AC/4X4 vacuum leak?

[Bubbalarge]

I've read a ton about this issue but still cant identify my problem. '01 excursion 4X4 shift in the fly. My heat and A/C only vent through my defrost. SOF does not engage my 4X4. If I lock my hubs manually and shift the SOF switch, I have 4 wheel drive and heat through any vent selected. Hubs locked and in 2H mode, heat defaults back to defrost mode.

If I disconnect and plug the vacuum lines at the hub still defaults to defrost.

Brand new vacuum pump installed, hubs removed, inspected o rings and greased.????

[7.34ever]

I know the inner axle seals will cause the SOF to not work but not sure about the whole defrost thing. Anyone esle? good luck

[Cjcross22]

You checked all the vacuum lines to the hubs for leaks and found none?

I don't know what else it could be if you installed a new pump..

[away]

Heater controls

Chaeck this out

[mumby]

had this problem I think. If my AC was on and I shifted into 4x4 with SOF it would change over to defrost for like 2 minutes then back. It was a bad vacuum line. Check them if you haven't.

[STANGMAN893]

Check the vacuum solenoid under the pump mine was bad on my excursion but I had different symptoms.You could put it in 4wd but wouldn't go in for a while and then wouldn't release for a while.

[angus121]

mine would only defrost and no 4x4 and i traced it to a vacuum leak and it ended up being the switch that put the vacuum towards my lockouts. it had stuck and let vaccuum bypass..its right behind your vacuum reservoir bolted to your fender.it was 30 bucks at my local junkyard and took 5 minutes to change..it would be something to check