NO FRONT HEAT - ACTUATOR OK

[tlong]

I have a 2000 Yukon XL with (are you sitting down) 450,000 miles on it (ok, replaced engine at 385,000 and rebuilt tranny/newer transfer case not long after). It does not have dual zone hvac, has the control with 3 knobs (fan speed; temperature; flow direction). I have just lost the front heat though the rear heat works fine. It was working the other day and as I neared my destination, noticed that I was suddenly getting cold air. I have read many of the posts regarding this issue. I flushed the heater core, it was clear with very little debris coming out, flow good. One hose very hot, other hose hot. I also went ahead and replaced the temperature blend door actuator (the one above the transmission hump). Problem is that neither of these things solved the problem. Oh, and I didn't know there were cabin air filters -- I pulled those along with about a bushel of leaves and pine needs and insect carcasses.

 

I am at a loss. Since it happened suddenly, I immediately think electrical. Fuses are fine. Actuator is new (and yes I calibrated it -- numerous times!). I also pulled the actuator and moved the door manually while "heat" was on -- made no frickin difference!!! Still no heat. What else is there?? The control module with the three dials on it? Some mystery relay that is hidden in the dash? Please -- NEED HELP. Not ready to get rid of the beast yet and need my heat! ANYONE out there have any ideas?

[gmtech4]

did you know there are DTCs in the HVAC system ?

 

get it scanned and reply with the codes

[tlong]

No i didn't. I do most work myself at a friends retail automotive repair shop. Have used scanner for engine codes, but didn't know there were hvac codes. Am stopping there tomorrow, I'll put scanner on and see what comes up. Will post results. Thanks for quick reply!