HVAC Programmer/Temp Door Fixed!

[Chris Kennedy]

Well, I am pleased to report that the temperature door on my '89 Ebay rat is now fixed after much study and many questions (it wasn't working when I got the car, notwithstanding the claims of the electrical engineer who said it was fixed by him----go figure). The problem was that, as I suspected, the HVAC programmer was bad. I replaced the programmer with a new one from gmpartsdirect.com this weekend, and gritted my teeth as I switched the controller from full air conditioning to full heat. Voila! It was one those triumphal moments that I am sure you can all appreciate. So, the lesson is this: If everything works on the electronic HVAC system except that the temperature door does not swing from full by-pass of the heater core to flow through the heater core, then the problem is probably the HVAC programmer. From some tests I ran it also appears that the temperature door does an automatic default to full by-pass of the heater core if the programmer is defective. Here in Houston, it was 80 degrees yesterday, so the rat and I went down to Galveston to go surfing and we ran into a dense fog bank (virtually no surf and no visibility cancelled surf plans). The outside temperature dropped about 15 or more degrees within three miles from the beach, so I got a chance to try out the heater for real. It seems to work great!

/s/ Chris Kennedy
Houston, Texas

 

[Agent 86]

Good way to start the new year

 

[aboatguy]

I am glad to hear that someone was able to fix a C4 HVAC problem. I just hope mine never goes out.

Mike

 

[Chris Kennedy]

I am glad to hear that someone was able to fix a C4 HVAC problem. I just hope mine never goes out.

Mike

Don't worry if it does go out, as it was surprisingly easy to change (I had all sorts of worries, too, that the thing would be innacessible, even though I am a limber guy and could squeeze myself under the dash pretty well). You simply take off the under dash panel, and the box is located just to the right of the steering column against the firewall. It is held to the firewall by one small screw which is right in front of you and easy to reach and tabs at the top end of the box fit into something I couldn't see. You simply take out the screw and slide the box down, and unplug the vacumn lines block, the electrical connection, and unscrew some other thing on the box I couldn't figure what it was, and reverse the process with the new box. Luckily (since you can't see what the tabs at the top go into), you sort of slide the box up against the firewall until the screw hole on the box is lined up with the screw hole on the firewall (that causes the tabs to lock in). I wouldn't worry about trying to fix the old unit, but instead contact either gmpartsdirect.com for a new one or Corvette Central for a new or rebuilt one. They both have by far the best prices (my new box cost $117). One other thing I'd recommend is to have plenty of light. I bought one of those battery powered florescent floodlight type things, which was lousy, so what I did was to un-snap the electrical connection last so that I could keep the battery connected as long as possible to use a terrific portable light I have before having to resort to the floodlight, and first re-connect the electrical connection on the new box so that I could re-connect the battery and go back to my good light. Anyway, the entire replacement took me about an hour and a half, so if you have a mechanic do it don't let them b.s. you about "oh my God, it is SO impossible to do it except for some exhorbitant sum," etc etc etc...You know what whiners these so-called Corvette experts are.

/s/ Chris Kennedy

 

[aboatguy]

Don't worry if it does go out, as it was surprisingly easy to change (I had all sorts of worries, too, that the thing would be innacessible, even though I am a limber guy and could squeeze myself under the dash pretty well). You simply take off the under dash panel, and the box is located just to the right of the steering column against the firewall. It is held to the firewall by one small screw which is right in front of you and easy to reach and tabs at the top end of the box fit into something I couldn't see. You simply take out the screw and slide the box down, and unplug the vacumn lines block, the electrical connection, and unscrew some other thing on the box I couldn't figure what it was, and reverse the process with the new box. Luckily (since you can't see what the tabs at the top go into), you sort of slide the box up against the firewall until the screw hole on the box is lined up with the screw hole on the firewall (that causes the tabs to lock in). I wouldn't worry about trying to fix the old unit, but instead contact either gmpartsdirect.com for a new one or Corvette Central for a new or rebuilt one. They both have by far the best prices (my new box cost $117). One other thing I'd recommend is to have plenty of light. I bought one of those battery powered florescent floodlight type things, which was lousy, so what I did was to un-snap the electrical connection last so that I could keep the battery connected as long as possible to use a terrific portable light I have before having to resort to the floodlight, and first re-connect the electrical connection on the new box so that I could re-connect the battery and go back to my good light. Anyway, the entire replacement took me about an hour and a half, so if you have a mechanic do it don't let them b.s. you about "oh my God, it is SO impossible to do it except for some exhorbitant sum," etc etc etc...You know what whiners these so-called Corvette experts are.

/s/ Chris Kennedy

Changing/replacing the controller doesn't worry me. I keep reading threads where guys have changed the controller, checked the vacuum lines and the HVAC continues its faulty operation.
Once again congrats.

Mike

 

[elroys]

From personal experience with an '89:

The controller usually goes bad because two under rated resistors overheat and burn out over time. This condition will cause the heater vent's motor to continually run and eventually its plastic gears will strip (if not caught soon enough). The duct is then stuck open.

So there may sometimes actually be 2 problems and if both are not repaired the problem continues (heat from vent would not turn off).

I replaced the two resistors and the motor/gear assembly. All is well.