Starting a new thread, because I haven't seen a current one (less than 5 years), and I know the rules around here.

My 2009 H3 standard (141000mi) now has this problem. AC blows full Cold -- if the temp **** is moved even 1 click towards warm, it blows full hot). It did not have the problem when I bought it earlier this year.

My problem started after I replaced the starting battery.

Some info from my experience, and soliciting any suggestions.

I also had the same problem with a previously owned 2005 GMC Yukon Denali.

​​​​First, there are 2 separate AC reset procedures. There is the one that happens when you disconnect/reconnect the battery. It is important to turn the ignition switch on, and then not touch anything (don't start the vehicle, don't touch ac controls) until the sequence completes. Once complete, and while still not touching any controls, turn the ignition off, then operate as normal) I'm not sure what positions the AC controls need to be in.

This is what I think may have started my problem. The battery replacement was essentially a road side repair, and I was anxious to get moving again, so the sequence didn't complete.

Repeating this battery disconnect would fix the problem on the Yulon about half the time. It would cause it the other half of the time. (like any time I had to disconnect the battery.)

The second reset procedure is setting the ***** to Full Heat, Full Fan, top vents (Right, Right, Left) and then press and hold both the AC button and the Rear Defrost button until the LEDs start blinking. (Again, ignition switch on, engine not running). Allow the sequence to fully complete. When you are sure it's fully complete, wait longer, because it does stuff with the actuators even after an additional delay. The turn the ignition switch off, then operate as normal.

Note also that I have been playing around behind the dash/AC panel because my H3 has an aftermarket head unit, and I was in there cleaning up some wiring.

I've tried the "in cockpit" reset several times, but still have no temp control. I tried disconnecting the battery and allowing the startup procedure to complete, but that did not fix the problem.

I guess I am asking for the recommended next step -- The resistor trick (as described elsewhere) -- Actually trouble shoot the AC control board, or try the battery initial calibration again after leaving it disconnected for a longer time?

Has anyone fixed the problem by cleaning the contacts on the AC control module?

Has anyone troubleshot this issue down to an actual component on the AC control board?

Is there a way to get the AC to blink out a code? There is no code when I do a diagnostic with a code reader that can supposedly detect the AC module. Is the AC module even that "smart" on the H3?

 

Definitely give the resistor trick a try; it is relatively painless to do, and generally speaking, fixes the symptoms you described (but not always).

There are plenty of topics/info out there on older posts regarding how to do it. 68 ohms is ideally what you want; I’ve heard (but not verified) that 100 ohms will also work if that’s all you have laying around in your garage.

I got my 68 ohm resistor from Amazon

 

GM fixed this with a redesign of the board, but the after market solution is to add a resistor in line to ensure the 5V AC reference signal stays in bounds. I had this problem on my last H3 and this was the permanent fix for the problem.

Here is Hunner's original post on H4O: https://hummer4x4offroad.com/forum/t...trol-fix.3962/

Or you can find that reposted on this forum here: https://www.hummerforums.com/forum/h...p-28289/page4/

 

Thanks, All.

I'm also an electronics Geek, so I have lots of resistors of various values/wattages laying around, Don't expect a reply quickly, as this is not a high priority, but I'll post back with results.

 

I did the resistor trick one month ago based off the advice on this forum. Took 30 minutes max with the $2 resistor from ebay and my poor soldering skills. Has held up just fine and has full range from cold to hot.