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Discussion Starter · #1 ·
2002 E350 PSD. Cargo Van. Heat/AC blower has defaulted to defrost. Blower works fine but it is impossible to change the output selection. As near as I can figure from searching the internet, this is symptomatic of a vacuum leak. I have vacuum presently at the manifold on the firewall. The brakes etc. work just fine. I have vacuum at the first junction up under the dash on the rider's side of the doghouse. The black line coming through the firewall then goes out of sight and the next opportunity to visualize the vacuum system is through the access hole in the top of the dash where you can see the lines coming out of the selector switch. I have no idea where to first check for leaks or how I diagnose the problem. There are red, yellow, blue, white and black hoses coming out of the selector switch and going to various vacuum servos located under the dash, none of which currently work. i'm certainly not the first person who has gone down this road.

Yardbrew
 

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Although your van is mechanically arranged differently than my truck, Ford usually uses the same color for each function, so refer to this diagram:

 

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Discussion Starter · #3 ·
Wow! Thanks Steve! What a great resource. Yes, I believe my climate control switch is the same as described in your reference URL.

I found a video showing a guy who had the same problem in a club wagon and just bypassed the under dash connections and junction block with a new hose coming directly from the firewall vacuum manifold and straight to the climate control switch. It worked for him. So that is out there as a possibility. At least that is a diagnostic tool for sure. With your diagrams I can probably isolate the leak (if that is the problem).

Yardbrew
 

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Discussion Starter · #4 ·
Ended up cutting the black intake vacuum just inside the firewall and running an 8 ft vacuum hose straight from the engine compartment manifold through the rider side window to the black vacuum intake on the climate control switch. Started the engine and suddenly, everything works just fine. So, I simply threaded a new rubber vacuum hose through the same hole in the firewall that was used by the existing vacuum line. Hooked it up to the intake vacuum line that I cut. I know that this has bypassed the vacuum tank hidden somewhere down in the bowels of the fender well and the check valve that leads to the tank. If I run into a problem I can always install a check valve and a volume tank up somewhere beside the heater blower.
 
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