Hi Dan,

      I hope you can help. My A/C unit compressor is not kicking on. the fan outside is blowing and every now and the i hear a hum like the compressor is trying to start, but it does not. Could this be a capacitor issue?

      I did have an A/C guy look at it and he said he hooked up a new booster to the capacitor to start it (I already had one on the unit for 2 years). Could the capacitor be bad? The A/C guy said my compressor is bad and wants to sell me a whole new unit. I have a 10 year old 4 ton R22 unit right now.

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      Dan Robbins 10 months ago from Ohio

      trazor - If you've not yet replaced the capacitor in this video, then you'll have to wait for it to arrive. Remember the stick method is not a repair, only a DIY test to see if the capacitor is likely bad. Now, if you have replaced it and it still doing this then I'd say you may have an underlying problem. It sounds like (if I'm not mistaken that the compressor is still running and the fan looks to free spin so I would be thinking capacitor however there is the chance that there is something else going on in the circuit. I hope this helps a bit. Thank you for reading and the video certainly does help.

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      trazor 10 months ago

      Hey Dan, I started experiencing this issue a few days ago and I was always able to get the fan to start using the stick method. I ordered a new capacitor as my local hardware store didn't have one in stock, but now the issue is happening again and the stick method is no longer working. Took a video at https://drive.google.com/file/d/0B_brPQYA8oxlVWZvQ... if it helps. Thoughts?

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      Dan Robbins 10 months ago from Ohio

      Gee - DO NOT CONNECT until you know for sure. The "H" or Herm is to go to the compressor. The "F" or fan is to go to the fan and the "c" is your common. That said, you could perhaps google the model number of your unit and perhaps be lucky to find a wiring schematic. Not always but sometimes these are available on the net. Best of luck but do not guess. Thank you for reading.

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      Dan Robbins 10 months ago from Ohio

      Sheri - In my opinion, if I make a repair and it almost immediately needs the same repair again...there's an underlying problem and he should be looking at why it keeps blowing capacitors. Now if you're tripping breakers on top of it he should be aware that there's a short somewhere in the circuit and be looking to fix that before throwing more parts in the unit to be burnt or shorted out since the underlying issue sounds like it hasn't been fixed. Sorry you're having a hard way to go but it may be time to find a new repair guy or speak to a manager at whom you're dealing and have them waive any service call fees based on the fact that they aren't resolving the issue and need to send another tech to see why??? Thanks for reading.

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      Dan Robbins 10 months ago from Ohio

      Hilary - Thank you for reading. It does sound like a capacitor then and I'd make the repair. Starting the fan with a stick is just a test not a solution. Beyond that, if it ain't broke, don't fix it.

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      Hilary 10 months ago

      Hey, this buzzing noise but no fan thing happened to me yesterday. Just stumbled upon this article, so I turned the a.c. back on and walked outside to find a stick and test it. Alas, the fat was running on its own. Should I assume it still needs help? Possibly have a tune up? Or should I count my lucky stars? My house is on the market and I am moving put of state a week from today, and already have a tech schedule to come sometime today.

      Thanks

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      Sheri 10 months ago

      Good morning Dan,

      Do you know what would cause the A/C unit to trip the breaker? Recently, a tech replaced the capacitor (twice) after the unit was making a humming noise. Now, at least once a day the unit is tripping the breaker in the house. Flip the switch on the breaker and it starts working again. I could call the tech back out to the house, but it's expensive and I feel as though I'm getting the run around. Any ideas?

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      gee 10 months ago

      I have a 20 yo York AC. I took off the capacitor and forgot to mark the wires. I have one red (common), but two slightly different shade of brown wires, no white strip. Im not sure which is Herm and which is Fan. If I connect and they are crossed, will I damage anything if its wrong?

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      Dan Robbins 10 months ago from Ohio

      Tammi - I'm sorry but this is really to vague for me to offer any solid opinion. I wish I could help more but there would need to be more technical information for me to offer any useful opinion. Thanks for reading.

