jacal128

Took the 86.5 out for a drive earlier, still a little warm so I ran the AC. It started a hissing sound, kind of a depressurizing sound and not so much a vacuum leak. It vary in sound but not with the engine speed. The sound is a great deal like a condensing unit going into defrost mode. Everything still blowing cold no odd smells just a new sound. I was planning on cracking into the console in a couple of months but might need to do it sooner. Any ideas would be greatly appreciated. Thanks, Jack

dprantl

Does it hiss more/louder when you raise the RPM? If yes, it is probably low on refrigerant. The leak could be anywhere, so I would start in places easier than inside the dash.

Dan
'91 928GT S/C 475hp/460lb.ft

jacal128

It's not RPM based, it seems to kind of raise and lower on its own sometimes it will just stop.

dprantl

It is normal for the expansion valve in some systems to hiss when you first turn on the A/C. It should be momentary and then subside. It can reoccur if the anti-freeze switch temporarily shuts off the compressor due to the evaporator getting cold enough, but upon compressor engagement again the hiss should be relatively short and subside. If the hiss persists, there is not enough refrigerant in the system and there is a leak somewhere. The hiss does not denote the leak though. If the leak was that large as to emit an audible hiss from inside the car, all the refrigerant would be gone in several minutes.

There is also the possibility that one of the vacuum pods for the climate control are failing, but those usually don't hiss, but make flapping noises.

Dan
'91 928GT S/C 475hp/460lb.ft

griffiths

You may want to poke around and see if the noise is coming from a certain area,
say for example if the noise is in the cockpit rather than the engine compartment, see if its coming from the RH side, center or LH side of the dash. Does the noise come and go when you change the temperature of the ac control? Determine the location.

jacal128

It sounds exactly like the expantion valve noise, but it kind of rises and lowers in intensity but never really going away. I will poke around and see if I can see any signs of a leak and will let you know. Thanks Jack

WallyP

With engine running. A/C on so that you hear the hiss, step outside and disconnect the tiny vacuum line from the brake booster valve. This should completely kill the vacuum inside the car. Wait a couple of minutes for the vacuum reservoir to fill. If you still hear the hiss, it is A/C. If the hiss disappears, it is a vacuum leak.

Reconnect the vacuum line.