my a/c compressor is making a loud hissing noise (bearings maybe) when the a/c is off but when you turn it on it stops??? also the compressor isn't cycling like it should, it just stays on all the time then it eventually will stop blowing so you have to turn it off for 3 or 4 mins then turn it back on and it'll work again. i've changed the pressure switch and it still doesn't cycle...what's the deal??? thanks