I can’t switch from vents to defrost

[Team Dirt]

83 F-250 and I can’t get it to switch to my defrost vents. The front slider moves fine. I think something is unhooked but I just can’t find any rods that aren’t hooked to anything. Anyone know where the selector is in the dash?

 

[riphip]

I believe your's is like my 86...vacuum activated. The control is on the rear of your climate controls. Is your brake petal hard or dropping when braking? Could be Vacuum pump, broken blend door, bad vacuum control switch behind climate control or something as simple as an item has fallen down the dash defrost vents.
Mine was the broken blend door & not fun at all.

 

[Team Dirt]

I believe your's is like my 86...vacuum activated. The control is on the rear of your climate controls. Is your brake petal hard or dropping when braking? Could be Vacuum pump, broken blend door, bad vacuum control switch behind climate control or something as simple as an item has fallen down the dash defrost vents.
Mine was the broken blend door & not fun at all.

My brakes are not the greatest. Got to really push the pedal to get any action. Maybe vacuum pump is shot. I know my 96 had a vacuum leak and wouldn’t switch to ac but that was a 460. Wasn’t sure if the old 83 6.9 would be similar. Thanks I will check that out.

 

[riphip]

I would check VP first. Good sign of it being bad when you have trouble with both. Try to find a new Motorcraft.
https://www.amazon.com/Motorcraft-BRPV3-Vacuum-Pump-Filter/dp/B001CA76ZY
$131 is best price I've seen & may pick up an extra from here. This comes straight from Motorcraft warehouse

Check over your vacuum lines to make sure there are no cracks, bad hoses, brake Booster check valve or holes rubbed in the lines. Pick up a vacuum gauge. Should pull 21 or better while running & hold after shut-down.