The system contains a refrigerant. The refrigerant is either a gas or a liquid, depending on the temperature and the pressure. The refrigerant is a heat exchange medium.

Heat is required to change the liquid refrigerant (134a) into a gas.

When the R-134a refrigerant changes from a liquid to a gas in the evaporator (3) , the vehicle cab cools.

The air that passes through the evaporator transfers heat to the R-134a refrigerant. The R-134a refrigerant absorbs the heat and changes into a gas. The blower motor circulates the air in the cab.

The following steps occur in the refrigerant cycle:

1. The refrigerant cycle starts at the compressor (10).

The refrigerant is a low pressure, low temperature gas when it enters the compressor.

2. The refrigerant is compressed to a high pressure, high temperature gas.
3. The gas flows through the condenser tube.
4. The gas transfers heat to the cooler air that is passing through the condenser cooling fins (8).
5. The high pressure, high temperature gas changes into a high pressure, high temperature liquid.
6. The high pressure liquid passes through the receiver/dryer or dehydrator.

The following actions occur in the receiver/dehydrator (7):

6.1.	A screen filters the refrigerant.

6.2.	A desiccant removes moisture from the refrigerant.

6.3.	The receiver/dryer or dehydrator also stores the refrigerant.

7. The liquid refrigerant flows through the expansion valve (5).
8. The refrigerant changes to a low pressure, low temperature liquid in the evaporator (2).
9. Warm inside air flows through the cooler evaporator core or fins (3).

The warm air transfers heat to the low pressure, low temperature liquid in the evaporator and the low pressure liquid becomes a low pressure gas.

10. The low pressure vapor returns to the compressor.
11. The cycle begins again.