Defrost only, no vents or floor

Noiseydiesel

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'94 7.3 idi turbo F350 crewcab dually.
Defrost works good hot or cold. I repaired the vac line to the dash and got it working and still no vent switching action. Fan works good, temp change works good also.
Any ideas?
Thank you one and all in advance!!
 

Noiseydiesel

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GEE! You sound just like my wife.
This truck is going on a road trip tomorrow.
Oh well.
Something to look at maybe tomorrow night.
I was suspecting the same but playing ostrich is more fun at times. It tends to just delay the inevitable.
 

Noiseydiesel

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That's the first thing I checked, I was surprised that the line showed no damage but was still plugged, so it got replaced. I then had vacuum going to the dash. Might be getting lost behind the dash, but it is going to the firewall.
 

chillman88

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Are you sure you checked the correct vacuum line? There are two there, one goes in to the dash and another comes back out for the recirculation door.

I'm impressed how many of these still work fine after all these years, being they're all vacuum diaphragms.

I think the main junctions are behind the passenger kick panel or glove box, and behind the HVAC controls/radio. I have a spare dash I could take pictures of, but it's a bricknose so I don't know how much is the same back there.
 

Noiseydiesel

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The main line that feeds those two is the one I repaired. Later on I will pull the dash controls and have a look. I expect an easy fix, even if needing to replace the switch.
Thank you!
 

genscripter

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A long time ago, i had the vacuum selector valve leak on me. Found a replacement in the junk yard. It plugs to the back of the climate control. The leak led to my vents not working. I could hear it leaking when i turned off the van and it was hissing.

What's more likely is you have a vac pressure issue. If you also have squishy brakes, no cruise control, and bad vent control all at the same time, it might be the pump or a leak in the hoses or manifold.
 

Danielle

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Smoke it!

Sometimes it is a crack that isn't obvious. Sometimes it is something that looks plugged in but the end of the hose attached to he port looks like a peeled banana and it is leaking but appears to be attached. Sometimes the T or Y connectors crack at the junctions. But smoke will find it. They're usually big holes on these old trucks
 

BR3

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It's extremely rare, but there is also the possibility that the selector head has failed. It would be the absolute last place I checked as I've never seen that part of one fail before, just the electric part of the head.

As stated above, you almost certainly aren't getting vaccum to the head in the first place
 

Jasonmusic220

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Yeah mine was stuck in defrost as well. I pulled the A/C Heater Control Switch out from under the dash and one of the prongs was dry rotted and broke. Everything looked fine, but the one broke prong caused enough leak to where no vent controls would work. Hopefully you get everything fixed up!
 
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