Heater A/C Problem
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Joined: Dec 2002
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From: Everett WA
Heater A/C Problem
I've got an 87 with the electronic heater A/C controls. No matter if I have the heat or A/C on, I'm getting air out of both the heat and A/C vents. Shouldn't it be one or the other? What should control the switching between the vents? I've looked in the archives, but couldn't find this one. Thanks for the help!!
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Re: Heater A/C Problem (87Vert)
Should be a small amount of cool air out of the heater vents with a/c on and a similar amount to the side window defoggers. With heat, all of the air should be through the floor vents. Programmer controls the position of the air doors and it operates off of vacuum from the plenum (next to fuel pressure regulator). Follow that line to a check valve (near the distributor) and make sure that the line and the valve are in good shape. Make sure the line from the valve through firewall to the Programmer is in good shape too. Also check the vacuum tank in the left front fender well below the headlight and that it's line is intact and that the tank can hold vacuum. Otherwise, suspect the Programmer. It's above and to the right of the accelerator. Access by removing the hush panel.
Le Mans Master
Joined: Jul 1999
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From: Maryland
Re: Heater A/C Problem (SunCr)
This is gonna sound wierd, but does your cruise control work? There's a vacuum line on the underside of the runner thing. If it comes off cruise is inoperative. When I got new vac lines for mine my inoperable vent doors and AC suddenly started working along with the cruise control. ;)
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From: Everett WA
Re: Heater A/C Problem (oldace84)
Thanks for the suggestions! I didn't really know where all the vacuum lines were. Cruise control does work, but I'll still check all the lines in the area. How do I check the vacuum tank?
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Re: Heater A/C Problem (87Vert)
With a vacuum gauge (you need an adaptor) disconnect the inlet and check for vacuum on that line. Plug it back in and check for vacuum on the outlet side of the tank. If none on the outlet, tank is bad.
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Joined: Dec 2002
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From: Everett WA
Re: Heater A/C Problem (87Vert)
Ok. I've chased all the vacuum lines I could find and they all seem to be good. The big sherical gizmo in the front left holds vacuum (although I have no clue how it works or what it really does). I can not find where a vacuum line penetrates the firewall. I think I found the one that's kinda behind the distributor with some sort of check valve on it, but I couldn't see where it goes after it drops behind the distributor. I took off the cover under the steering wheel to look for the programmer thing, but all I saw was wires wires everywhere! I could see no vacuum line that was apparent to me. (I do not have a GM Shop manual. Is any of this stuff described in there?) Any other suggestions?? :(
Race Director
Joined: Sep 2000
Posts: 12,182
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From: Partying with the Cowboys cheerleaders in Mt. Olive, New Jersey
Re: Heater A/C Problem (87Vert)
Sounds like a check valve problem to me... it's located next to the distributor. By the way, do get a shop manual. It's so worth the money it's not even funny. Good luck.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Re: Heater A/C Problem (87Vert)
Vacuum tank holds vacuum during acceleration for continous operation of cruise and a/c. There is a vacuum harness on the front of the programmer and it can be a bear to get off. If you want to see if there's vacuum to the progammer, remove it and then unbolt the harness. Check for vacuum on the black line. If it's there the programmer is probably bad. Otherwise, the check valve, is the most likely culprit.