On my 06 f350 4wd, when the hubs are in auto they will not engage but flip them to lock and they work fine. ive looked and cannot find anything unplugged or out of the ordinary.

 

When you switch to 4x4, does the air blow out of the defrost?

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Either the hub needs cleaned up or you have a vacuum leak.

 

That will be a vacuum issue, 99%. Hubs are most likely just fine. Engage the auto mode and answer the above question

 

No the ac doesn't change where it blows out.

 

4wd actuator is bad. It is controlled by vacuum. Had same problem on my 04 6.0. Both hubs would lock manually but not with the switch in the cab. I did however have the problem with air switching from defrost to vent with acceleration.

 

Do you have a handheld vacuum pump that you can test with?

 

Well I have checked all fuses they seem fine however I am not getting vacuum at the hubs so I take it that the actuator has gone bad. Btw I rarely use 4wd so could that cause problems from lack of use

 

It is not necessarily the actuator. Do you have vacuum from the pump?

 

Yes I have vacuum from the pump I tried bypassing the actuator just a min ago an they lock in.

 

I had a relay issue one time that wouldnt allow them to unlock. I switched the 4x4 switch a couple times and it started working again. If i recall the relay was by the vacuum pump.

 

I have had my passenger side vacuum hose come off twice causing the same issue. I would follow the small tubing from the hub up to the connections by the cross member. The "Tee" connection is as strong as I would have thought. Lats time it happened I stuck it back on and used a little heat shrink to keep it there. Been fine ever since.

 

Gave up and got a actuator from the dealer for 45 bucks (worth the gamble) problem solved