S series tech for HVAC needed

[89GMCSuburban]

Battery went dead on my 99 Jimmy with auto HVAC. Now, after I got it jumped, the blend door cycled from cold to hot on the drive back home and then stuck to heat all the time. There's a noise coming from behind the dash, starts as a scraping, then turns into a squeeking, then pops and goes away for a few seconds before it's back. The modes work fine, and the noise is continuing now even though heat is stuck on full bore.

I've had no luck at ALL trying to find any kind of troubleshooting book, and as we all know, Haynes manuals are crap. So, short of my buying $125 worth of factory service manuals, anyone know where I can get some troubleshooting steps, or maybe you've run into this before?

 

[Jason4x4]

usually a bad blend door motor.

 

[sled_dog]

see if you can access the blend door motor/actuator. If you can do so, unclip it from the blend door and try to manually move it. See if the blend door is bound up, or the motor is taking a crap on you. I'd bet more so on the motor, but never overlook the obvious. Can't be more help, no real experience with HVAC on S-Series.

 

[89GMCSuburban]

Either of you guys know if there's a "calibration mode" you put these things in so it knows where to move the door? The Behr systems on semi trucks have you put the fan/blend/mode door knobs at certain spots and hold the A/C and Recirc button and it resets the doors.

The motor is in a hell of a spot, I'll try to plug away and check if the blend door is ok (not broke) and if the motor turns to the command. Motor would be a first place to start, and if it's not that, probably the controller, you think?

 

[sled_dog]

yes but the audible noises sound much much more like a motor or binding of the blend door. Damned if I know what module controls the Auto A/C on that thing. BCM?

 

[89GMCSuburban]

I believe on this it's the actual control head has everything in it. The Behr system on semis even have their own J1587 datalink to talk to other parts of the truck! I'll pull the head on this thing and see if it's got any of the tell-tale color wires for datalinks on it, if she doesn't, I'd be safe saying the controller (knob assembly) has all the stuff in it....it better, at least. The thing is over $200 new!

 

[5280k5]

The basic function of the actuator when it's powered up is to run to each end it's range and splits the difference as center and then using a feedback circuit decides where to put it based on the knobs selection. Sounds like possibly yours may have gone past the end of its range and now it doesn't know where it's "home" position is and may be trying to force the door, maybe. Unfortunately most of the actuators cannot be repositioned but you will probably want to verify the door in the hvac case is working properly with the actuator removed. Nothing worse than putting a new actuator in and finding out the door has a problem and sends the actuator out of range again. Send me a PM if you need some help, I work at a Chevy dealer and could get you some specific info if you need it.