Heater Control Cable Hook Up for 79 C-30

[brandon]

Good Morning all. My heater control was broken when i bought my truck and the ex father-in- law unhooked it, but didn't mark the cables. I recently got a new heater control and I'm not sure what cable hooks up to what arm. I found the two behind the glove box, and i'm sure one of them controls heat/defrost and marked it. I can't see where the 3rd/other cable goes too. I have 3 cables and 3 arms to connect them to. There are 2 connections for the OFF/HTR/DEF and one for hot/cold. Please help or point me in the right direction. I can supply pics if need be. It's a '79 C-30.

[Captkaos]

Did you look at the Service manuals on the site in the Tech section?

[bd]

The three cables are: (1) air cable, (2) defrost cable, and (3) temp cable.  View Figure 1A-14 at the bottom of page 1A-12 (pg 37) of the 1979 Service Manual.

[brandon]

Thanks for the diagrams, I had no idea they could be looked at. Now, i can locate the lever to the air cable. Can you tell me the function of the Air Cable? My truck has separate controls for the Heat and AC. There is also no AC under the hood. I'm almost certain the Temp and Defrost cable are the ones behind the glove box. Since the Heat and A/C are separate, do i need to hook up the air cable?

[bd]

Study Figure 1A-1 on page 1A-2 (pg 27) of the repair manual.  The Defrost cable attaches above the center hump.  I believe the Temp cable attaches to the lever arm that is left and closest to the dash behind the glove compartment, the Air cable attaches to the lever that is right and behind (a smidgen closer to the firewall).  The Air Valve opens and closes outside air entry into the cab, Temp regulates the volume of air passing through the heater core versus bypassing the core, Defrost opens and closes the defrost valve directing air to the windshield.

Your A/C is not factory GM.  That is why the controls are separate and you have three cables controlling heater/defrost/temperature functions.