Help Air only comes out the a/c vents

[alsohim]

I am stupid for getting rid of my books on these trucks! What controls the floor, a/c and Defroster vents? It wont switch is it a cable or vacuum or both.

TIA
Kaleb

PS 1970 Chevy C20 custom camper

[Woody]

There's a Deflector in the main airbox (under the left side of the glove box) that gets old and brittle then breaks. Move the "Heater-----A/C " knob side to side and look for the cable moving.

Order yourself a LMC Catolog...It has great detailed drawings of most of the trucks.

Woody

[Papa Smurf]

First, feel for the back of the A/C/Heater control and see if all of the levers move when you move the knobs. It is common for these levers to break. The system is controlled by cables and they bind up over time and can break the pot metal control arms.

Second, if the arms are not broken, it will be the big gray box under the glove box. The A/C/Heater cable operates a big flapper that changes from upper ducts to lower ducts(and defrost). This flapper is a plastic square(basically) with a rubber gasket molded around it. Also molded into the rubber is the shaft which connects to the cable, thus moving the flap back and forth. Over time the bottom edge of the flap will snap off so the rubber just flops back and forth instead of moving the flap to close one or the other air path.

Solution: Order a new plenum box(pretty costly)or fix the old one. I came up with a neat, cheap, permanent fix which I posted on here a couple of years ago. Go to "Air Regulator Question" 04-13-09 for detailed instructions and pictures. Believe me, it works great and you never need to worry about that part again.

Hope this helps. Stay cool/warm.

Papa Smurf