Jim Grant's Tech Tips

‘96 Chevy Lumina Van, A/C Knock
Q: I have a ‘96 Chevy Lumina Van with a 3.4 DOHC. My concern is when the A/C is on the engine makes a knocking type noise. This noise appears to be coming from inside the engine and goes away when the A/C is turned off. The engine's idle or driveability isn't affected by this knocking. Could this be the beginning of something bad?....Jason

A: I have no reason to believe that there is an engine problem. The first item I’d suggest checking would be the A/C compressor or the mounting bracket for the compressor for loose bolts. If either has loosened up, it doesn’t have to be by much, a knocking noise can occur when the A/C compressor is on. If the compressor and mount are tight then the A/C compressor itself would become suspect.