Why is there a knocking noise when the a/c is on? on 2008 Nissan Altima

You only hear the knocking noise from time to time and it is only when you come to a complete stop. You turn the a/c off and the noise stops.

Asked by for the 2008 Nissan Altima
1 answer
poss compressor is going bad due to lack of oil,have it ck"d