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Not to hijack the original post, but i have a similar / related question and thought better of starting a new thread.
My ESOF stopped working a few days ago and defrosters came on full time (whether switched to 4WD or not). After some troubleshooting with a vacuum gauge and fixing a few questionable hoses, I found that the PVH solenoid inlet (the lower vacuum hose connection connected to the vacuum reservoir through a red hose) simply vents to atmosphere all the time. Attaching a MityVac or even sucking on it the old fashioned way, and I can draw air right through the PVH solenoid.
As a result, the vacuum pump can't build vacuum, and ESOF and HVAC doesn't work.
Fine, I think, and pick up a new PVH solenoid at the Ford dealer. Back at my shop, it holds vacuum at the inlet, like I imagine it's supposed to. Pop it on and voila, everything works... For about 30 minutes. I stopped for fuel and when I restarted, same old symptoms returned. Checked the PVH solenoid and once again, I can draw air unrestricted through the inlet port.
I worked around it by disconnecting and plugging the hose that normally connects to the PVH solenoid inlet and just manually locking my hubs. HVAC now works fine and the vacuum pump goes off a minute or so after startup, both of which mean that the rest of the vacuum system is sealed and working properly.
Here's the question: Could I possible have a brand new PVH solenoid that failed just like the old one? Could the very cold weather here lately (-9F or so in the mornings) be causing even a new PVH solenoid to misbehave? Has my wiring harness gone funky and started nuking the PVH solenoid somehow (it passes the normal 'check for clicks by grounding the outside terminals' test). My spidey sense is tingling. It doesn't seem likely. What am I missing?
2006 F350 King Ranch 6.0L CCSB
Last edited by 06kingf350; 01-30-2014 at 12:48 PM.