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How to Replace an Air-Conditioning System's Condensate Pump

Bert spent 25 years working as a home-improvement and residential construction contractor in central Florida.

The condensate pump on an air-conditioning system usually runs for many years without any major issues.

Unfortunately, when the pump fails, it often happens unexpectedly and at the worst time, such as after work on a hot summer day when a professional service technician charges "emergency" or "after-hours" rates.

An experienced technician starts the service call investigating the most common problem areas, which includes the condensate-drain system. If the condensate pump failed, the air-conditioning system would continue to dump condensate into the holding tank until the water level activates the pump's safety switch.

A view of the condensate pump on an air conditioning unit.

A view of the condensate pump on an air conditioning unit.

Troubleshoot the Existing Condensate Pump

Before spending unnecessary money on a new condensate pump, troubleshoot the old pump. Sometimes it only takes a simple fix to restore the pump to working order. Slowly pour water into the holding tank until it activates the pump-motor's float switch or the holding tank overflows.

  1. Check the electrical circuitry: If the pump motor failed to turn on, inspect the fuse. The fuse protects low-voltage circuitry from catastrophic failure. If the fuse shorted, inspect the wiring for damaged insulation or an exposed conductor, and fix as necessary with electrical tape. Replace a blown fuse with an exact match; never increase the fuse's amperage rating. If the fuse checks out but the pump still fails to energize, check the high-voltage connection for proper voltage.
  2. Inspect the pump motor's actuator: If the pump motor failed to turn on or remained energized after it removed all condensate from the holding tank, you can suspect water-deposit buildup on the pump's actuator. Occasionally cleaning water deposits from a stuck actuator temporarily fixes the pump. However, the buildup on the actuator usually interferes with its actuator within a short amount of time. Open the pump's holding tank and remove sludge and water deposits.
  3. Examine the discharge tubing: If the pump motor energized but did not evacuate the holding tank, suspect a clogged drain line. This often happens after the air-conditioning system remained off for an extended period of time. Sludge forms in the stagnate water contained inside the holding tank. When the pump motor turns on, it pulls the sludge out of the tank and forces it into the discharge tubing. Occasionally large pieces of sludge create a dam in a sharp bend or where two pieces of tubing meet. To remedy a clogged condensate drain, simply disconnect the drain line from the pump's discharge port and blow compressed air through the tubing. Placing a condensate drain cleaning tab in the pump housing during the system's yearly preventive maintenance checkup inhibits sludge buildup, which lessens the likelihood of this problem occurring in the future.

Disconnect the Electricity

  1. Turn off the circuit breaker with the "Furnace" or "Air Handler” label: This disconnects the electricity, preventing accidental electrical shorts and keeps the technician safe. Keep it off for the entire procedure.
  2. Disconnect the old condensate pump from its high-voltage electrical source: Many systems plug into a standard 120-volt GFCI-protected wall receptacle located on or near the furnace. If so, simply pull the plug from the receptacle. Occasionally, the pump motor hardwires directly into the furnace's high-voltage terminal block. If so, take note of the wire connections for future reference, then disconnect the wiring.
  3. Disconnect the condensate pump's low-voltage circuitry: The condensate pump's high-water safety switch connects in series with the furnace's thermostat circuitry. The connection method depends on the model. Follow the thin-gauge two-strand wire set exiting the furnace toward the condensate pump. Some models use exposed wire nuts, while others need the condensate pump's electrical compartment opened to access the connections.
Many systems use 3/4-inch PVC pipe as a furnace or air-conditioning drain.

Many systems use 3/4-inch PVC pipe as a furnace or air-conditioning drain.

Remove the Old Condensate Pump

  1. Remove the discharge tubing: Loosen the clamp securing the discharge tube to the pump's barbed discharge fitting, using the appropriate tool. Some pumps use hose clamps requiring a slotted screwdriver, while others use a pinch clamp that squeezes together with pliers. Grip the pump housing with one hand and the discharge tubing with the other. Twist the tubing back and forth while pulling it off the fitting.
  2. Disconnect the air-conditioning and furnace drains: If the condensate pump sits on a movable support, slide the support away and lower the pump. The drain pipes from the air conditioner or furnace will slide out of their respective pump-housing intake ports. If the pump sits on the floor or some other unmovable surface, cut the drain pipes about six inches up from the pump housing. Lift the furnace drain pipe out of the condensate pump's intake port. Save the short pieces of pipe for reinstallation.
  3. Remove the old furnace condensate pump: Disconnect any mounting brackets using the appropriate screwdriver. Discard the old unit.

