I need a little help deceding on where to look for this problem. The problem Is when I turn on the Floor vents very liitle air comes out of the floor and most comes from the main vents. The same thing also happens when I turn on the defrost. I am thinking it is a possible vacuum problem. It might not be able to move the door back and forth. Trouble is I don't even know how to start diagosing a vacum problem. Please help.

1986 F150 Lariat
5.0fi

 

check under the hood near the heater coil. There should be a vacuum line on top of the cover. If this is missing or broken then the vents will not move.

 

Sounds like a control unit gone bad...common problem

 

Control Unit?

 

isnt that the little silver round thingie behind the radio

 

you mean below the radio? By the way how do I test it to confirm that it is the problem?

 

I can't find a pic of it but yes the area near the radio that you change the AC/heater settings.
That unit is what goes bad and doesn't allow doors to open and close diverting air.

 

I followed the steps that "Paden" gave me below and this was exactly my issue. The flapper door was broken at the cheap plastic hinge. follow his instructions below and you should have no problems. It took me about a half of a day to repair this and only cost me for the hinge i got at home depot. Trust me I am no mechanic either.

I assume it has A/C since you mentioned vents. Usually when the door breaks on an a/c system you get what you describe, air through the vents and not much through the floor or defrost vents. If you don't use or don't need the a/c you can just tape over the door or block it off somehow, the floor and defrost will work properly.

Ok, to try to explain how to get to it without completely dismanteling the dash....

First remove the dash cover and the middle (radio) trim piece. There is a plastic vent tube across the top that needs to be removed, it is jointed behind the radio or slightly left of it, this means the metal pieces directly above the radio need to be bent up and a the center speaker removed if it exists so get that metal speaker holder piece bent up. You need to remove the glove box door and liner next, that is fairly straight foreward. Now remove the 2 bolts mounting the right side of the dash assembly, the lower bolt is on the right wall in front of the door if I remember correctly and the top one can be removed from the top close to the window corner, they are 2 different sizes so you will need two different wrenches :-) Once those are out you can gently pull the right side of the dash assembily out and with a little struggle you should be able to remove the plastic vent pipe. Once it is out of the way you will see the hole where the vent door belongs, it will probably be laying sideways inside there, don't just rip it out, you need to remove a plastic pin that holds the vacuum actuator rod to the door, then you need to drill out the plastic rivets that hold the rest of the door hinge to the heater box (check first and make sure the hinge is actually broken :-).

You need some patience to put the new door in, it can be tough to get the pin in and then figure out how to get the rivets in but I assure you it can be done, I have done three in the past. Like I mentioned earlier if you don't want a/c or need the defroster in an amergency etc, just tape over the hole where the door should be, you don't even need to put the vent duct back in.

Hope this helps.

 

I had the same problem and the above fix was right on target. Not hard to do, just a little time consuming.

 

Thanks I will give that a try

 

Just FYI, you don't have to bend the radio speaker metal piece. With the dash pad removed, you can unscrew it. The only hidden screw (sort of) is just to the left of the speaker near whe windshield. There's three in front (couting that one) and the two above the radio ). Just saves a litte bent metal and it'll make getting out that vent tube easier.
Have fun!

 

Just wanted to say that I followed these instructions and good-enough-for-me-fixed the defrost and floor today. What I mean by that is I covered over the vent hole so that it only comes out the defrost and floor now. I needed those (especially defrost) way more than I needed the vent, and besides, as far as straight heat goes, that heater unit works so well in my '86 that I really don't need anything blowing right on me anyway.
Ogre