Defroster (and floor) not blowing air on my 1985 F150.

I manually moved the lever that goes into the aluminum cylinder on the passenger side close to the windshield and it didn't make any difference. All air comes out of the dash vents only.

Any suggestions?

 

likely a vacuum problem in the control system inside the dash. normally the 'default' configuration is to the defrost-vents when there is a problem. there is a vac-motor that controls the air direction within the plenum. that motor either sends the air flow to the dash registers or lets it pass downstream to the floor/defrost motor control vents. the panel door vac motor has a blue hose to it from the function control selector. the downstream 2-circuit vac motor has a red and a yellow vac hose to control each vac circuit in that motor. there is also a white vac hose to the outside air control motor. first thing to check is the vac check valve on the firewall in the engine compartment to make sure vacuum is reaching the function control panel.

 

Thanks for the reply. Is there a way I can manually change over from the dash vents to the defroster?

 

XXL Supreme,

I just used the "search" feature at the top of the page and found many threads on this subject. Try using "vacuum defrost" or "vacuum vent", etc. It will make for some interesting reading. Hope this helps!

 

If the vacuum control is inoperative even when you manually move it perhaps the hinge is broken.

 

I disconnected the vacuum line exiting from the vac check valve and the idle went way up and I could hear the vacuum leak. I re-connected that vacuum line, then disconnected the vacuum line going into the vac check valve and there was no vacuum leak hiss. No matter what line I disconnect, there is still no air blowing out the defrost.

So much for defaulting to the defrost in the event of a vacuum leak.

Also, when I manually move the lever on the check valve the defrost does not blow. Moving the lever does not do anything.

If I replace the check valve should this solve my problem?

 

Where would I find the hinge? Is this a hinge inside the dash that opens and closes doors from defrost to heat?

 

Check for vac from the check valve to the vacuum manifold behind the function control. There is always vac to that control. The blue hose from the function controller should not have vac when the selector is in defrost/floor. If there is no vac at the blue hose then I'd say the panel door is jammed. Find the vac motor in the blue hose circuit and the panel door has a vac line attached.

 

 

Parr4, could you PM a larger copy of that diagram? I am having the same problem.

 

As was illustrated the door is inside the ductwork.
The hinge can break or some debris can get in there and jam the door open or closed.
My '87 truck is of a later dashboard style but I'd imagine they are similar inside.

If in your truck you can access the heater core from behind the glove box it is easy enough to see the door in question.

Reps to parr4 for the excellent diagram.

 

for those of u having the trouble of no defrosters and the dash vents blow constantly i have your fix inally i tor my whol dash apart and found its not a vacume leak. heres a link to youtube of two shrt vides i mad to show whats wrong and how i half assed it to geater for know
hope this helps u all

 

Ironically, I logged in to FTE this evening to troubleshoot the same problem. Today must be the day to fix defrosters in vintage Fords, as I've lived with no defroster for four years.

This afternoon, I verified that all of the vacuum lines were intact and I could see the actuators "working", but the air continued to blow out of the dashboard no matter what setting I chose. (Fortunately, that is not such a bad thing in Texas.) I'll dig deeper tomorrow, but now I'm 90% certain that I will find a broken hinge.

Thank you everyone for your wisdom!

 

I forgot all about this thread. I ended up taking my truck in to have someone else repair it. He said there is a "right way to do this and a wrong way, and the wrong way is a lot cheaper".

He cut a hole in the glove box and wired the door open so the defroster is on all the time. I only drive the truck in the winter so it works for me.

 

He's right, the wrong way IS a lot cheaper. But sometimes the wrong way isn't always the right way.

The blend door cable on mine broke, meaning I couldn't control the temperature of the heat blowing out. So, I popped the hood and wired my blend door open at the little swivel where the cable attaches on top of the heater box. I've still got the lever that controls the function from defroster to floor vents, but the blend door is permanently open on hot.

I also only run the blower on high. It's either high or off. LOL.