"AC OFF" Temperature gauge stops registering temperature.

Dear freemba,

Thanks alot for your reply. Will check the coolant asap and report back, haven't had any cooling system work done though. Removed the battery and reconnected after 20 minutes, did not solved the issue. Then I did what you said and bam! The car is fixed and I am back on the road. Thanks I love this site.

Best Regards,
Shehryar

A/c off and engine temperature gauge is a problem I have on my h3 hummer 2008 as well. I changed my coolant temperature sensor too but that didn't work. I accidentally found out that when I play with the hvac knob the a.C light
Engine temp. Gauge acts crazy causing my a.C to turn off. I realized that I recently left the control knob that controls the air duct flow (front outlet, window air duct, floor air flow) off and my a.C hasn't stopped working since. I am convinced thru process of elimination that the problem lies within the hvac assembly somewhere perhaps the resistor. The problem started after I took my hummer in to gm dealership for blower motor harness recall replacement. Play with your air flow direction knob by leaving the knob in off position and see if you a/c light and engine temperature gauge does not interrupt your a/c. Hope this helps !

Every now and then the temperature gauge drops to zero and "ac off" warning appears on screen and ac stops working. This has been going on since two months. Everything else seems to be normal, just the car has started driving a bit sluggishly but it unnoticeable and may be related with the oil change which is due also the steering may have become a little bit heavier.

I had the exact same issue ("ac off light" engine temp. Gauge inoperable. I had the thermostat replaced and my issue was solved. (It is a defective gm thermostat) that should be recalled. The computer is confused so it shuts down the ac to help prevent overheating; but also causes the engine temp. Gauge to become inoperable. For questions respond to this post.