Rick's Free Auto Repair Advice

Car AC compressor noise

What causes car AC compressor noise?

I often see questions on auto forums where the posters ask about car AC compressor noise when they use their AC. Here are the most common AC noises.

AC compressor noise — Squeal or screech when the compressor engages

Ac Compressor Belt issues

This noise is most often due to too little tension on the AC belt. The squeal is caused by the belt slipping around the AC compressor pulley. See this post on how to test to see if the problem is caused by a tension issue.

In addition to too little tension, a squeal can also be caused by a worn drive belt. Modern multi-groove EPDM drive belts don’t crack like older neoprene belts, so you can’t judge wear visually. You must use a wear gauge. When EPDM belts wear out, they no longer drive the pulley with the multiple “V’s,” instead they drive the belt from the backing of the belt and that can create a squealing sound. Check the drive belt for wear. See this post for more information on drive belt wear.

AC compressor clutch issues

A squeal or screech can also be caused by a worn AC compressor clutch disc. An AC compressor clutch relies on a metal clutch disc being pulled into contact with the AC pulley by the magnetic field created by the clutch coil. If the clutch coil magnetic field is weak due to internal breakdown the clutch disc will slip causing a high pitched metal-to-metal screech.

The same noise can be caused by an excessive air gap between the pulley and clutch disc that prevents even a good clutch coil from being able to pull the clutch disc into contact with the pulley. Check the clutch coil resistance voltage and ground connection. Also, measure the clutch air gap. See this post for more information on clutch air gaps.

AC refrigerant charge issues

A less common cause of AC compressor noise is an overcharged system. When a car AC system is overcharged, the high pressure tends to lock up the compressor, causing even a properly tensioned drive belt to slip and cause a squealing noise. See this post for more information on AC pressure gauge readings

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