AC compressor seized or won't turn

Symptoms

• AC compressor pulley doesn't spin even though the belt is on and tight
• Loud squealing or the engine bogging down when AC is turned on
• Serpentine belt may show burn marks or have snapped
• AC hasn't worked at all recently, possibly with prior noise

Likely causes

• CommonInternal compressor seizure from lack of lubricationRunning low on refrigerant (which carries the compressor's oil) for a long time can starve internal parts of lubrication until they seize.
• CommonInternal mechanical failure (broken piston, scroll, or bearing)Age and wear can cause internal components to fail and lock the compressor solid.
• PossibleClutch bearing seized (not the compressor itself)Sometimes only the outer clutch bearing seizes while the compressor internals are fine, which is a cheaper fix if diagnosed correctly.

What to do

1. Turn off the engine and try to turn the compressor pulley by hand (carefully, engine off and key out) to confirm it's truly seized versus just not engaging electrically.
2. Inspect the serpentine belt for damage, burn marks, or breakage, since a seized compressor can destroy the belt quickly and affect other components it drives.
3. Do not run the engine with a seized compressor still connected to the belt, since this can snap the belt (losing power steering, alternator, or water pump function) or damage the engine.
4. If the belt is intact and the pulley won't turn, treat this as an urgent repair rather than continuing to drive, especially if other accessories share that belt.
5. Have the compressor replaced by a shop, since seized units require full system flushing to remove metal debris before installing a new compressor and recharging.

Tools and parts

When to call a pro

See a mechanic promptly; a seized compressor on the accessory belt can affect other critical systems if the belt fails, and the compressor itself needs replacement along with a system flush.

Safety