knocking sound when a/c is on

[xeanerix20]

has anyone here experiencing something like this to their car? my problem is when the engine is running and i switch on the a/c and revs the engine, everytime i let go of the accelerator there is a knocking or topping sound coming from the engine bay. i tried it when the bonnet is open and try to listen where its coming from, and it sounds like coming from somewhere near the aircon compressor but really not sure if it's the compressor or from the engine. even when the car is on the road and the a/c is on, everytime i decelerate i can here and feel it. but when the a/c is off i don't hear that knocking sound. please help, 'coz it's really annoying. i hope it's not the engine.

[accentstencil]

If it is not the compressor then maybe it is a worn harmonic balancer, the added load with the compressor on could be the reason it only does it with the A/C on. Check the condition of the rubber in the centre of the balancer, check for cracks or missing pieces of rubber. If you don't know where the harmonic balancer is, it is the big pulley at the bottom of the engine.

[brad_m_is]

yeah mate my compressor just started doing the same thing it still works perfectly so im not going to wory until it dies. put ur hand on one of the rubber pipes going into the compressor and rev the engine mine gives a knocking as the revs just about return to idle