Pressure/Temperature Relationship

Raising the pressure of a vapor raises its temperature; lowering the pressure decreases its temperature.







In an air conditioning system, a compressor is used to increase the pressure of the refrigerant; this raises its temperature. The refrigerant vapor entering the condenser is hot.

In BMW air conditioning systems, an expansion valve is used to lower the pressure of the refrigerant; the refrigerant in the evaporator is cold.

Automotive A/C Systems are designed to operate at pressures that keep the refrigerant at the optimum temperature for taking heat out of the passenger compartment.