How to Test a Compressor Clutch Coil: A Step-by-Step Guide

Troubleshooting Your AC: Testing the Compressor Clutch Coil

The compressor clutch coil is crucial to your vehicle’s air conditioning system. When it malfunctions, your AC may stop working entirely. Here’s how to diagnose and test a compressor clutch coil.

If your car’s AC compressor clutch won’t engage and low side and high side pressures are within specifications, follow these instructions to test the compressor clutch coil.

Test the clutch coil for resistance and opens

Disconnect the electrical connector to the clutch coil and use a DVOM set on the Ohms scale. Touch the probes to the clutch coil terminals. The average clutch coil resistance is 3Ω to 5Ω. Readings less than 2Ω or greater than 5Ω mean the clutch coil is bad.

Check for battery voltage and ground at the clutch coil connector

Unplug the connector to the AC clutch coil. With the engine running and AC in MAX

AC compressor clutch connector

position, set your DVOM to DC volts, and back probe the positive side of the clutch coil connector. You should see battery voltage. Next, connect one probe of your meter to the positive terminal in the connector and the other probe to the ground connector. Once again, you should see battery voltage. These tests confirm that the clutch coil is receiving full battery voltage and good ground. It also confirms that the HVAC control, fuse, and relay are working properly.

Next, perform a voltage drop test on the clutch coil

Plug the connector into the clutch coil. Set your DVOM to DC volts. Connect one-meter lead to the negative battery post and use the other lead to back probe the positive wire in the clutch coil connector. Start the engine and set the AC to Max. The voltage drop should be less than 1 volt. Higher readings mean excessive resistance in the circuit between the battery and the compressor clutch.

Set your DVOM to DC volts. Connect one lead to battery NEGATIVE post and the other lead to the NEGATIVE terminal of the clutch coil connector. The voltage drop should be less than 0.2-volt. A higher readings means excessive resistance in ground circuit to the compressor clutch coil.

©. 2018 Rick Muscoplat