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      Dan Robbins 10 months ago from Ohio

      Elizabeth - I'm really not sure what exactly the issue is but if in fact the contactors keep burning up then it sounds as if there is a voltage issue coming from the panel perhaps or a short in the circuit somewhere. You would need some pretty decent electrical tools and knowledge to pinpoint the issue. Sorry if that doesn't help much but it can be difficult in certain scenarios to diagnose from afar. Thanks for reading.

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      Dan Robbins 10 months ago from Ohio

      Pierre, Very nice description of problem and things you've done as well as knowledge. Very helpful for me to help you. I would be thinking the contactor is suspect and like the capacitor is cheap and worth a try. The contactor may be moving freely but that doesn't mean the 24V coil inside of it is working. That's what pulls in the contact. With the power on and again, a stick (or something non-conductive)...you could push it in and see if it makes the unit work. If it does, then that's likely your problem. If not, it's likely time to call a tech. The problem with power surges or lightning strikes is that it can take out multiple components and thus sometimes you replace one thing only to find out another is also shot. Hopefully that's not the case here and that this will help. Thanks for reading and commenting. Many requests are so vague that I have no idea where to begin. That doesn't mean I can say for sure what your particular problem is from here but it certainly tells me where to look next. Best of luck!

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      Tammi 10 months ago

      So it stay cool in one bedroom an the rest stays hot have the temperature set to 70 it just keeps going up to like 80

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      Elizabeth 10 months ago

      Inside a/c was not blowing cold air. I checked the outside heating pump and the relay contactor seemed to be burnt. I of course replaced it but within the 2 week period it burned again. I used the relay contactor on my other heating pump unit but the heating pump will start then shut off. Can you please tell me what's causing the burning issue?

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      Pierre 10 months ago

      Hi Dan,

      Very helpful column, thanks. After a storm, (not sure if there was lightning) I came back to hear the AC making a loud humming noise, no fan, no condenser movement. Inside blower on. Outside unit getting hot. Unit fan would not pick up on its own and spin when coaxed. (it does spin freely, just stops after a few seconds). Thermostat ok. Suspect sounded like the capacitor, as per other descriptions. But top (and bottom) of capacitor not rounded, but flat. Took recommended precautions and changed capacitor with a replacement with the same specs. Unfortunately, same sound, no movement, fan does not pick up on its own when tweaked. Is there another likely suspect that my "layman's" skills could probably handle, such as changing out the contactor (though contact seems to move up/ down fine), or is it time to call in the HVAC pros? (my limited skills do not extend to intelligently testing circuits, though I could pull out and replace a contactor. Too much guessing? Any other suspect items I can test? (I do have a voltmeter with ohm readings).

      Thanks again for your opinion

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      Dan Robbins 10 months ago from Ohio

      Michelle - Seems the trouble would be with the indoor unit if there is no air blowing in the house. Unfortunately I'd need to know much more to help say what that could be. First you need to confirm there is power to the indoor unit and then figure out where the loss of power to the fan is. Unless you're electrically equipped and knowledgable, that could be difficult for you to do. Sorry. Wish I could help more. Thanks for reading.

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      Michelle 10 months ago

      I came home from work and my ac is not blowing In the house but the fan outside is on and spinning. What could it possibly be?

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      Dan Robbins 10 months ago from Ohio

      Edd - perhaps. The dual capacitor helps the fan and compressor so it's possible it's still the problem. Possible being the key word. Thank you for reading.

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      Dan Robbins 10 months ago from Ohio

      Well changing the fuses won't really help here because the fan wouldn't spin at all. The capacitor may be a dual cap and only the compressor side is bad potentially and would be why the fan is still running. Perhaps reread this article and see if it helps a second time around. If not, you'd best call a professional because though the service can be costly, so can guessing. Thanks for reading and commenting.

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      Dan Robbins 10 months ago from Ohio

      RV Stewart - Hmmmm. I'm not sure. I suppose a hard start COULD be helpful but not sure what this is at night. I'm sorry but I'm stumped here. Thanks for reading.

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      Dan Robbins 10 months ago from Ohio

      Tharpo - Though I'd prefer no one gets shocked, I'm glad you got it running and are here to tell. Haha. Thanks for the feedback!

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