Several years ago, on my gas engine 2003 F350, I replaced my auto locking hubs with Warn manual hubs.
Recently I am experiencing the dreaded A/C defaulting to the defrost vents under low vacuum conditions due to a vacuum leak. I have isolated the leak/low vacuum issue to the auto locking hub system "vacuum solenoid". Is this piece still necessary with manual hubs? I was under the impression that the hub vacuum system was specifically for the auto hub system.
Did you try plugging the business end of the solenoid?
I checked vacuum before and after the valve and at the main line to the heater control behind the glove box. With the valve disconnected and the line plugged I have good vacuum. With the valve in place normally I have poor vacuum at most all points. Problem is I don't have any real way to check the 4WD system right now with the valve disconnected. I'd need to find some nice mud somewhere.
If the valve is what actuates the hubs, yet you replaced the hubs with Warn manual hubs, why would you still need the valve? Plug the holes and don't worry about it until you can get to somewhere you can test it, but ultimately I doubt you'll need the valve again.
