I inherited my grandfather's 86 F150 this year. One thing I have noticed since it has gotten cold is no matter what position I put the function lever (the one choosing a/c, max a/c, vent, defrost, floor, and combo) the air only comes out of the vents on the dash. The defrost, floor, and combo setting do not work. This is not very good when there is frost on the windshield because I have to wait for the entire cab to get at the proper temp before it will go away and forget about it if it starts to fog up.

This weekend I looked underneath and behind the control assembly and saw that the cable was not attached at the back of that lever. The temp. control cable was attached though. I thought to myself no big deal, just find the end of that cable and reattach it. The problem is I can't locate the function cable and I'm not sure exactly where it attaches on the other end to follow it back. I can follow the temp cable with no problem but either the function cable is gone in my truck or there are too many wires in the way for me to see it. Can anyone point me to a manual that can help me, beside the Haynes manual as it doesn't have a very good section on this, or tell me where to look. I'm trying to keep from removing the entire dash but I'm afraid I may have to in order to see exactly where everything is. Thanks for any help you can give me.

 

I found out the other day on here, that you can take the top of the dash off very easily on these trucks. A couple of screws over the cluster, and few along near the windshield, and a few more(can't remember exactly) and the top comes off for easy access.

 

Those functions are controlled/operated by vacuum. There should be a vacuum manifold on the passenger side firewall (underhood) with a line going through the firewall to the selector mechanism in the dash mounted control unit. Look for bad hose/tubing. Also, could be the control unit itself.

 

I'll check that out. The Haynes manual doesn't cover this very well. I think the control unit is ok though or atleast working partially as when I move it to A/C it kicks my compressor on. Thanks for the help.

 

There is an electrical switch on it that turns the compressor on in A/C and Defrost. The vacuum switch controls the vacuum solenoids that operate the function "doors". The temperature cable controls the "blend" door. Pencils, keys, loose change, etc. often finds its way down the defroster ducts and interferes with the operation of the doors.