The Refrigerant Cycle
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.
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 receiver drier element. The receiver drier element is designed to remove moisture from the refrigerant.
The outlet of the receiver drier element is connected to the Thermostatic Expansion Valve (TXV). The Thermostatic Expansion Valve (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 and sends a signal to the PCM. If the temperature of the evaporator 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.
| Item | Description |
|---|---|
| 1 | A/C evaporator |
| 2 | A/C evaporator outlet temperature sensor |
| 3 | Thermostatic Expansion Valve (TXV) |
| 4 | A/C charge valve port (low side) |
| 5 | A/C suction line |
| 6 | A/C compressor |
| 7 | A/C pressure relief valve |
| 8 | A/C pressure transducer |
| 9 | Low-pressure vapor |
| 10 | High-pressure vapor |
| 11 | Low-pressure liquid |
| 12 | High-pressure liquid |
| 13 | Compressor discharge line |
| 14 | Receiver Drier Element |
| 15 | A/C condenser |
| 16 | Condenser-to-evaporator line |
| 17 | A/C charge valve port (high side) |