The system contains a gas/liquid refrigerant, depending upon the temperature and the pressure, as a heat exchange medium.

Air passing through the A/C evaporator gives up heat to the R-134a liquid refrigerant. The R-134a requires heat in order to change to a gas or a vapor. The cooling of the air occurs when the R-134a changes from a liquid to a gas in the air conditioning (A/C) evaporator. The blower motor circulates the cool air in the cab.

The refrigerant cycle starts at the A/C compressor where the refrigerant enters as a low pressure (2), low temperature vapor. The refrigerant compresses to a high pressure (1), high temperature vapor. The high pressure, high temperature vapor gives up heat to the cooler air passing through the A/C condenser cooling fins as the vapor flows through the A/C condenser tubes. The refrigerant changes to a high pressure liquid when the refrigerant vapor gives up the heat. The high pressure liquid passes through the A/C receiver/dryer or the dehydrator. The refrigerant filters through a screen. The refrigerant uses a desiccant in order to dry the moisture. The A/C receiver/dryer or the dehydrator also acts as a storage tank for the refrigerant.

The liquid refrigerant flows through the A/C expansion valve. The liquid refrigerant changes to a low pressure, low temperature liquid in the A/C evaporator. Warm inside air flows through the cooler A/C evaporator core or fins. The warm inside air gives up heat to the low pressure, low temperature liquid in the A/C evaporator. The low pressure vapor returns to the A/C compressor and the cycle begins again.