Heater/AC vent control switch vacuum leak - Ford Powerstroke Diesel Forum
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Old 08-28-2012, 05:36 PM
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Heater/AC vent control switch vacuum leak

So there I was driving down the road and I noticed it was a little warm inside the cab...I turned the vent control knob to max ac and heard a vacuum leak. When I got home I pulled the panel off and it sounded like the switch was leaking....so today I replaced it. New switch leaks just like the old switch...so I replaced it again with another new switch from Ford and the second switch has the same issue.

Since its not the switch....what could it be? It leaks on max AC and defrost, I cant seem to locate any vacuum diagrams and not sure where the lines run too and I couldnt find the vacuum solenoid that should control the air recirculation for the max ac and defrost.

Any ideas?

To troubleshoot so far - I ran some short 1ft vacuum line by plugging them into the silicone harness that connects into the back of the switch and jumpered them from the center port where the vacuum supply is and put them to each port manually and there were no leaks. The vents seemed to move through from defrost to vent to floor as it should. I couldnt find the recirculation vacuum solenoid but didnt hear a leak when messing around with the jumper. So the lines themsleves arent leaking and hold vacuum. I also ran some grease around the vacuum connector and it still leaks so I am confused on what the issue is.

Thanks in advance.
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  #2  
Old 08-29-2012, 10:55 AM
Hee Hee, he's doing it...
 

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The leak aught to be under the hood. I realize that you hear it in the dash but look under the hood near the firewall and passenger fender. There is a white (factory) plastic vacuum line that comes out of a Firewall pass-through harness and loops back to the outside air door near the corner of the bay (look for a bunch of cracks in the hose and there is you leak most likely). This plastic vacuum line dries/rots out and then doesn't close the door any more and causes a vacuum leak in the system. Open the pass though harness sleeve and find a good section of hose. Cut off the bad section and replace it with a coupler and new section of vacuum line from a parts store.
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Old 09-03-2012, 05:18 PM
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That was the problem....thanks. I never would have thought to look under the hood for a vacuum leak sound in the cab.
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Old 09-04-2012, 07:37 AM
Hee Hee, he's doing it...
 

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I had the same thing happen. Tore my hair out looking for a vacuum leak under the dash to finally find it under the hood. Now your A/C will work great with the outside air door working again.
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