no defrost
Senior User
Joined: Mar 2003
Posts: 302
Likes: 0
From: Cincinnati, Ohio
no defrost
I believe your defrost, heat and ac ducts are controlled by a vaccum motor under your dash. Look under the hood near the ac box. You should see some vaccum lines. Trace them out. And make sure your getting good vaccum.
zanny
zanny
Senior User
Joined: Dec 2002
Posts: 149
Likes: 0
From: Huntsville USA
no defrost
I have the same problem. If your vacuum motor is working, it could be the door it is attached to. That's what my problem was on my 84.
Just as a quick test of the motor, you can pull the radio bezel out of the dash and move the control arm back and forth. You should be able to find an angle where you can actually see if the motor is moving or not.
If you pull the cover off the heater core on the inside, stick your head up under the dash and look at the duct coming off the heater core. There should be a door there.
When you switch to heat or defrost, the vacuum motor pushes an arm that is attached to that door, and moves the door to close off the air conditioner vents.
When you switch to AC, it pulls on the door and closes off the heat/defrost vents.
It is held on by a film hinge. My film hinge broke, causing the door to be stuck on the A/C vents.
I found that if I reached up in there, and moved the door to block the A/C vents, I had heat and defrost. This worked fine until I moved the control over to the AC side. Since it was pulling, it moved the door into proper position. However, if I tried to go back to heat/defrost, the door would just flop around, and would not go into position.
I still haven't fixed it yet. I hope to figure something out before winter.
Rick
Just as a quick test of the motor, you can pull the radio bezel out of the dash and move the control arm back and forth. You should be able to find an angle where you can actually see if the motor is moving or not.
If you pull the cover off the heater core on the inside, stick your head up under the dash and look at the duct coming off the heater core. There should be a door there.
When you switch to heat or defrost, the vacuum motor pushes an arm that is attached to that door, and moves the door to close off the air conditioner vents.
When you switch to AC, it pulls on the door and closes off the heat/defrost vents.
It is held on by a film hinge. My film hinge broke, causing the door to be stuck on the A/C vents.
I found that if I reached up in there, and moved the door to block the A/C vents, I had heat and defrost. This worked fine until I moved the control over to the AC side. Since it was pulling, it moved the door into proper position. However, if I tried to go back to heat/defrost, the door would just flop around, and would not go into position.
I still haven't fixed it yet. I hope to figure something out before winter.
Rick
