The Refrigerant Cycle

WARNING: This page is about a different car, the 2013 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

During A/C system shutdown, the refrigerant pressures are equal throughout the system. When the A/C compressor is in operation, it uses a piston pump to compress the cool vapor, causing it to become high-temperature/high-pressure vapor. The high-temperature/high-pressure 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. The receiver/drier is designed to remove moisture from the refrigerant.

The outlet of the receiver/drier is connected to the TXV. The TXV provides the orifice, which is the restriction in the refrigerant system, and separates 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 tube and 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 this excess moisture condenses on the exterior of the evaporator tubes 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 PCM controls the A/C clutch relay. The evaporator temperature sensor monitors the temperature of the air that has passed through the evaporator core and sends a signal to the PCM. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze, the A/C clutch is disengaged by the PCM.

The line pressure is monitored so that A/C compressor operation is interrupted if the system pressure becomes too high or too low.

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