PontiacBonnevilleClub.com

Issue: The car blows cold air when it should be hot air, with the exception of a fresh startup, it'll blow hot air for 1-10 minutes. If you turn the temp down and back up, it'll be cold air.

Car History: I just bought the car with 130k on it. It had already been converted to EG (green) coolant. It looked pretty old, so i did two "drain and fills", out of the radiator only. I burped the air out of the system, and it seems to be functioning perfectly. Never tried to use the heat prior to doing this, no idea if it worked correctly before.

Other knowns:
- the temp gets to 195* and stays there, perfectly normal
- both heater hoses are very hot, heater core not plugged
- car has dual zone CC, both sides act the same. Eliminating an air-mix actuator from the potential causes (i think).
- AC blows perfectly cold

Thoughts? I don't know the HVAC system well enough to diagnose.

Side question - is there a way to tell if the LIM gasket has already been changed? Any sign? The part of the gasket I can see is black...

I did some more goofing around with it and got some more information that may help figure it out.

-If you start the car with the heat on (90*), it will run with full heat as long as you want it to.
-If it's blowing hot air, you can turn the unit completely off, and back on and it will still blow heat.
-If you turn the temp down, then try to turn it back up... it just blows cold air.
-If you turn the car off, and start it back up... it'll blow hot air again.
-As long as one side is still at 90*, it will still blow hot air. I can turn one side down to 60, and leave the other at 90 and one will blow cold, and the other hot.

It seems like it has no problem blowing heat, but as soon as you turn it down something gets stuck and has to reset...

That is interesting. Perhaps the doors, or actuators get stuck when they get hot. Can you watch the actuators to see what they are doing, or not doing, when it messes up?

If you can see black with the LIM gasket, they probably have not been changed. The new ones are a gray/aluminum color. There's a picture of them in this techinfo article.
http://www.pontiacbonnevilleclub.com/fo ... =53&t=3591