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Ford Truck Club Forum > FORD F-250 | F-350 SERIES | SUPER DUTY > 1948-1986 Ford F250 | F350

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Old August 1st, 2017, 12:00 PM
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Default 1984 F350 4x4 6.9 ac stuck on defrost

Like the title says for some reason my blower only blows out of the defroster!
I change settings but stays the same.
Can some one point me in the right direction?
Old August 1st, 2017, 10:53 PM
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I don't know when Ford started using vacuum operated HVAC controls, but on later model trucks this can caused by the lack of vacuum to the system. Trace back the vacuum lines, you will probably find one missing, disconnected, or broken. Another possibility is a stuck blend door or bad blend door actuator. The dash control head could be shot.

If it's cable operated, the cable could be disconnected or broken.

Note that diesels have a vacuum pump, there is no manifold vacuum like with gassers.

2003 F-150 XL RCSB 2wd 4.2 5 speed 3.55 LS
Old August 2nd, 2017, 06:25 AM
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good advice above ^^

I had a mouse make a nest and block the blend door
look for dropping on floor board and under hood to rule this out

For Those Who Fought For It...
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Last edited by JSoko; August 2nd, 2017 at 06:45 AM.
Old August 11th, 2017, 09:08 AM
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thanks to everyone who replied!
I found where a vacum line was spliced and when I squeezed the joint the vent worked so I found the problem!
I will put a gasket sealer around the ends of the connections and that should take care of it. Thanks again john

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