How to Replace a Car's Air Conditioner Compressor Pressure Switch

What You'll Need
Air Conditioning Gauge Set
Air Conditioning Recovery Machine
Vacuum Pump
New Pressure Switch

Your car’s air Conditioner compressor pressure switch, is responsible for giving and cutting off power to the air compressor of the air conditioning system. When the pressure goes below 25 psi, the pressure switch cuts the power going to the compressor, making it shut off momentarily. This is important, in order to prevent the system from freezing up, due to extreme cold. When your air compressor pressure switch is faulty, the symptoms are usually freezing up of the air conditioning system, due to the compressor not turning off. The pressure switch then needs to be replaced.

Step 1: Remove the Refrigerant

Replacing the air conditioner compressor pressure switch, requires that you remove the refrigerant in the system first. Take note that it is not recommended to release the refrigerant into the air, since it contributes to greenhouse gases. Attach the recovery machine's hoses to the car’s air conditioning ports. There is a low-pressure port and a high-pressure port. To find the low-pressure port, follow the larger hose coming from the compressor, to the accumulator near the firewall. To find the high-pressure port, follow the smaller hose from the back of the compressor. It is found between the condenser and the radiator. Turn on the machine, until it removes all of the refrigerant. There is a gauge that will tell you how much refrigerant there is left.

Step 2: Replace the Pressure Switch

The air conditioner compressor pressure switch location on each type varies, so consult the manual of your car, to determine its exact position. Once you have determined where it is located, remove it by unscrewing it from its position. You also need to remove the rubber O-ring where it is attached, and replace it with a new one, that usually comes with the new pressure switch. Also, make sure that the pressure switch is up to spec, and is made exactly for your car.

Step 3: Remove Moisture

You need to completely remove moisture from the air conditioning system, before you test it and fill it up again with refrigerant. Get the air conditioning gauge set, and attach it to the pressure ports in Step 1. Now, attach the vacuum pump from the gauge set and turn it on, along with the service valves of the gauge set. This will remove all of the moisture in the system. Let it run for about 1 hour.

Step 4: Re-apply Refrigerant

Once the moisture has been removed from the system, close the service valves of the gauge set, and remove the vacuum pump attached to it. Install the can tap, that comes with the gauge set, and connect a can of refrigerant to it. Open the can and open the service valve on the gauge set, to refill the system with refrigerant. Keep on adding refrigerant and replacing the can, until the system is full. Refer to your car’s manual on how much refrigerant must go into the system.

Step 5: Testing

Remove all hoses and close all valves. Kill the engine and let it rest a bit. After 10 minutes or so, start the car and turn the air conditioning on full blast. Check to see if the air conditioner compressor pressure switch works.