I have an 86 f150 and the heater will only blow through the vents. I have done some searches and think it must be the flapper that switches the air from the vents to the floor and defrost. I checked the vacuum motors and I can see them opening and closing the flaps but the air flow does not change. I think I might have something that fell down the defrost vents and is keeping the flapper from closing. How can I get to the flappers and visually inspect them? If I need to remove the dash, how does that come off? Any help would be greatly appreciated.

 

I have an 84 F-150 i am having a simular problem the flapper that works the vent/defrost is located behind the glove box and a little to the left. The solenopd operates but the flapper will not switch from vent to defrost when the blower motor is operating. I can reach the flapper from a cover located behind the glove box that covers the heater core. reach in and i can move the flapper but it seems to hang up. To reach it it seems that you have to really disassemble the whole ventilation system. I think they installed this flapper and built the truck around it. I have messed with it every way imaginable but have not gotten it to work reliably. I have vacuum tested it and it will hold vacuum fine.
Sorry i cant be more help.

 

Thanks for the information. It at least gives me a place to start.

 

I figured out what the problem was. The flapper door has a hinge made of plastic. The plastic finally just broke at the pivot point. The only way I could get to the door was to cut out the front of the plastic box that is in front of the flapper door. I used a utility knife that I heated up with a lighter. I was able to access the flapper. I will buy a small metal hinge that I will use to re-attach the flapper to the plenum. I know that is a lame description. If you need me to try and explain better let me know. When I am done I will use some high quality tape, like the stuff they use to put in duct work. Not duct tape. It is a foil backed tape. I will just put the piece I cut out back over the hole and tape it to seal it up.

 

This is a big problem with Quality One I see. I have the same problem and the keeper that holds the door to the rod attached to the vac switch is broken, after several attempts to fix the problem I took a coat hanger and bent a circle in the end and used a small self tapping screw to attach it to the top firewall side of the door and bent a little handle on the other end an ran it out the floor vent, so I have to reach down and pull the handle and now my defrosters work as well as my feet are not cold anymore.