A/C Heater control vacuum problem
Thread Starter
Race Director
Joined: Dec 2000
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From: El Paso Texas
A/C Heater control vacuum problem
84 Corvette
Driving home today, My A/C is ice cold, but the air started coming out equally from all vent openings (dash, floor, defrost) regardless of switch position. I first suspected that the A/C heater control head had failed, but when I removed it and started the car, I can't feel vacuum coming out of any of the lines. This leads me to believe that I've lost the vacuum source for the controller.
I have the factory shop manual, which has the vacuum diagrams. On my next day off, I'm going to get a vacuum pump and start testing everything, from the cannister back, to make sure it holds vacuum. I also figure I should just go ahead and replace all the interior lines that control the dampers.
Sooooo......here's my question: How do I access the vacuum motors that control the interior vent doors? Do I have ample access if I remove the dash pad? Any advice? I would like to test all the vacuum motors while I have it apart and replace anything faulty.
TIA ......
Friz
Driving home today, My A/C is ice cold, but the air started coming out equally from all vent openings (dash, floor, defrost) regardless of switch position. I first suspected that the A/C heater control head had failed, but when I removed it and started the car, I can't feel vacuum coming out of any of the lines. This leads me to believe that I've lost the vacuum source for the controller.
I have the factory shop manual, which has the vacuum diagrams. On my next day off, I'm going to get a vacuum pump and start testing everything, from the cannister back, to make sure it holds vacuum. I also figure I should just go ahead and replace all the interior lines that control the dampers.
Sooooo......here's my question: How do I access the vacuum motors that control the interior vent doors? Do I have ample access if I remove the dash pad? Any advice? I would like to test all the vacuum motors while I have it apart and replace anything faulty.
TIA ......
Friz
Thread Starter
Race Director
Joined: Dec 2000
Posts: 17,551
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From: El Paso Texas
Originally Posted by comp
i think so , doesn't the book show it???
Anyone?? Somebody must have done this before.
Intermediate
Joined: May 2004
Posts: 36
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From: Southern Pines NC
I just noticed you have a 84. I posted the following as I had the exact same problem with a 96. Hope it helps... from my searches in the archive when I was fixing the same problem, it seems the HVAC programmers in all C4's die with some regularity.
if you have no vacuum at the programmer (located on the firewall above the accerator pedal) likely the vacuum supply valve (really a tee fitting) located under the passenger side fuel rail cover (between intake and head on engine) has melted-rotted-cracked. This part is only $5-6 from your local Chevy dealer. Try this 5 mn fix first.
I had the same condition and the problem was two fold. The connector behind the dash control head was dirty causing the lights on the dash control head not to illuminate/work. Second, the quick connector at the HVAC programmer for the 5-6 vacuum lines was leaking. There are no parts available to repair the connector and a new programmer from GM is $907 for a 96 with C-68 auto-air option.
Look under tech tips for a good post on how to repair your programmer. It almost worked for me, but I ended up having to replace the programmer with a used one for around $100.
if you have no vacuum at the programmer (located on the firewall above the accerator pedal) likely the vacuum supply valve (really a tee fitting) located under the passenger side fuel rail cover (between intake and head on engine) has melted-rotted-cracked. This part is only $5-6 from your local Chevy dealer. Try this 5 mn fix first.
I had the same condition and the problem was two fold. The connector behind the dash control head was dirty causing the lights on the dash control head not to illuminate/work. Second, the quick connector at the HVAC programmer for the 5-6 vacuum lines was leaking. There are no parts available to repair the connector and a new programmer from GM is $907 for a 96 with C-68 auto-air option.
Look under tech tips for a good post on how to repair your programmer. It almost worked for me, but I ended up having to replace the programmer with a used one for around $100.
Last edited by NC LT4; Sep 7, 2004 at 01:04 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
All '84's were manual air, so it doesn't have a Programmer - just the Control Head or Dash Assembly which you've allready checked.
There should be 3 solenoids mounted on the Heater Box, usually on the left side above the accelerator. Remove the driver's side hush panel to gain access. Universally, GM uses a Red/Tan lines for Defrost; a Dark Blue for the Front (a/c); and Pink for the Rear (Heat). There is probably a 4th solenoid for outside air. It should have an orange line and is usually mounted on the passenger's side, upper kick panel.
Do check the source. An inoperative solenoid wouldn't drain vacuum from the dash control. GM uses a check valve to keep vacuum from bleeding off. Should be connected to the source, before the firewall. Once you find it, make sure air only flows in the direction of the dash assembly.
There should be 3 solenoids mounted on the Heater Box, usually on the left side above the accelerator. Remove the driver's side hush panel to gain access. Universally, GM uses a Red/Tan lines for Defrost; a Dark Blue for the Front (a/c); and Pink for the Rear (Heat). There is probably a 4th solenoid for outside air. It should have an orange line and is usually mounted on the passenger's side, upper kick panel.
Do check the source. An inoperative solenoid wouldn't drain vacuum from the dash control. GM uses a check valve to keep vacuum from bleeding off. Should be connected to the source, before the firewall. Once you find it, make sure air only flows in the direction of the dash assembly.
Thread Starter
Race Director
Joined: Dec 2000
Posts: 17,551
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From: El Paso Texas
Originally Posted by SunCr
Do check the source. An inoperative solenoid wouldn't drain vacuum from the dash control. GM uses a check valve to keep vacuum from bleeding off. Should be connected to the source, before the firewall. Once you find it, make sure air only flows in the direction of the dash assembly.
Thanks a million Sun. So far, here's what I've got.
The check valve by the firewall flows both directions, so it's apparently bad. But I also don't have any vacuum entering the inside of the car either. I removed the check valve and plugged the source line going into the car, and tried to pull a vacuum on the black source line from inside the car....nothing. So it appears there is a leak in that line. The other lines that go to the vacuum valves all hold vacuum, and appear to operate correctly.
I going to run a temporary supply line outside the car to the control head and see if this makes everything work. If so, I will have to run a new supply line.
The supply line looks like it enters the firewall under the passenger hush panel. Is this correct?
It also looks like the source line is encased in the black plastic conduit that carries wiring, which means it will be loads of fun to snake a new line through it.
Thanks again everyone for the input.
