My a/c was working fine, then I shut it off for about 1/2 hr. and when I turned it on again it only blew hot (engine?) air. It has ECC and I tried using manual settings and still hot air. After the car sat for about 2 hrs. the a/c started blowing cold again. Now, it'll even be cooling properly and suddenly the air starts coming out hot - without shutting anything off. The fan works fine, it's just that it doesn't blow cold air consistently. It's obviously not out of freon (a/c coolant) because sometimes it is cold. Any suggestions on where to start looking would be greatly appreciated!