Pressure/Temperature Relationship

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Fig 1: Identifying Pressure/Temperature Relationship

Courtesy of BMW OF NORTH AMERICA, INC.

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

Fig 2: Identifying Evaporator And Condenser Pressure Relationship

Courtesy of BMW OF NORTH AMERICA, INC.

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.