gmc sonoma climate control panel?

[JBC]

first it was the AC clutch not engaging. now, in a heat index of 110 the last week (humid too), the service providing for the heat/vent/ac/defrost appears to remain only on "defrost/floor vent combination" and will not respond to any change in the knob position.

Any ideas? I think the assembly is exclusively electric and not vacuum, but thats a guess, If I have to replace the climjate control panel, so be it, but Im just looking for some solid Dx advice right now.

Thanks

 

[Maranatha]

ac module, run checks to verify.

 

[epiphaknee]

Unfortunately you have not shared with us the year, make and model of your vehicle. So I guess you have a Sonoma between 1994 and 2004?

Generally the AC mode control switch is vacuum operated. The defrost-heat "position" is the default position - no vacuum present to open and close the doors. Hence, you have a vacuum problem. Generally this is either the AC mode switch, or a pinched vacuum line or leaking vacuum hose elsewhere (e.g. a bad vacuum ball etc.). Sometimes a bad AC mode switch hisses and you can hear it hissing just driving down the highway. This is also true with a compromised vacuum hose/line. Stop, look and listen...

So the first step would be to pull off the AC Mode Control switch, disconnect it from behind and determine if vacuum pressure is making it to the switch. If not, then you must trace back to the vacuum ball for a vacuum leak or pinched hose along the way.

Now is a good time to determine if some recent repair may have compromised a vacuum line. New heater core? Compromised vacuum line near the firewall inside the engine compartment? Also from about 1998 to 2003, the vacuum lines fill up with transmission fluid from a solenoid on the transfer case which is also vacuum operated. Have a reddish fluid in your ashtray? If you do you owe me... This solenoid is only about $15.00 and EVERYONE should replace the OEM unit.

Go for it!!!!