Manual HVAC control repair?

[Dud1f3r]

Has anyone taken their HVAC controls off and looked to see what broke in them? I'm thinking maybe it's the dials, or possibly a capacitor like old computers (or the OG XBox). Not really wanting to spend upwards of $120 on a control panel for a truck I paid $450 for. I have a 97 K1500 in case that matters.

Worse comes the worse, anyone know how it controls the blend door, fan speed, and mode door? Could possibly get a cheap lil Arduino to read inputs and tell it to output a specified demand based on interior temp and driver request.

 

[AK49BWL]

Fan speed is directly controlled by the switch. Common issue is the connector to the back of that switch burns up due to the high current draw. 88-94 used relays to control fan speed and personally I think they should have kept it that way. All of them use a little resistor module for voltage drop to the motor based on the selected speed at the switch.

Another common problem is one or more of the transistors burn up. Capacitors are actually not usually the issue on these.

All three door actuators are activated by 0-12v depending on where the knob is pointing. Electronics internal to the actuator control the position based on the input voltage of the third pin. If you go the Arduino route, you might be able to get away with using a PWM output to it, but definitely verify that because I've never tried it myself lol. A/C is a positive input to the PCM, easy enough.

 

[Dud1f3r]

A/C is a positive input to the PCM

Does this mean all the button does is say "Hey, I'm requesting AC" and the PCM determines if the AC should be commanded on?

 

[AK49BWL]

Correct. 96+ the PCM monitors the high and low pressure switches as well.

 

[1998_K1500_Sub]

Much, if not all, of the HVAC system's function and control is in the factory service manuals, they can be found here in .pdf form:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

The actuators can act up, and the doors inside the air handler can benefit from replacement, and the control head can have its issues, YMMV.

I've never had an actuator fail, my control head works fine, and I haven't had the clear need to rebuild my air handler, but others haven't been so lucky.

There are many threads that cover the air handler and actuators in detail. You might peruse this thread and take note of those who respond knowledgeably, and then search their posts in other threads or contact them directly.

HVAC box removal

I need to replace the doors in my HVAC box. I know you are supposed to remove the dash before you remove the HVAC box. My problem is my dash is cracked badly and I cannot find a good replacement in my area. If afraid that when I start moving it around it will be in several pieces by the time...

www.gmt400.com