Bigpapaolds

My 66 olds 98 defroster will not work. Any suggestions? The car has A/C.

Oldsmaniac

Need info...fan runs?....fan runs but no air out of defrost vents?......if so a vacuum operated door opens and is controlled by push button controller for heat ac etc. Try tracing vacuum lines under dash to see if they are connected or leaking. If fan does not run thats where to start.

Bigpapaolds

Fans runs and vacuum lines inside the car seem fine. I'm not so sure about the lines under the hood. I took a line off at the switch and it hissed so I am getting vacuum inside the car. I can make the floor vents work by reaching inside the vent near the dashpot and pulling the lever that moves the air to the floor but I have not found anything to push or pull to force air out at the top of the dash.

Oldsmaniac

As metioned, the controller send vacuum to different actuators to send air topside for defrost or down to the floor for heat or thru the dash outlets for AC. On top of the heater box will be 2 outlets for the defrost air. Make sure the two air hoses are hooked up and not torn. You may want to pull the heater box out to bench test all of the actuators and to be sure there are no blockages due to mice nesting. At the least, you may have to remove if not already done so, the plastic AC ducting from under the dash to troubleshoot. The controller could still be at fault but from my experience it usually is a vacuum problem or actuator problem or disconnected air hoses to ducts.

Bigpapaolds

Thanks, it looks like the box is going to have to come out. I do have one empty fuse spot (my dash lights have been out) and I'm going to fill it and see if that helps.

Bigpapaolds

If I manually work the doors, I can get air pushing out the defrost vents. If my flaps (doors) are not closing when they should is that a problem with the dashpots or a problem with the switch?

bigoldscruiser

I'm assuming that you are talking manual A/C here. I sounds like a vacuum control problem. There is a circular vacuum switch on the side of the control panel with 5 hose connections which is controlled by a bar moved by the push buttons. Try each position and check the hoses for vacuum. One hose has a tee connection with the branch going to a second vacuum switch mounted on the back of the control panel. If all positions have vacuum, the door actuator must be bad or the door is binding for some reason.

Bigpapaolds

I meant manually as in I reach my hand through and hold the door near one actuator closed and then with the other hand pull the lever on the other actuator to close it. Then I have air going to the defrost vents. How do you check the things you were talking about to see if they have vacuum?