AC question
Thread Starter
3rd Gear
Joined: Jul 2008
Posts: 3
Likes: 0
AC question
I previously posted: I own a 1995 Corvette with standard A/C. The air flow thru vents diminish in volume after about 1 hour of driving, although the fan still runs at all speeds. You can hear the fan running, but the air flow is diminished. If we shut the car off and start it again, the air flow is fine for about an hour before it diminished. Any ideas what is causing this problem? Any ideas how to fix it? Thanks for the help - A couple of people suggested the evaporator was freezing up (I was thinking this also) -- so.... 1 -What causes the evaporator cord to freeze and 2 - Does low refrigerant cause this to happen. Thanks again for all your help in solving this problem
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
System is designed to shutoff if the pressure of the refrigerant is low enough to make ice. It does that via a switch - the Low Pressure Switch - which simply opens the ground to the compressor circuit. If that switch has failed, it can make ice.
First you need to confirm what it's doing and the best way to do that is to hookup a manifold gage set. If you haven't done this or can't do that, go to an a/c shop and have them pressure test your system. And make sure that whomever does this - or if you do it yourself - that the Blower Motor connector gets disconnected while the system is set to Max. That will drop the Low Side and the compressor should cutoff at 22.5 psi (R134) or 25 psi (R12). If it doesn't, the switch is bad or you may be able to adjust it so that it works again. You can post whatever you find out including the Low and High Side Pressures here or on an a/c board such as the one run by www.ackits.com for additional help. Or, if you simply want to, you can replace that Switch and see if the problem goes away. I'd rather be sure, but these Switches don't cost much and it's simply a matter of unscrewing the old one (really fast so the charge doesn't escape) and screwing the new one on. The switch is mounted on the Evaporator outlet line - that's the big one at the top and the Evaporator is in that case poking out from the passenger's side firewall.
First you need to confirm what it's doing and the best way to do that is to hookup a manifold gage set. If you haven't done this or can't do that, go to an a/c shop and have them pressure test your system. And make sure that whomever does this - or if you do it yourself - that the Blower Motor connector gets disconnected while the system is set to Max. That will drop the Low Side and the compressor should cutoff at 22.5 psi (R134) or 25 psi (R12). If it doesn't, the switch is bad or you may be able to adjust it so that it works again. You can post whatever you find out including the Low and High Side Pressures here or on an a/c board such as the one run by www.ackits.com for additional help. Or, if you simply want to, you can replace that Switch and see if the problem goes away. I'd rather be sure, but these Switches don't cost much and it's simply a matter of unscrewing the old one (really fast so the charge doesn't escape) and screwing the new one on. The switch is mounted on the Evaporator outlet line - that's the big one at the top and the Evaporator is in that case poking out from the passenger's side firewall.