Prepare the Discharge Tubing

  1. Inspect the discharge tubing: Visually inspect the vinyl discharge tubing connected to the pump motor; look for worn areas. Pay particular attention to the areas where the tubing touches other objects, such as mounting clamps and the furnace itself. Replace damaged tubing as needed.
  2. Flush the discharge tube: Clean the discharge tubing with compressed air, using an air compressor, air tank, or as a last resort, a bicycle pump. Attach the compressed-air tool to the drain tube and apply air, removing all water and sludge. Continue to push air through the discharge tubing until the air flows freely. This removes all sludge buildup.
  3. Replace damaged tubing: If vibration created excessive wear or an unmovable blockage prevented airflow, replace the tubing. Unfortunately, this often requires fishing 1/4-inch inside-diameter tubing through an attic or crawl space towards a suitable discharge area outside or to a nearby gravity-fed drain. When running the drain toward the outside, create a water trap in the tubing. Some technicians make a loop in the tubing near the pump as a water trap, others form a large U-shape bend. Obviously, a skilled technician avoids terminating a drain line above a doorway or window, and avoids spillage onto a walkway. When connecting to an existing drainage system, such as a sink or washing machine drain, the condensate must enter the drain system upstream of the trap. When connecting to a sink drain, replace the sink drain's standard tailpiece with one equipped with a side port. Slip the end of the condensate pump's discharge tubing into the side port.
DIY installation of a new condensate pump, if necessary, can save you money.

DIY installation of a new condensate pump, if necessary, can save you money.

Install the New Condensate Pump

  1. Prepare the new condensate pump: If the old condensate pump sat directly on the floor, consider lifting the pump off the ground with a brick or other support. The raised position makes future preventive-maintenance servicing easier. With a raised platform, a technician simply slides the support out from under the pump, then lowers the pump without needing to cut the PVC drain pipes from the furnace or air-conditioning coil.
  2. Connect the air-conditioning and furnace drains to the condensate pump: If the pump housing sits on a raised platform, position the end of the air-conditioning and furnace drain pipes inside their respective intake ports on the pump housing, set the pump in place and replace the platform support. If the technician cut the drain pipe while removing the old pump, position the drain opening in the pump housing directly below the existing drain pipe. Slip the small cut piece into the intake port and splice the two pieces together with a coupling. Repeat this for the furnace drain, when applicable.
  3. Attach the discharge tubing: Force the end of the discharge tube onto the condensate pump's barbed discharge fitting. The end of the discharge tube must completely cover all of the discharge fitting's barbs. Position the clamp on the discharge tubing about 1/8 inch from the end of the discharge tube. The clamp locks the discharge tube against the pump housing's discharge fitting.
Wire nuts protect electrical connections from accidental shorts.

Wire nuts protect electrical connections from accidental shorts.

Make the Electrical Connections

  1. Attach the low-voltage circuit: Connect the condensate pump's safety switch to the furnace's low-voltage wire set. The open-or-closed nature of this switch makes these wire connections interchangeable. If the pump model uses exposed wire leads, simply twist one of the condensate pump's safety switch wire strands around one of the furnace's low-voltage wire strands. Protect the connection with a wire nut. Repeat this with the second wire group. If the unit uses a contained electrical compartment, open the compartment with the appropriate screwdriver. Fish the furnace's low-voltage wire into the compartment through the wire-access hole, make the electrical connections, then close the compartment.
  2. Make the condensate pump's high-voltage connection: Many units come from the manufacturer with a 3-prong 120-volt plug attached to the end of the high-voltage cord. Either push this plug into a wall receptacle or cut the plug off and hard wire the pump motor's wire set into the furnace's terminal block, using the notes taken during disassembly as a guide. Flip the furnace's circuit breaker to the "On" position.

Test the New Condensate Pump

Pour water into the pump's holding tank. Eventually the rising water should lift the float switch and turn on the pump motor. A properly working condensate pump removes a significant amount of water from the holding tank before cycling off. This process takes less than 30 seconds. If the motor fails to turn on, check each electrical connection for solid contact and proper voltage.

Placing a condensate drain cleaner tablet in the pump's holding tank prevents sludge buildup. I have used SimpleAir Drain Line tablets in my air conditioning system. I place a couple of tablets in the air conditioner's drip pan every spring. Throughout the year, they slowly dissolve, limiting algae buildup in the drain line.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2018 Bert Holopaw