HVAC Problems

jdnoble18 · April 27, 2016

I am having horrible trouble with the HVAC.

90% of the time it runs cold on drivers side, hot on passengers side - on defrost - not adjustable no matter what setting is on the CCM
5% of the time the temp works on the drivers side but still is stuck on defrost
5% (if that) of the time it works as it should

You can turn off the CCM and turn it back on and feel the blend door reach the dash vents, then it seems like it cant hold that position and defaults to defrost.

I bought a temp actuator and put it in (on the drivers side position, under the dash) but nothing changed.
I bought a blend door actuator but looks harder to change than I feel comfortable with.

I've tried resetting the system several different ways (negative battery cable, pulling fuses, unplugging the CCM) then letting the system re-calibrate for 30 minutes before I start the vehicle. Nothing works.

All these things happened at one time, the problems did not accumulate over time.

I've read that a dealer might provide an update but I really don't want to go the dealer route unless I have to.

To me, it seems like all signs point to the CCM or (BCM Programming) being bad, since all problems started at the same time.

If one actuator does not work, does all the actuators go to their default?

Has anyone else had trouble like this before?

Any help is greatly appreciated, thanks!

jdnoble18 · April 28, 2016

Thanks for the reply!

I took mine apart a few nights ago to see if I could notice anything out of the ordinary (thinking bad caps or something similar) but both boards inside the CCM looked normal.

I've got a new one in transit from someone on ebay.

I will check back and let you know if this fixes it.

sahls01gmc · April 27, 2016

I would look into your CCM, seems like all signs are pointing that direction.

jdnoble18 · May 2, 2016

SOLVED!

I ordered a new CCM from ebay and put it in. Same problem. I had replaced the drivers side temp actuator before with no change, so the next easiest to change was the blend door.

I ordered one of those, took everything apart. Go to put the gear back in and before I attach the actuator to the gear I move the gear by hand to make sure everything is positioned right....and the gear is stuck! I apply a LITTLE more force and feel something in the works give and I hear a woosh sound come from the box and a click from the gear and BAM! the whole range of motion is smooth. I put the actuator back on and put the dash back together, do a master reset of the truck by hooking positive and negative cables together for a few minutes. Hook the cables back up later, let the system relearn and I watched the blend door move the full range of motion just to make sure nothing inside the box is broke. EVERYTHING WORKS!

I'm not sure why things got off track, nothing was broke (even inside the actuator itself).

But anyway to add to what I've never read on the GMT900 platform...if your blend door actuator doesn't calibrate successfully, your system will default to 100% cold on drivers side, 100% hot on passengers side, and mode will default to defrost. Therefore giving you no clue to what actuator is actually broke, cause none of them work right when one is broke...they all go to default. The only way you could have seen this is on a tech2 I suppose.