My heater in my 98' Jimmy won't turn off. It stays on low the entire time the vehicle is running. I have tried all of the settings and it doesn't help. When you turn on the A/C, you can hear the compressor kick in but it still blows hot air. You can adjust the settings (floor, panel, defrost) and all of that works fine, it just stays on the hottest setting...HELP!

Are there any warning lights illuminated on the dash, (service engine soon etc)?

There are no warning lights on.

The automatic HVAC system should not allow the compressor to run when ambient temperature is below 38F. The system employs 3 temperature sensors, 2 control modules, various switches and motors, and electrical circuits that interact with the body computer. Unfortunately, due to the complexity of the system, proper diagnosis requires the use of a tech II scan tool. You can try disconnecting the negative battery cable for 30 seconds and then check the fuses. If that doesn't fix the problem, any shop with a tech II scan tool and a competent electrical technician should be able to find the problem.

Thanks, I will try to disconnect the cable tomorrow and I have already checked the fuses and the wiring to the module and relays.

Try spinning the dial a few times and clean the contacts off and then run in a full cold position (no auto on any dial) - if not you have a diverter door that flips for hot/cold vac controlled and also an electric door for the auto selection which has a plastic gear. Then the scan tool and I would highly recommend a GM dealer cause small shops do not see the auto climate system often and usually cost more due to time involved.

Thanks, I know the door for the positions in "auto" mode works fine, but of course the "auto" temp mode runs the fan on high unless you have it in the full heat position. I plan on taking the control unit out this weekend and inspecting the contacts/vac lines for corrosion or damage. I want to try to do as much as I can before I pay the GM dealer.

Please post back with your findings. Thanks.

I will post my findings...it will be a couple of days...I'm trying to kick this cold I've got first...ugh....