If you think you have a problem with your A/C system but aren’t sure which component is causing the malfunction, it’s a good idea to connect your compressor to a pressure gauge.

A properly functioning A/C system should have 150 psi on the high side and 30 psi on the low side.

Obviously, the main problem people face when they have a broken air conditioning system is that the air coming out of the vents is not cool enough. Here is a list of pressure readings that characterize an A/C compressor that is not blowing cold air into your car‘s cabin:

250 psi / 30 psi = There is air somewhere in your system.

250 PSI / 50 PSI = The system is overloaded and the condenser does not cool. The condenser may be blocked.

225 PSI / 80 PSI = The expansion valve is likely to open too wide (not so if your A/C system has an orifice tube) Also, there may be too much refrigerant in your system.

200 PSI / 70 PSI = There is a blockage somewhere in your system, in the first or expansion device.

160 psi / 10 psi = The evaporator may freeze, the low pressure line may be faulty, or the expansion valve may be clogged. Check the evaporator, piping and expansion valve to locate the source of the problem.

150 PSI /> 10 PSI = Your expansion valve may be stuck open or there may be a leak somewhere in your system.

125 PSI / 30 PSI = The system is not charged enough or there is too much oil in the compressor.

100 PSI / 100 PSI = Compressor will not start because it is not receiving power or has a blown coil

50 PSI / 50 PSI = Clutch not engaged.

For more information on how to interpret AC pressure readings, see our instructions page on the subject.