Hey everyone. My ESOF on my 03 F250 doesn't work and I have a vacuum leak somewhere. I switch to 4hi and the AC goes to defrost. I changed the hoses from the hub to the frame and that did not fix the leak. Any suggestions on where to go next? 4x4 works when I manually lock the hubs but no ESOF.

Thanks,
TW

 

Most likely a hub leak. Block off one hub vac line at a time. The one that is blocked off that doesn't cause a "default to defrost" means that hub has a leak.

Could be either an 0-ring or the axle seal that is leaking. See this LINK.

 

My hoses and my ESOF module leaked. I replaced the module and cut the ends of the hoses off by about 2 inches (pull from back side of tire, cut, push back on). All is well here.