2005 Chevy Uplander Heater blowing cold Air

  • 6 CYL
  • 2WD
  • 40,000 MILES
We have a 2005 uplander with hot air heater problems. Start the vehicle for the 2nd time. No hot air, vent selector switch working(set on hot), blower motor switch is working, engine temp good, coolant good, fuse good. When changing functions we could here the switching. Played wtih fan switch and heater switch. Turn van off. Restart play with switches again. All of sudden heat enters the cabin. Happens every 3rd or 4th time the vehicle is used. Taken to dealership. Everything checked out electrically when the heater is operating normally. They suggested replacign the thermostat. Issue did not go away. This can be an expensive endaveour to route casue the issue. I am in contact with the electrical engineer from GM on the program. I post what he finds out regaqrding this issue.

Found the solutuion to the problem. There is a software issue with HVAC module may be exhibiting "Temperature Door Drift". The result of the investigation was a new release of software for service into GM SPO.

Problem statement: GM 2005-2006 Minivan vehicles while operating in full cold mode, the discharge temperature of the supply air stream is not sufficiently cold enough. The rear air stream was operating at design capacity, and blower speed did not affect the overall temperature of the discharged air. As a result of testing it was found that the temperature door within the front HVAC module was exhibiting a “float” condition, where full cold operation was not being achieved.

Drive Complete: When a singular drive (damper actuator) completes, there is a check sequence built into the logic of the control head that looks for any overshoot from the target destination. If there is an overshoot condition, the software will update the current position as the original target position, therefore avoiding and “hunting” by the damper.

These two logic paths (executed within the control head software) operate at different rates. The target update task is executed and checked at a rate of 20ms, while the drive complete task occurs every 100ms.

Root Cause: “Any time the temp knob is turned, there is a chance that an intermediate value can be read and acted on.”
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have the same problem?
Wednesday, February 13th, 2008 AT 2:52 PM

1 Reply

I'm also having a problem with my front heater. The heater seems to be cycling in the outside air when the revs go below 2000rpm. If I'm parked, and rev the engine, I can hear the flap close and I get warm air again. This has become an issue since the outside temp yesterday was -35. By the way, the chevy uplander is an excellent cold starter.

The manual says that the outside air shouldn't cycle if the temp is below +32.

So, can you tell if your uplander is cycling air from the outside or inside?
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Friday, February 22nd, 2008 AT 9:25 AM

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