A/C & HEAT slider is froze up

[74chevyc30]

74' c30:
A/C and Heat slider on my control unit in the dash will slide all the way to A/C but when moving back to heat it freezes up half way.

Is there a cable that hooks to this slider behind the dash? If so then maybe the cable is froze up? That would be easy to figure out if I unhooked the slider from the cable and the slider started working fine. But I have no idea if there even is a cable hooked to the slider mechanism. Or if the slider is just and electronic switch or a vacuum switch.

I'm just spit balling here. Please let me know how the A/C and Heat slider mechanism works on the control unit. And maybe some tricks I can use to free it up. Thanks guys.

I will post a pic of the style of control unit I have.

 

[75gmck25]

There is no cable connected to the upper slider, but there is a heat blend door cable on the bottom slider. When you move the upper slider it is connected to a large plastic assembly on the back of the controls, and all the HVAC vacuum lines connect to the plastic assembly.

If that plastic assembly on the back of the controls is broken you will be searching junkyards or eBay for a replacement, because I do not know of any supplier for a new one. However, if it’s the metal slider and control assembly that is broken you can get a new one from LMC truck or other suppliers.

 

[hey mister]

I'm not certain how that year is set up.
My 78 is stiff cables in a sheath. So I suspect yours may be similiar.
Mine too was behaving in the manner you describe.
They are not difficult to work on. Maybe a bit fiddley.
But the cause of your issue may be a gummed up air/heater box.
If it has never been taken out and refitted with new foam, the old foam is deteriorated and may be jamming up damper doors.
Just get a flashlight and get under the dash. You will see the 2 cables attached to the slider panel. Follow them over to the airbox.
Each cable will go to a damper door arm on top of the airbox. Gently try to move the arm. Your slider should move as well. You may be able to determine where the jam-up is occuring.
It may be the slider mechanism is damaged (mine was from someone trying to force it) or the airbox. But it may also be the little clamp at the end of the cable. Make sure the sheath is not slipping under/thru the clamp.
Either way replacement components are available.
I replaced my heater core, slider, cables and rebuilt my airbox with new foam.
You can find my thread on it, in here somewhere.
It was a bit time consuming and a bit fiddley, but I enjoyed the project and learned alot.
It was not at all difficult.

 

[edgephoto]

I am restoring my 1987 V3500. I had the HVAC controls out and all apart to clean and lube them. Not a very hard job. Could just be full of crud.

 

[74chevyc30]

Where can I find replacement foam for the box and dash air vents?
Also where can I find the slider parts or cables?

 

[jetdexter]

Sorry I don't have an answer for you, but I was wondering the same thing. I'm ordering a set of new vents (mostly because many of the fins are loose and floppy) But I realize that the surround foam is what holds the vent into position, so that would also need to be replaced.