A/C vents problem
Thread Starter
Instructor
Joined: Jul 2009
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A/C vents problem
OK heres the problem, at idle 700 rpm my A/C blows out loads of cold air, however above 1500 rpm the pneumatic vents appear to close as the force of cold air drops off. If I ease off the gas the air returns with more force. I assune more RPM means more vacuum and hence the vents should be wide open, however they appear to be closing...Any ideas???
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
You should state year.
I wrote this up awhile back.
On at least later C3 the problem is that heater is the default position (no vac. or vac. leak) due to being designed in the north. Vent should be default.
1) The vac. line from engine may be damaged from heat - a small plastic tube that goes in below the hood alarm switch into wiper valley. Replacing most of engine side w/ hose will fix.
2) The vac. switch itself is not switching due to vac. leak as the usually plastic rivet is not holding the 2 main switch parts together well. Besides replacing, it is also possible to tighten this &/or lube w/ a thin layer of white lithium grease to fix.
3) If you have a heater, the small vac. tube to heater hose valve underhood may be damaged from heat & need replacing. Block w/o heater.
PS The design problem comment is not intended to be offensive to any of our northern friends.
I wrote this up awhile back.
On at least later C3 the problem is that heater is the default position (no vac. or vac. leak) due to being designed in the north. Vent should be default.
1) The vac. line from engine may be damaged from heat - a small plastic tube that goes in below the hood alarm switch into wiper valley. Replacing most of engine side w/ hose will fix.
2) The vac. switch itself is not switching due to vac. leak as the usually plastic rivet is not holding the 2 main switch parts together well. Besides replacing, it is also possible to tighten this &/or lube w/ a thin layer of white lithium grease to fix.
3) If you have a heater, the small vac. tube to heater hose valve underhood may be damaged from heat & need replacing. Block w/o heater.
PS The design problem comment is not intended to be offensive to any of our northern friends.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The more rpm, the more open the throttle, so the vacuum is lower. You have a vacuum leak in your system somewhere. At idle [when vacuum is at maximum], your A/C control system works OK; once vacuum decreases, you have your problem. A small leak in the vacuum system can be tolerated at idle...but not at higher rpms. Get a troubleshooting manual for the vacuum system & a vacuum gauge; then search out the leak and fix it.
The solution could be as simple as the check valve being defective...but there are lots of other potential causes, too. Trying 'this' and trying 'that' is an inefficient problem solving approach. Attacking it with knowledge and logic is much more effective.
The solution could be as simple as the check valve being defective...but there are lots of other potential causes, too. Trying 'this' and trying 'that' is an inefficient problem solving approach. Attacking it with knowledge and logic is much more effective.
Last edited by 7T1vette; Oct 20, 2009 at 09:11 AM.
Thread Starter
Instructor
Joined: Jul 2009
Posts: 155
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Thanks guys, I have a 1982 Crossfire running with X-Ram intake. I just replaced my A/C control levers as one had snapped in two. When I was in there I found the vacuum switch totally bypassed, I mean someone had physically hard wired it so to speak, picture attached. I inspected the switch as I had read about the thing coming apart and it looked good and tight so I re-assembled it correctly. If I understand correctly I am losing vacuum to the vents and need to find the cause of the leak / low vacuum.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Yes you are looking for a vac. leak. Guess why someone would bypass a switch that commonly leaks when it gets old- so it needs to be checked very carefully. Check the switch for leaking by starting engine & listen for vac. leak & test. If it does not work correctly, press the 2 halves of the switch together & test.
The vac. opens some vents & closes others, for ex. vac. opens the center A/C vent & closes the heater vent.
The vac. opens some vents & closes others, for ex. vac. opens the center A/C vent & closes the heater vent.
