AC Compressor

The compressor, condenser and evaporator work together, but each has a different job. During a typical cabin-cooling cycle, refrigerant circulates through the AC system and carries heat away from air passing over the evaporator. The refrigerant and the air you feel at the vents follow separate paths.

The Three Parts at a Glance

What Does the AC Compressor Do?

Refrigerant vapour returning from the evaporator enters the compressor. Compression raises its pressure and temperature before the compressor sends it towards the condenser. This keeps the refrigerant moving through the cycle. The air you feel at the vents is cooled as it passes over the evaporator, rather than inside the compressor.

What Does the AC Condenser Do?

Hot refrigerant arriving at the condenser releases heat to the surroundings. In normal cooling operation, it condenses from vapour to liquid as it does so. The condenser helps heat leave the AC system; the air flowing through the vents is cooled at the evaporator instead.

What Does the AC Evaporator Do?

A blower moves air across the evaporator. Depending on the ventilation setting, the air may be drawn from outside or recirculated from the cabin. Refrigerant flowing inside the evaporator absorbs heat from that air and normally changes from a liquid mist to vapour. The air becomes cooler before it reaches the vents. During normal operation, air and refrigerant remain on separate paths: refrigerant is not blown into the cabin.

For possible signs of a refrigerant leak and how a workshop confirms the source, read our guide to signs of a leaking car AC evaporator.

How Do They Work Together?

In a typical cooling cycle, refrigerant absorbs heat at the evaporator, returns to the compressor as vapour and releases heat at the condenser. On its way back to the evaporator, it passes through a metering device, where its pressure drops. Depending on the system, that device may be an expansion valve or a fixed orifice tube. The refrigerant enters the evaporator on the low-pressure side of the circuit.

That is the basic route taken by the refrigerant, not a complete parts diagram for every vehicle. Fans, connecting lines and other components also play a part, and system layouts vary. The three parts cannot do one another's jobs: moving and compressing refrigerant is different from releasing heat or taking it from air passing over the evaporator.

Knowing those roles can help you follow a workshop's explanation. Warm air from the vents, for example, does not tell you which component, if any, needs replacing. If you want to explore signs of a blocked car AC condenser or why a new AC compressor might fail after replacement, our separate guides cover those questions.