Window Air Conditioner

Window air conditioner is sometimes referred to as room air conditioner as well. It is the simplest form of an air conditioning system and is mounted on windows or walls. It is a single unit that is assembled in a casing where all the components are located.

This refrigeration unit has a double shaft fan motor with fans mounted on both sides of the motor. One at the evaporator side and the other at the condenser side.

The evaporator side is located facing the room for cooling of the space and the condenser side outdoor for heat rejection. There is an insulated partition separating this two sides within the same casing.

Front Panel

The front panel is the one that is seen by the user from inside the room where it is installed and has a user interfaced control be it electronically or mechanically. Older unit usually are of mechanical control type with rotary knobs to control the temperature and fan speed of the air conditioner.

The newer units come with electronic control system where the functions are controlled using remote control and touch panel with digital display.

The front panel has adjustable horizontal and vertical(some models) louvers where the direction of air flow are adjustable to suit the comfort of the users.

The fresh intake of air called VENT (ventilation) is provided at the panel in the event that user would like to have a certain amount of fresh air from the outside.

The mechanical type is usually lower in price compared to the electronic type. If you just want to cool the room and are not too particular about aesthetic or additional functions, the mechanical type will do the work.

Indoor Side Components

The indoor parts of a window air conditioner include:

  • Cooling Coil with a air filter mounted on it. The cooling coil is where the heat exchange happen between the refrigerant in the system and the air in the room.
  • Fan Blower is a centrifugal evaporator blower to discharge the cool air to the room.
  • Capillary Tube is used as an expansion device. It can be noisy during operation if installed too near the evaporator.
  • Operation Panel is used to control the temperature and speed of the blower fan. A thermostat is used to sense the return air temperature and another one to monitor the temperature of the coil. Type of control can be mechanical or electronic type.
  • Filter Drier is used to remove the moisture from the refrigerant.
  • Drain Pan is used to contain the water that condensate from the cooling coil and is discharged out to the outdoor by gravity.

Window Air ConditionerA typical window unit.

Outdoor Side Components

The outdoor side parts include:

  • Compressor is used to compress the refrigerant.
  • Condenser Coil is used to reject heat from the refrigeration to the outside air.
  • Propeller Fan is used in air-cooled condenser to help move the air molecules over the surface of the condensing coil.
  • Fan Motor is located here. It has a double shaft where the indoor blower and outdoor propeller fan are connected together.


During operation, a thermostat is mounted on the return air of the unit. This temperature is used to control the on or off of the compressor. Once the room temperature has been achieved, the compressor cuts off.

Usually, it has to be off for at least 3 minutes before turning on again to prevent it from being damaged. For mechanical control type, there is usually a caution to turn on the unit after the unit has turned off for at least 3 minutes. For electronic control, there is usually a timer to automatically control the cut-in and cut-out of compressor.

The evaporator blower fan will suck the air from the room to be conditioned through the air filter and the cooling coil. Air that has been conditioned is then discharge to deliver the cool and dehumidified air back to the room. This air mixes with the room air to bring down the temperature and humidity level of the room.

The introduction of fresh air from outside the room is done through the damper which is then mixed with the return air from the room before passing it over the air filter and the cooling coil.

The air filter which is mounted in front of the evaporator acts as a filter to keep the cooling coil clean to obtain good heat-transfer from the coil. Hence, regular washing and cleaning of the air filter is a good practice to ensure efficient operation of the air conditioner.

Heat Pump Window Air Conditioner

In temperate countries, heating of the room is required. A heat pump window air conditioner unit is able to cool the room during summer and heat the room during winter. A reversing valve (also known as 4-Way-Valve) is used to accomplish this.

During heating operation, it reverses the flow of the refrigerant which results in the evaporator to act as a condenser and the condenser as evaporator.

Frigidaire Window Air Conditioner

If you have a Frigidaire window air conditioner with cooling capacity of 15,000-28,500 Btu or you want a better understanding of how this type of air conditioner is installed, read the installation instruction here.

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