Air Conditioning (A/C) System

The air conditioning system is a self-contained system, completely sealed off from the atmosphere. While operating, it recycles refrigerant through the system.

The major components of the A/C system include:

• The compressor
• The condenser
• The receiver/dryer
• The expansion valve
• The evaporator

When the A/C compressor clutch is engaged, the compressor draws in low-pressure refrigerant gas. It compresses the gas and moves it to the condenser. Compressing the gas raises its temperature above that of the outside air. As the hot, high-pressure gas flows into the condenser, cooler air flowing across the condenser absorbs heat from the gas. As the refrigerant gives up heat to the air, it condenses and changes to a liquid.

The high-pressure liquid refrigerant flows from the condenser to the receiver/dryer. The dryer contains a filter screen, to remove small impurities, and a drying agent to absorb and hold any moisture. The dryer is also a storage tank; a steady supply of liquid refrigerant is drawn out of the bottom of it, to the expansion valve. The expansion valve meters the refrigerant, so that its pressure drops, causing it to boil as it enters the evaporator.

Hot air is blown across the evaporator as the refrigerant boils. Heat from the air is transferred to the refrigerant, causing the air to be cooled. The hot, low-pressure refrigerant is then drawn back into the compressor to complete the loop.

In addition to cooling the air, the A/C system also dehumidifies it.

Additional components of the A/C system include:

• The compressor clutch
• The pressure switches
• The evaporator temperature sensor

  The compressor clutch allows the compressor to be disengaged when the A/C system is not used. The pressure switches cause the compressor clutch to disengage when the pressure in the system is too low or high, to prevent damage. The evaporator temperature sensor also causes the compressor clutch to disengage when the evaporator temperature drops close to freezing. This prevents ice or frost from forming on the evaporator fins.

Fig 1: Identifying Air Conditioning (A/C) System Flow Diagram

Courtesy of BMW OF NORTH AMERICA, INC.