Testing A Car A/C Compressor Using A Multimeter


The compressor in your car air conditioning unit circulates refrigerant through your A/C unit to create cool air. The serious symptoms of a faulty A/C compressor include the A/C cycling on and off repeatedly while operating, or your engine making a high-pitched grinding sound like metal scratching against metal.

This is caused by a worn-out bearing in the A/C compressor or a seized drive belt. You should test your compressor if you notice any of these signs. Below is a guide to help you test your car A/C compressor using a multimeter.

Step 1: Turn Off the Vehicle

Your vehicle should be turned off. Make sure your car’s moving parts are stationary under the hood by shutting off the engine. Wait until your engine or internal parts have cooled down before checking your compressor.

Step 2: Locate the Clutch

Locate your A/C compressor clutch under the hood of your car. You can usually find your compressor clutch under the hood near the front of your car on the left side. The component will look like a cylindrical piece of metal with tubes and wires going through it.

Step 3: Look for Damages

The compressor should be examined for damage. Older vehicles are likely to have a rusted compressor. The compressor should be checked for rust or holes. Ensure that the tubing and wires aren’t damaged, frayed, or disconnected. Replacing them is more affordable than buying a whole new compressor if they’re broken.

Step 4: Disconnect Battery Wires

Your battery wires should be disconnected from the A/C compressor. Compressors should have wires running from their tops or sides. The white wire is the live wire, and it carries electric current, while the black wire is the ground wire that carries ground current.

You can remove the plastic fittings and wires by pressing on their sides and pulling them. If you do this correctly, you should be able to see the contacts that you will use to test the compressor.

Step 5: Insert Multimeter Pins

The pins of the multimeter should be inserted into the plastic fittings in order to get a reading. Connect the pins of your multimeter to the contacts and adjust your multimeter to continuity. By setting your multimeter to continuity, you can check whether current is properly flowing through your compressor clutch.

Step 6: Examine the Readings

If the reading falls below 3 ohms or rises above 5 ohms, replace the coil. If the multimeter reads 0 ohms, this indicates that your wires are bad and need to be replaced. In most cases, a reading over 5 ohms indicates that you have a faulty coil, and your diodes need to be checked by a mechanic.

Step 7: Connect A/C Compressor Clutch

Try connecting your A/C compressor clutch to a 12-volt battery to see if it engages. Your black battery cable or the negative cable should be connected to the grounded contact on the compressor. Connect the black wire to the negative side of the battery.

The positive, or red wire, should be connected to the positive side of the battery. Make contact with the live compressor clutch wire with the metal end of the wire. In this way, you should be able to engage and disengage the clutch. There could be a problem with the clutch contacts or the clutch itself if the clutch does not move or makes a noise.

It is crucial to follow all the safety measures while testing an A/C compressor in order to prevent risks. You can always seek professional help to get your compressor tested.