SOURCE: I have a 2004 GMC
Remove the Positive Battery Terminal, leave the Negative Terminal connected. Wait 30 minutes. Attach the Positive Terminal. Verify temperature settings is around 70 degrees. This procedure has been known to resolve computer settings.
SOURCE: 2000 GMC Sierra 5.3 Litre, won't blow hot air
I experienced the same head ache. First attempt was to replace the thrmostat and after taking it apart I realized that there was nothing wrong with it. I then removed the plastic cover/panel located under the dash board on the passenger's side. (only a few 4-5 smalls screws) Removal will enable you to see the on/off switch/gate moving/rotating as you turn the knob to hot or cold positions, on the control panel. If that switch/gate seems to work ok, then the trouble is within the heater core. Many mechanincs suggested that I replace the heater core. A very expensive proposition.
I checked the heater core supply/intake hose and found it hot to the touch, while the return hose was nearly cold. It was definitely a heater core blockage. I removed both ends (supply and return) hose connections/clamps. They are located near the fire wall in the engine compartment. A special tool is very helpful to remove those clamps easily and to replace them as well. It can be done the old fashion way but this tool was a life saver and reduced work time to just minutes. (Tool is $70.00 bucks at auto parts store,so I borrowed mine from a mechanic/friend)
I then hooked up a garden hose to the return end of the heater core and reversed the flow of coolant/water through the heater core. My truck is a Sierra 2000 and I refuse to see how a heater core could get clogged up with clear coolant alone. To my surprise a flat piece of rubber about the size of a quarter blew out of it and the flow of water became unobstructed. I reconected the ends of the hoses to the heater core, replaced the lost antifreeze & everything returned back to normal. No money spent for something most mechanics suggested I replace control valves/switches ($280.00) replace heater core ($500.00) etc etc. I am glad I was curageous enough to tackle this myself and save a few pennies. Good luck, and I hope this will work for you.
SOURCE: removing the 2nd and 3rd row seats
3rd row, you simply pull the lever which makes the back fold down and then grip the handle located on the bottom and pull toward you slightly hard. They are heavy so it seems like they aren't coming out, just pull hard. second row, you flip all the way up and push with them standing up and they come unhooked. Good Luck! I didn't have any problems, except they are at least 50+lbs!
SOURCE: 2002 GMC Yukon front A/C blowing warm air
Here is a TSB (Technical Service Bulletin) for your vehicle for loss of temp control.
File In Section: 01 - HVAC
Bulletin No.: 01-01-39-007
TECHNICAL
Subject:
Loss Of HVAC System Mode and/or Temperature Control
(Reroute Wiring Harness)
Models
1999-2002 Chevrolet and GMC C/K Pickup Models (Silverado and Sierra) 1999-2002 Chevrolet and GMC C/K Utility Models (Avalanche, Suburban, Tahoe, Yukon, Yukon XL, Denali) 2001 GMC Sierra C3
2002 GMC Sierra Denali
2002 Cadillac Escalade, Escalade EXT
Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent.
Cause
There may be poor terminal contact and/or bent terminals in connectors C206 (RPO C68 automatic HVAC controls) or C296 (RPO C60 manual HVAC controls). Excessive tension on the wires due to the wiring harness being miss routed in the instrument panel carrier may cause these conditions.
If the warranty campaign is over i am sure they can or may have in the system on how to correct the problem.
Good luck and hope this helps, keep me posted if you need help on to the repair procedure.
SOURCE: 2004 GMC Yukon blows hot air out of the driver
Probably the left temp actuator. The wires in the right I/P junction block could have poor tension also, but it's usually the temp actuator.
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