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Discussion Starter #1
I have no defrost.

Fan spins at all speeds, unless the vent controls are on Defrost, then it turns off. Outside of moving the slider off Defrost so the fan spins again, there are no changes to the various vents when I slide the lever, it always blows through the dash vents, which is great for keeping people warm, but not so good for keeping the windows fog-free.

I pulled the heater unit and watched the motion of the actuator, and it seems to move through it's complete range. Nor do I detect any signs of a vacuum leak (hissing, loose hoses, etc)
 

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yo B,
Here is the bottom line;
In Defrost Mode; with No vacuum to any vacuum "motor" , air Flows to Defroster outlets (& air compr clutch is engergized)
Mix - Vacuum is applied only to Port A of the Floor/Defrost Vacuum Motor positioning the Floor/Defrost Door at mid-position.
Air Flow is split between the floor & windshield.
There is no vac at the Panel Door Vacuum Motor.
This closes the instr. panel registers

So, am thinking that the Floor-Defrost Door is stuck...So. to test, pull & cap or pinch off vac line to the Floor-Def Vac Motor to see if door moves to the Full Defrost position (by feeling air flow).



Off- Vacuum is applied to Outside Recirc Door Vac Motor, closing that door to outside Air.

Normal A/C - Outside-Recirc Door is open to outside air. The panel door directs air to the instr panel registers.
The Temperature Control Lever moves a cable connected to Temp Blend Door that mixes heated & un-heated air

Vent - Outside-Recirc Door is open to outside air, as in Normal A/C.
Vacuum is applied to the Panel Door Vacuum Motor, letting air flow only to the instr panel registers.
In the same way, the defroster outlets are closed by the Floor/Defrost Vacuum Motor.

Floor - The Outside-Recirc Door is Open to outside air.
With No Vacuum at the Panel Door Vacuum Motor.
The Panel Door directs air to the floor outlets.
 

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I'd be looking into the electrical side of it too. find out why the blower turns off.

Also on a side note I happened to notice the green and black colors on your bronco. looks good!
 

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Discussion Starter #6
Thanks all. I'll be sure to check out all the items you've listed for me as soon as I get some time to check things out. With a four-day weekend coming up, I should be able to get a chance.
 

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Discussion Starter #7
Ok, i've dug into the dash.

Still haven't figured out why the blower turns off on Defrost yet, but I did check the fuses. I guess the next step is to examine the switch itself.

I watched the vacuum switch motor react as I moved the panel slide back and forth, and I see the arm moving up and down.

That leads me to believe the arm is moving though its full range and either the door is jammed in the closed position or the arm has broken away from the door completely.
 
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