Rear AC blows hot but front AC works fine?

[merc81]

I recently solved a problem in my 2001 van where the rear AC suddenly started blowing hot air even though the front unit worked just fine as always. The back sometimes would work, but after a bump or sharp turn would start throwing out hot air again.
I located a motorized damper lever on the side of the rear AC unit that had three wires connecting to the module via a plug. I unplugged the cable getting ready to remove the module and found the center pin from the circuit board of the module had come loose.
I went to the local pick-a-part junk yard and found half a dozen more vans like mine, but all of them had the same exact problem--the center pin and sometimes two pins had come loose from the module! The modules swing a damper door from the hot radiator to the cold on the rear hvac unit and cost about $150 from GM. I found some on ebay, but there are several units that look the same and are made for different locations in the car.
For example, the rear hvac has two modules, one on the rear side below the fan motor for the hot/cold damper and then a 2nd module near the front just beside the middle row seat belt recliner. That module flips the blower output from ceiling to floor and isn't the same cam design.

The modules have three wires, a 12v hot, a ground, and in the center a variable voltage that is set from the temperature knob of the rear hvac control. When set to higher voltage (about 8 volts) the module turns its cam arm over so the cold radiator gets all the air, when set to low voltage (about 0 to 2 volts) it moves the cam to move air through the hot radiator.

This is all in the manual, but not very clearly. Also I noticed in the junk yard that 99 models used a vacuum system instead of the electric modules.
Just fyi, these vans are getting old now and some of you may be seeing this problem on your own units.

[brcidd]

GM parts sells a repair kit for all GM connectors- sold through Packard as I recall, I bought one about 10 years ago- use it on any connector issues.

[merc81]

Yea, this is not a problem with the connector that you can fix. The issue is the pins that are part of the circuit board are falling off the board. The connector is just fine and if I had a replacement module on hand, that's all that would be needed. I thought it would be useful to mention this problem because as I said, when I visited the bone yard almost every van there had the same issue--the pins were all coming off the solder joint on the boards.

I fixed my van by using a dremel tool to cut the module open and re-solder the pin back to the circuit board. I should have done that straight away without wasting time at the pick-a-part, but lazyness rules sometimes.

[Cressidaadr]

Originally Posted by merc81

This is all in the manual, but not very clearly. Also I noticed in the junk yard that 99 models used a vacuum system instead of the electric modules.
Just fyi, these vans are getting old now and some of you may be seeing this problem on your own units.

If I am understanding I think you are suggesting that the early models (97-99) may not develop this problem because they did not use the electric modules - is that correct ?

[merc81]

That's right. Since the 99 models used a vacuum actuator instead of the electric module, they can't develop the same problem. I'm not saying they don't have other issues with the damper doors (none that I'm aware of), but the pin I'm talking about falling off the board can't be the cause because they don't have one!