I am experiencing problems with the auto 4x4 function on my 2004 F250 Diesel Lariat. Hit the sand pulling a fifth wheel down to the beach and the fronts wouldn't lock in. I had to manually lock the hubs and turn the switch to 4low for them to work. At the same time my air conditioning stopped blowing from the dash and started blowing through the defrost ports. WTF?? I've seen other threads that talk about the 'O' ring on the hydraulic unit (I thought these were electric??), or the motor on the transfer case, or a unit behind the glove box. Anyone have any insight as to what would cause the 4x4 and air conditioner failure at the same time?:santa:

 

I hate my electronic 4X4 switch. It's stupid and pointless. My father's truck has the mechanical lever and it is awesome. Yank it and it's in.

The only similarity I know is the vacuum pump. I think the locking hubs are vacuum operated. But I may be wrong. Mine doesn't have a vacuum pump cause it's a gas.

 

You have a vacuum leak somewhere going to your front hubs. There's no hydraulic systems here... Or O rings.

 

I have a 2003 F250 diesel. The only problem that l've had with the 4WD is after replacing all the balljoints. There are tiny vacuum hoses that run down to the hubs/axles. They can get loose or separated at the connections behind the front tires. Also, if you get deep into any front end work and have to remove the axles there is a front axle seal kit needed for the 4WD that must be REPLACED WITH NEW seals. They can't be re-used. New are about $150 from Ford.