My 1986 F150 suffered the dreaded condition of no air direction control with air just coming out the vents, regardless of where the A/C heat selector was set. This has been written about before, but just having spent Saturday tearing into the dash, I thought I might be able to answer some questions regarding accessing the broken door.

I went to the Technical Tips section and thanks to the GREAT diagrams and pictures, was able to undertake this job. Thanks guys!

 

Check for vacuum before tearing into everything. There's a round thing with couple of small hoses running to it under the hood on the passenger fender liner. That's your vacuum reservior for the HVAC system. Make sure there's vacuum there. Then check the back of the HVAC control box. There's what is essentially a small vacuum manifold on the back of the control box that directs that actions of the blend door. Then check for for vacuum at the diaphram on top of the blend door. If all that checks out, the next thing to look at is the action of the diaphram and blend door. If the blend door is the issue, then you need to really start the teardown. BTW, taking the dash cover off will greatly anhance the ability to get at some of the underdash stuff.

 

I checked the diaphrams and they are both working properly when I move my selector while the truck is running. The vents have been stuck in the 'VENT' position. I got to the diaphrams after pulling apart the dash almost completely.

The door was moving but was not snapping closed. There must have been a spring to assist snapping the door closed all the way because there is a provision next to the pivot pin for this door that attaches to the diaphram arm.

I found a weak throttle return spring about 2 inches long a attached it to the door near the pin and then onto the dash/vent housing.

It works right now!

I will put it back together soon and advise how it goes....