Air Conditioner Pump. As condensation drips from the coils of your air conditioner, it collects in a drip pan. Then, the air conditioner pump pushes the moisture outside or into some kind of drainage system. If your condensate line cannot be repaired, you'll need an AC pump to remove the excess water. The compressor pumps, or forces, the liquid from the evaporator into a condenser and expansion valve, and then back to the evaporator. The engine drives the compressor with a belt. In action, the compressor takes the low pressure refrigerant from the evaporator and compresses it according to speed and air temperature.