The Refrigerant Cycle

Courtesy of FORD MOTOR CO.

During stabilized conditions (A/C  system shutdown), the refrigerant pressures are equal throughout the system. When the A/C  electric compressor is in operation, it increases refrigerant vapor pressure, raising its temperature. The high-pressure and high-temperature vapor is then released into the top of the A/C  condenser core.

The A/C  condenser, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C  condenser and enters the inlet side of the A/C  receiver/drier (integral to the condenser). The receiver/drier is designed to remove moisture and contaminants from the refrigerant system.

The outlet of the receiver/drier is connected to the Thermostatic Expansion Valve (TXV). The TXV provides the orifice, restricting refrigerant flow and separating the high and low pressure sides of the A/C  system. As the liquid refrigerant passes across this restriction, its pressure and boiling point are reduced.

The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C  evaporator, it absorbs heat from the airflow passing over the plate/fin sections of the A/C  evaporator. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler air can no longer support the same humidity level of the warmer air and the excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.

The refrigerant cycle is now repeated with the A/C  electric compressor again increasing the pressure and temperature of the refrigerant.

The PCM  monitors the evaporator temperature sensor thermistor as air is passed through the evaporator core and controls the A/C  electric compressor speed. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze, the A/C  electric compressor reduces it speed.

The high-side line pressure is monitored so that A/C  electric compressor operation is interrupted if the system pressure becomes too high or too low (low charge condition).

The A/C  electric compressor has internal thermal protection in the ACCM  to interrupt compressor operation if the compressor exceeds temperature limits

The A/C  electric compressor pressure relief valve opens and vents refrigerant to relieve unusually high system pressure.