defroster problems on my bronco
 

when i turn on my defroster, the air still comes out the front vents, any suggestions?

There is a vaccuum servo that closes the defroster door to route air to the windshield. It might have died, or vaccuum might be low due to a leak somewhere. Replacements aren't expensive from Ford - they may be the only place to get replacements for those servos.

Check to see if the cable is still connected on the back of the control.

i sort of have the same problem in my 89 bronco, excpet that mine happens when i use the mix option ( the one just to the left of defrost, for floor and windshield) i switch it over to that slot and it barelys comes out the defrost and comes out the floor mostly , id rather it be the other way around. is there some kind of adjustment ?


airrikk17

Cheggie, which vaccum? The one inside the cab or the one in the engine compartment...Thanks for the help...:-X22

i had a 90 bronco and sorta the same problem. you can pull out the glove box and see the wires for the heater sliders to vents. sometimes the wires pops out of the holder, so the slider will move, but not the vents. the wires arent electical and are to the upper left of the heater core housing. might check that too..

Well, it's all kinda the same vacuum. There is a line from the cannister under the hood that penetrates the firewall over by the blower motor. When you shut the truck off with the defroster on, you normally will hear the servo closing because the vacuum dissapates. The next step is to determine which door closes off the vents for the defroster, and watch it try to move when you activate the switch -truck needs to be running. You will need to remove the glovebox or the radio to be able to see the heater case and watch for movement. I can't remember - this vacuum servo might also be on the back of the case, visible when looking up from the floor. The heater fan is electrical, the heat blend door is cable operated, and the a/c /heat/defrost/floor/mix is controlled by a set of vacuum lines. The servos can be tested by a vacuum pump - if the diaphragm is broken, it don't work! They're all about the same, but it might help if I knew exactly which year truck you're working on.
:-X25

I don't have that problem...yet. What I need to know is, when the defroster is turned on, it is normal for the A/C compressor to engage? because I can hear the same sound the compressor makes when the A/C is on.
BTW this weekend I will install the new heater core (the old one was leaking last year, and got to by pass it), do I need to remove the instrument cluster all the way out? or I can remove the core with the instrument cluster on?

Thanks,

Omar 8a_bronco

Cheggie, its a 82 bronco, dealer installed AC system. (if That might help)

I looked in my haynes manual, and I think the vacuum motor for this one is on the bottom of the case, toward the firewall, visible under the center dash. I've never replaced one in this location, but I think they're serviceable with the case installed. My bet is a leaking vacuum servo, as the underdash vacuum lines are pretty stout. I think they're vinyl, so they don't rot. The trick here, is that you should be able to put your hand by the servo and manuipulate the lever for the defrost door. If you manipulate it closed while the blower is on, you should have defroster air at the top of the dash. Someone will have to help you feel for this tho, as you'll be on your back reaching under the dash! Again, this is a likely scenario, don't discount a cracked vacuum line under the hood, or a loose line somewhere under the dash. The system is not that complex - if you look at it for awhile you'll figure it out! I'll be here if you have questions.

Omar - yes, the defroster does engage the a/c compressor. The a/c not only cools the air, but it dehumidifies it, and this is one reason it's used to defrost the windshield. It's also the only time the a/c gets used during the wintertime - so your a/c seals don't dry out. I regularly run the a/c with my heat on - on cold soggy days, it gives you warm dehumidified air. The two systems work independently of each other, so it doesn't hurt a thing to run them at the same time. Heater core is removeable with the glovebox door and glovebox removed - the dash can stay put. :-X22

Thanks a lot Cheggie....!!!!

I have the same problem and I...
 

I had the same problem with my 1980 Bronco.The defroster sudenly stopped working and the air would only blow out the front vents. I could not get it to blow out the floor vent either. I began dismantling the dash, both on the front and removing the glove box. I removed the cover the heater core as well. I removed the floor duct andI checked all the lines,but there were no vacuum leaks.

I determined the door that controls the air flow to the defroster was sticking and at first thought the vacuum motor was at fault. I had to insert my hand into the plenum after I had removed the heater core cover and by feeling, I could tell the floor-defrost door was sticking.When I manually pushed it shut, the defroster and the floor vent would work when the proper positon was selected on the AC/heater control. I removed the vacuum motor--I hope you have flexible tools and small hands--and it seemed to be sticking, so I bought a new one for about $15 at the local Ford dealer.

After installing the new vacuum motor, I had the same problem. reexamining the shop manual I have, I learned my problem might be the hinges on the floor-defroster door. Feeling inside the plenum again, I found to my irritation that the hinge pins had broken off--they are plastic of course. In order to replace this door--provided I can find the part--I will have to completely dismantle the dash to remove the plenum. Screw that, I thought. My AC doesn't work anyway, so I just wedged the door shut and now I have heat and defrost, but no vents. Maybe this summer, when I have a lot of time on my hands, i might take it apart and replace that door.

reply to rafe1269 about defroster problem
 

I have an '85 F150, and I had the exact same problem you're having. I don't know if our heater systems work the same, but the door that switches the air flow between the vents and defrost broke. It's just a plastic door covered in foam that swings on plastic hinges, and the hinges broke. I had to order a new door through a Ford dealership, and it cost me about $32.

door
 

I also had trouble my 1985 f-150, same door , it was labled on a fix thread .MY 1992 bronco same problem with a differnt fix -vacuum line near the blower motor.Turned out to be the white vacuum hosehad holes in it GOOD luck TR :-X25