Refrigerant Cycle

THE REFRIGERANT CYCLE

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

The A/C condenser core, 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 core and enters the inlet side of the receiver/drier.

The receiver/drier is designed to remove moisture from the refrigerant. The refrigerant, still at high pressure, exits the receiver/drier and enters the thermostatic expansion valve.

The thermostatic expansion valve is the restriction in the refrigerant system that creates the high-pressure buildup in the A/C condenser core and separates the high and low-pressure sides of the A/C system. As the liquid refrigerant leaves 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 core, it absorbs heat from the passenger compartment airflow passing over the plate/fin sections of the A/C evaporator core. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler passenger compartment air can no longer support the same humidity level of the warmer air and this 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 compressor again increasing the pressure and temperature of the refrigerant.

The A/C thermostatic cycling switch interrupts compressor operation before the external temperature of the A/C evaporator core gets low enough to cause the condensed water vapor (excess humidity) to turn to ice. It does this by supplying an ON/OFF command to the PCM.

The low charge protection switch protects the A/C compressor in the event of a low refrigerant charge. The switch interrupts the signal between the PCM and ground, when the low side refrigerant pressure drops below acceptable levels.

The refrigerant containment switch protects the A/C compressor if system pressure becomes too high. The switch interrupts the signal between the PCM and low charge protection switch.

The A/C compressor relief valve will open and vent refrigerant to relieve unusually high system pressure.