Testing an Air Compressor Pressure Switch

a hand adjusting an AC vent in a car
What You'll Need
Ohm meter
Compressed air

The air conditioner on your vehicle has an air compressor pressure switch, to regulate the pressure of the refrigerant. When this air compressor pressure switch is not working correctly, the air conditioner will either not work at all, or not create enough cold air. If you are having problems with your air conditioner, here are some steps to take in testing the air compressor pressure switch.

Step 1 - Disconnect Battery

Disconnect the battery terminals before working on the air conditioner.

Step 2 - Remove Cover for Compressor Unit

There should only be one or two screws holding the cover on the unit. Remove these with a slotted screwdriver.

Step 3 - Disconnect Terminal Wires

Locate the wires to the switch and disconnect them. They will either be a blue or brown color.

Step 4 - Test Switch with Air

Once you have access to the pressure switch, blow some air on it from an air compressor or compressed air can.

Step 5 - Connect Ohm Meter

With the air applied to the switch, connect the leads of the Ohm meter to each of the wires. If the pressure switch closes when the air is applied, the meter will read zero. If not, the meter will read 'OL' which means open circuit.

Step 6 - Make Adjustments

If you find that the pressure switch is not working correctly, adjust the set screw or replace it.