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How to Test an AC Clutch Coil

by Jack Hathcoat

The A/C compressor is the heart of the system, and without a good compressor, the unit will not function. The compressor is engaged by the compressor clutch, made up of a powerful electromagnet and a drive plate. You'll hear a distinctive click when the compressor is energized as the drive plate is pulled into place. The electromagnet does not rotate like the clutch does. It is bolted into place on the front of the compressor.

Examine the A/C clutch with a flashlight. In almost every instance when the clutch fails, it becomes burnt and discolored. The flexible, rubber isolators that allow the clutch disc to move in and out will melt from the intense heat, and the metal plates will appear rusty. In these instances, replace the compressor assembly.

Unplug the compressor connector. Install jumper connectors onto the compressor electromagnet. Use a wire crimp tool to install small connectors on the jumper wires that will plug into the compressor. This is important because the pins on the compressor connector are small, so select connectors that will fit in the compressor plug and not short out by touching each other.

Route the wires directly to the vehicle battery. Connect one of the wires, it doesn't matter which one, to the negative side of the battery. Touch the other wire to the positive side. If the magnet is good, the compressor clutch will click into place when the magnet powers up. Release the clutch by removing the positive wire. Repeat this procedure several times, each time listening for the clutch to energize. If the magnet is defective, replace the compressor.

Warning

  • If the clutch coil shorts out, the positive wire may begin to heat when it touches the positive battery post. If this happens, quickly remove the wire and replace the compressor. This could also happen if the two, small connectors are touching each other. Be certain and use the right sized connectors to conduct this test.

Items you will need

References

About the Author

Jack Hathcoat has been a technical writer since 1974. His work includes instruction manuals, lesson plans, technical brochures and service bulletins for the U.S. military, aerospace industries and research companies. Hathcoat is an accredited technical instructor through Kent State University and certified in automotive service excellence.

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