Heater controls

[slipbobbin]

I have a 1989 Suburban and cannot get the heater controls to switch up to the defrost. I took it apart and it seems like everything is hooked up. Blows hot air on the floor board and through the vents but not out the dash. Any ideas on what could be the problem?

[Jeremy airjer W]

When youhadthecontrolheadoutdidyounotiveifthe control wasa vacuum control electronic control.

I think this is old enough that its a vacuum control. The fact that it is switching from floor to vent is a good sign. It means there is a vacuum supply and the mode selector is try to work. The next step is to find the vacuum actuator that controls the defrost mode door and check to see if there is vacuum present with the switch in defrost. You can also check to see if the actuator moves freely or binds.

[slipbobbin]

Everything seems to be moving freely. Didnt even think that is could be vaccum. Will check that out. Thanx

[Jim Almquist]

My old 89 Sub. had the same problem. If you drop the glove box and reach in there you will be able to move the arm and get defrost. If you switch to floor it will not come back. I ended up tying a string on to the arm and just pulling it when I wanted defrost. Let the string sit in the glove box.

[Jeremy airjer W]

Wow, my post made no sense! Stupid Ipad!!!

it should read,

When you had the control head out did you notice if the control was a vacuum control or an electronic control?

"I think this is old enough that its a vacuum control. The fact that it is switching from floor to vent is a good sign. It means there is a vacuum supply and the mode selector is try to work. The next step is to find the vacuum actuator that controls the defrost mode door and check to see if there is vacuum present with the switch in defrost. You can also check to see if the actuator moves freely or binds."

I think if there is no vacuum it should be in the defrost mode and if there is vacuum it will be in another mode

You can also try this. Remove the vacuum supply from the control head. The mode should default to defrost since the default mode with no vacuum is defrost.

[Capt. H (Ret.)]

Airjer,

When I read your 1st post I thought "WOW LOOK AT HIM GO THE BRAIN IS WORKING FASTER THAN THE FINGERS"!!!!!!

I read your posts all of the time because I think you give good information.

Mike

[Jeremy airjer W]

LOL!