Greetings fellow forum members,

I have a 2005 Volvo S40 1.6D and I just noticed that when I rev it past 2k rpm, a rattling sound is heard from the right side of the vehicle. Being an old 4 cyl diesel it's pretty noisy after 2k rpm but this rattle definitely isn't normal engine noise. At first I thought the rattle is coming from some lose interior trim since the car is 17 years old but I had discovered that it only occurs when the AC is on. Turn the AC off, sounds normal, turn AC on and the rattle appears. I can't seem to replicate it by reving the engine while stationary, only while driving.
One more thing, I found that when the AC is on, the sound of the car becomes different, I know that the AC robs a lot of power from the engine and that the engine needs to work harder to keep it running but when the AC is on a thumping noise can be heard in addiotion to normal engine noise. Same thing, turn off AC the thumping goes away.
Any suggestions?

Thank you!

 

Possible causes for an AC rattle: failing compressor, worn bearings in serpentine belt pulleys/idlers, worn serpentine belt, worn compressor clutch (ie bearings again) - on some cars the clutch can be replaced separately from the compressor...

 

Yes at that age and only when AC is on must the AC compressor , when the AC is off the belt turns but the clutch on the compressor disconnects the AC compressor , so sounds like its the compressor when under load