When I turn on my defroster , I hear a loud noise in my engine
compartment . on 1994 Mercury Tracer

I have been told that it could be my air conditioner compressor,but I hear the noise when I turn on my defroster or air circulation . Is the air compressor required for all air functions?

Asked by for the 1994 Mercury Tracer
The AC compressor does run in defrost mode, so you may have been told right! Hear it in floor mode?