AC/Heater control switch issue
 

I only have air coming out at the defroster. I can move the switch from position to position and the air flow doesn't change. When I move the switch from the different settings, it make a positive stop at the floor position. The others it seems to glide on past.

Is this an issue with the switch? Is it something that is replaceable instead of replacing the entire control panel?

Thanks for your help!
Steve

Re: AC/Heater control switch issue
 

Year?
AC or No?

Re: AC/Heater control switch issue
 

97 with ac

Re: AC/Heater control switch issue
 

It's probably the motor that controls the vent selection. It's above the gas pedal and is pretty easy to replace. Check the linkage up in there too, it might be loose.

Re: AC/Heater control switch issue
 

Is this what you're referring to?

http://67-72chevytrucks.com/gallery/...door_motor.jpg

Re: AC/Heater control switch issue
 

So I removed this motor and left it plugged in while changing the switch. There was no movement when I changed the switch positions. I can manually move the blend door from position to position easily.

So is this motor or the dash switch more likely to fail?

Thanks again for the help guys!

Re: AC/Heater control switch issue
 

I've had theMode Door motor and a blown transistor on the dash controller do this. If the motor isn't turning it could be either...
Usually the motor isn't the issue with actuator failure... it's stripped internal gears. Been there done that on several GM vehicles.
If you dig around in the 98 service manuals there's likely a test procedure.

The Mode Door motor is less expensive to replace but it's still $20-$30. But I'd lean toward the dash switch module. The last one I replaced was $100 or a little more from GM.

The Mode Actuator or Motor controls the air flow door or flap... Floor thru Defrost. The Mode Actuator is on the driver side of the HVAC box near the accelerator pedal.
The Blend Actuator or Motor controls the temperature door/flap.
The Recirculation Actuator or Motor controls the Recirc or Fresh Air door/flap that routes air from outside or inside the cab to the HVAC box.

I believe Blend and Mode motors are the same part on the GMT400 after 95 or 96.

Re: AC/Heater control switch issue
 

The little bit of testing I did was looking for voltage at each of the 3 wires when changing the mode. I only had power one the black wires as I changed modes. I also heard nothing when I removed this one near the gas pedal and went thru the modes.

Re: AC/Heater control switch issue
 

Sounding more and more like the switch.

Re: AC/Heater control switch issue
 

That’s what I think also. Is that something that can be replaced by itself Instead of the whole control panel?

Re: AC/Heater control switch issue
 

The problem switch on the left is attached to the board with the middle switch and the two push buttons. It doesnt look very serviceable.

http://67-72chevytrucks.com/gallery/...MG_6878_1_.JPG

Re: AC/Heater control switch issue
 

Difficult at best.

Usually it's not the rotary switch itself. The control circuit causes issues. It's all one part and I never took the time to troubleshoot what actually failed on the boards.

There are one or two T92 package transistors and at least one electrolytic capacitor IIRC.

Re: AC/Heater control switch issue
 

I appreciate the help with this issue. I will check some local salvage yards for a replacement control panel and see if my issue changes. New part are $140+.

Re: AC/Heater control switch issue
 

Re: AC/Heater control switch issue
 

Thanks Speedy, but my issue is with the mode switch. My blower speed switch works fine at all speeds. Im having issues with changing the wind direction.

Re: AC/Heater control switch issue
 

They can probably be repaired if you have the tools and experience...
My bench toys... You don't want to see the workbench right now.

Attachment 1839688
Attachment 1839689

Re: AC/Heater control switch issue
 

What is your shipping address again? LOL! You look like the right man for the job! :)

Re: AC/Heater control switch issue
 

I only do repairs for Myself, close family and, for my employer.
My hourly rate would make a new controller look real affordable.

I don't have an accessible test bed for that controller right now either.

Re: AC/Heater control switch issue
 

So one wire provides power to the motor, another is the ground, and the other wire is the reference wire that is told by the switch where to go, aka the position wire. The position wire does not get 12v, but I'm not sure what voltage it's supposed to be.

I'm not saying the switch isn't bad, but before you drop whatever at the junkyard or a new one at $140, make sure you test out that wire thoroughly. The factory service manual will have the correct info (available at a library) or see if ChevyTech chimes in with his vast knowledge and collection of diagrams.

Or get another motor and see if it works.

Re: AC/Heater control switch issue
 

The 1998 GM Service Manuals are in my Signature...

Re: AC/Heater control switch issue
 

Good call. Didn't catch it. Thanks for posting those BTW, they are very handy to have around.

Re: AC/Heater control switch issue
 

The motors are much cheaper.. I will also reference the manual. Thanks!

Re: AC/Heater control switch issue
 

Big time.
I'd troubleshoot it using the service manual if you can. Way cheaper than the shotgun method.

I won't be shocked to hear it's the controller. I've never seen a failed motor just stripped gears. Testing is free...

Re: AC/Heater control switch issue
 

sounds like a sticky actuator that controls vent doors.

some wd40 might free it.