AC Principles and Components

The refrigeration cycle and the components that move heat out of the cabin.

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What you will learn

Describe the refrigeration cycle
Name the main components
Explain high and low sides

Air conditioning does not create cold — it moves heat. Refrigerant leaves the expansion device as a cold, low-pressure mist, absorbs cabin heat in the evaporator, and is then compressed so it can release that heat to the outside air in the condenser. The cycle repeats continuously while the compressor turns.

The low side runs from the expansion device through the evaporator back to the compressor; the high side runs from the compressor through the condenser to the expansion device. Knowing which side you are measuring is the basis of AC diagnosis.

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Component	Job
Compressor	Compresses refrigerant, creating the pressure difference
Condenser	Releases heat to the outside air
Expansion valve / orifice	Drops pressure and temperature
Evaporator	Absorbs heat from the cabin air
Receiver/dryer	Stores liquid and removes moisture

Real-world example: a car that cools well on the motorway but blows warm in traffic usually has a condenser airflow problem (fan or fins), because the cycle depends on releasing heat outside.

Key points

AC moves heat; it does not create cold.
Compressor creates the pressure difference; expansion drops it.
Know which side (high/low) you are testing.

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Key points

Refrigerant absorbs heat in the evaporator and releases it in the condenser
The compressor creates the pressure difference
The expansion device drops pressure and temperature

All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.