HVAC Problem

[Bisha]

I have a '06 auto coupe. This is an intermittent problem that has happened twice so far and I know it will again so I am trying to get ahead of it. The passenger side of the car will suddenly start blowing very hot air from the vents no matter what setting the hvac system is on. I live in Florida so the A/C is almost always on even in cool weather due to the humidity. When this happens I get normally cool air on the drivers side and very hot air on the pass side. It does not matter if the system is set to use only the driver master control of if the pass side control is activated. I have tried switching temp extremes from 60 to 80 and it has no effect of the pass side but works normally on the drivers side. My fix has been to turn the system off and on and to repeatedly cycle the system through all its various settings, thus forcing all the vents to repeatedly open and close. Eventually the system will come back to normal operation. It is obvious from the high pass side temp that the heat is on maximum for that side. I have tried the so-called soft reboot (pressing fan speed up/defrost/rear defog) and that had no effect. I have the service manual for the car and have found nothing to give me a clue. It am guessing that some actuator is malfunctioning or some door in the system is intermittently stuck open. I appreciate any help, thanks!

It happened again this afternoon and I reread the manual. It said that pulling the HVAC main fuse out for at least 60 sex would reset the HVAC Control Module. Did this and it seemed to fix the problem so far. If anybody has any long term suggestion I would appreciate it, or maybe theModule just gets out of whack sometimes and this will become a maintenance as needed item.

[TheRobSJ]

Pulling the fuse does reset the system. It forces the system to "relearn" all the door positions by sweeping them their entire range. This takes 30 seconds or so for the system to relearn, and then it sets everything according to the requested temp(s) and mode.

If this problem occurs again, don't pull the fuse. Have the system scanned for a trouble code. Hopefully one will be stored that can give the technician diagnosing it (or us here) an idea of what part is failing.

[Bisha]

Thanks for the advice. I have been thinking about buying a code reader and there are many on the market. Any suggestions for a good one that is not too expensive? They all seem to do about the same thing and there is a wide range in price.

[TheRobSJ]

Unfortunately, many of not all of the inexpensive ones only read codes for the powertrain (P0300, P0455, etc). You would want something that has enhanced GM capability so you can read codes in some of the other modules too. Namely the body control module and for your specific problem, the HVAC module.

[c6vette]

See the thread "BCM Flash" dated 12 -13-09. (C6vette response) It may be the answer to your problem.