I have an 89 F150, 351 AT with A/C. I just had a small fire in the engine compartment on the passenger side by the firewall. Some vaccum lines such as the PVC line burned, and I've replaced them all. My only problem is that now the heat/AC selector lever doesn't seem to do anything. All air is directed to the defrosters, the panel and floor settings don't work. The temperature lever (cold -> hot) seems to work ok. Is the selector level vaccum controlled, and if so any ideas where I should start to look?

thanks in advance,
Mike

 

Yes. It is completely vacuum controlled so you've missed a vacuum line somewhere.

 

As a result of the fire, the plastic evaporator box had a hole burned in it. Does that have to be completely sealed in order for the heater/ac vaccum equipment to work properly?

 

No. I don't see how that would make a difference. Furthermore, I recently had the resistor pack out of the plastic part of the box and it was not sealed in any way.

You might start by tracing it back from the control panel. There are color coded vacuum lines at the back of it on the right side of the control panel. I don't know which one is the supply but I'd definitely start there and see if you have supply vacuum. If you don't then the easy fix would be to run a new supply line to that point.