How Window AC Units Work

Air conditioners can differ from model to model. However, they all operate on similar principles. When you switch the air conditioner on, the thermostat control sends 120 volts of alternating current to the compressor and the fan motor. The compressor acts as a pump and compresses refrigerant (in gas form) into the condenser coils located near the back of the Window AC unit. This is also where the gas is condensed into a hot liquid.

The condenser coils then dissipates the heat as the liquid travels through them. Once the refrigerant has escaped through the capillary tubes and condenser coils, it travels to the evaporator coils located near the front of the unit. As the refrigerant liquid enters these coils, it expands into a gas, which makes the coils cold. The gas is then actively flowing through the coils to a suction line attached to the compressor. With the help of the compressor, the gas is then converted back into a liquid and the cooling cycle continues. At the same time, the blower wheel is rotated by a fan motor, which brings in air to be cooled by the evaporator coils before recirculating it back into the room. The same motor also operates the condenser fan blade, which blows outside air through the condenser coils to cool them.


The air temperature is regulated by the thermostat control. Depending on the model, the control may be a thermostat switch and sensing bulb assembly or an electronic control board that works with the sensor. The sensing bulb or electronic sensor is clipped to the front of the evaporator coils to monitor the temperature of the air entering the coils. Once the room has sufficiently cooled, the thermostat control shuts off the voltage to the compressor. Some models, which use a vent, can operate the fan motor only to draw in cool air at night. However, the vent must be closed when the appliances are actively cooling the air for the system to work properly


Be aware that it’s normal for water to collect in the bottom of the air conditioner. A slinger ring on the condenser fan blade picks up this water and sprays it onto the condenser coils. This helps the coils dissipate heat. To prevent the water from dripping into the room, the AC unit should be tilted back slightly when installed. If you can hear the unit running, but the air does not appear to be recirculating, the fan motor has most likely burned out and will need to be replaced. If the air does not cool at all, the compressor may have failed or the refrigerant may have leaked out of the system. Be aware that a licensed technician must perform any repairs to the refrigerant system.

If you have any further questions please contact Innovair at 305-463-9998