I recently purchased a 2005 F250 super duty and the four wheel drive seems to work intermitantly. if i lock the hubs it works, I turned them to automatic and it worked for a while. Now im not too sure how this system works, but I know that that it applies vacum in both steering knuckles when you select 4x4. When I select four wheel drive on the dash within 10-15 seconds my heater goes to defrost and remains there until I put it back into 2wd. Hence a large vacum leak. Do the automatic hubs operate on vacum? or is it something different? if it is what does it actuate?
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Auto hubs are vacuumed controlled, i believe... I also think your on the right track with a vacuum leak or something lines plugged up some where...

 

Yes they're vacum controlled hubs.

If it was just the hubs not locking I would say you've got a leak in those lines, but since you've a second problem I would bet it might be bigger or somewhere else in the system. Check in the SD forum about the air only going through the the defroster, I'm pretty sure theres a bunch of threads about the specific vacuum leak that can cause that, and it might be a good starting place.

 

there are a bunch of threads on this problem in the superduty forum
sounds like a vacuum leak on your hubs, which happens to almost every superduty
I dont even use the auto hubs, I manually lock em, dont want to be in some mud and not have 4wd

 

The vacum solenoid that is suppose to realease vacum is working intermitanly. Thats one problem, the second is when I try to pull some vacum on the left front knuckle I can't. so I suppose a seal and solenoid should fix it... for now. the vacum pump will only pull 15 inches, is that sufficient?

 

Your system is apulse vacuum system. It does not require a constant vacuum.
If this was the case, the hubs would disengage if the vehicle were to be shut off. Imagine running in some mud, and stopping for a rest, and turning your truck off, and having your hubs disengage. Bad things, but this is not intended to happen because the huns are pulse activated.
Regardless, the ESOF system is junk at best, and anyone using this system with any type of reliabilty has been plain lucky.
Ditch the entire system for manual hubs, and block the vacuum system. Your climate control will work, and you will have a more reliable 4wd system.
Might consider the Dynatrac system real soon, because the next worse thing on the Sd trucks after the ESOF, is the dumb unit bearings.
What were they thinking?

 

> the ESOF system is junk at best



Ford automatic hubs stunk in the 80s/mid 90s, Ford found a way to make them even worse, even worse then that, they put them on trucks that should not have them and put "hubs" on their abortion Dana 50.

I expect to find hub bearings on AWD vehicles like my Aerostar, non a light 1 ton truck