Auto A/C Terms - Glossary
Head Pressure

Head pressures represent the pressure of the refrigerant in the A/C system on the high pressure side of the system. Head pressures are also referred to as high side pressures or just the high pressure.

When it comes to pressures of refrigerant, every A/C system is divided into two sides. The high side of the A/C system starts at the compressor discharge. Technically, right at the discharge reed valve internally in the compressor. The high pressure side also includes the A/C condenser and liquid line between the condenser and expansion valve or orifice tube. At the expansion valve, the refrigerant pressures are reduced and changed into low pressure, ending the high pressure side of the A/C system.

Typical head pressures or high pressure gauge readings on an average auto A/C system will range between 2 and 2 and one half times the ambient air temperature when expressed in degrees F. As an example, on a typical summer day that is 80 degrees F, the expected high pressure range on a properly operating A/C system would be between 160 and 200 psi. 160 represents 2 times the ambient air temperature while 200 psi represents about 2 and one half times the ambient air temperature.