All door closers exert force against opening. If the force needed to open the door is excessive, and the spring tension of the door closer is adjustable, the level of force exerted by the spring can be reduced. Some door closers have preset spring tension. These have sizes according to the strength of their spring. For example, on an exterior door that is three feet wide, one would usually use a size four door closer. If one used that same closer on a door that is thirty inches wide, one might find that opening the door has become difficult.
Another reason the door closer might make the door hard to open is that it is installed incorrectly. For example, if the arm were attached to the spindle in the wrong position, or if the closer was installed in the wrong location, it might make the door hard to open.