I have a 1999 f150 4.6L 5 speed and have a high pitched squell under the hood. Only does it at high RPM's. it doesn't change with the ac on or off. Ac works great and blows cold. No loss of cold air when squell is happening. Squells less or not at all in cold weather. I can't tell if it's the alternator or something else. Tension pulley has been replaced in the last 5 years. If it is the ac clutch pulley is the pulley replaceable or do I have to get a whole new compressor? Any thoughts would be appreciated.

 

The best way to tell is to pull the belt off and spin everything by hand. It should be quiet and smooth. AC clutch is replaceable. If your belt is in rough shape replace it too.

 

Thanks. I'll try that first.