86 heater
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Elder User
Joined: May 2005
Posts: 581
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From: Montana
86 heater
i have a 86 F-150 , 300 -6 W/ ac. i cannot get the heater to go to defrost. i took out the cubby hole and radio and checked the dampers and they are working fine. throwing heat but it all comes out the dash vents. is there a vacuum line or something inside the thing where i need to look next. need the defroster. Thanks Dutch
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Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Dutch - Yours is the first I've seen that won't go into defrost. All the others have been stuck in defrost. The reason usually is because Ford apparently set defrost as the default position, so if you lose vacuum to the controls you are stuck in defrost.
As for yours, it sounds like you can't get it to go to "floor" either, right? Just to the dash vents? If so, I can think of four possibilities:
Second, pull the hoses off the vacuum motors and see where the vacuum goes when you move the control. And, move each motor to the other end of its travel from where it sits naturally, put your finger over the fitting to seal it, and let go of the linkage. The linkage should move back slightly and hang there until you pull your finger off, which indicates the motor is good. If it goes back to the other position then the diaphragm in the motor is bad.
Is that clear as mud?
As for yours, it sounds like you can't get it to go to "floor" either, right? Just to the dash vents? If so, I can think of four possibilities:
- Vacuum problem: but that would mean you are also somehow bound up on the doors and stuck in vent, but you say they aren't stuck
- Mechanical problem: Again, meaning the doors are stuck and the vacuum can't move them. Do you hear any hissing as if the vacuum is leaking?
- Control problem: This one is a pain because the controls aren't easily checked. There's a complex chart in the factory shop manual that shows where vacuum should go given the mode the lever is in, but it isn't easy to test.
- Defrost ducts: Any chance the ducting has come loose and the air isn't going to the windshield?
Second, pull the hoses off the vacuum motors and see where the vacuum goes when you move the control. And, move each motor to the other end of its travel from where it sits naturally, put your finger over the fitting to seal it, and let go of the linkage. The linkage should move back slightly and hang there until you pull your finger off, which indicates the motor is good. If it goes back to the other position then the diaphragm in the motor is bad.
Is that clear as mud?
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
On my 1986 F150, the plastic blend door which can be seen to the left of the heater core when the heater core cover is removed, broke loose at the hinge. When this happens, depending on where the door came to rest, the air flow is either directed to the dash vents or is "mixed" and is weakly distributed to possibly all vents [defrost/vent/floor]. Is this what you are experiencing?
If the plastic hinge breaks, and you trouble shoot from the outside [i.e. visual], the appropriate servos and levers may move, but the door does not line up where it is supposed to.
If the plastic hinge breaks, and you trouble shoot from the outside [i.e. visual], the appropriate servos and levers may move, but the door does not line up where it is supposed to.
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