I recently picked up a '99 F250 Super Duty with the 6.8L V10 for a song.
The 4 wheel drive hubs are not working with the vacuum. If I use the manual lock on the hubs all is well. I ordered the Innova 31703 CarScan OBD2 + OBD1/ABS/SRS Scan Tool. It says it does Trans codes. I am hoping it will cover the 4 wheel drive too.

I'm lost here any Suggestions??

Maybe related, the heat is always on. Meaning I feel heat at my feet when the temp dial is cold and fan is off. I can't find the heater control valve to check the vacuum line.

 

I don't think a scan tool will likely help. There are a lot of places where there could be physical/mechanical damage preventing the vacuum actuated hubs from engaging. It is not uncommon for these hubs to fail at age. I think a good first test is to determine if you have vacuum at the hubs or (due to your other heating problem) further up the line. That's going to take a good flashlight/shoplight and a lot of patience. A google search will yield a few schematics to help get you started.

 

I have vacuum to the hub actuator solenoid on passenger fender. And the manual says there are codes for the electronic 4 wheel drive.

 

That is the same vacuum line that tee's and goes into cab.

 

I just went through this with my 06 V10. ESOF switch checked out fine. I DIDN'T have my A/C coming out my defroster vents. I had vacuum to my PVH valve on my fender & had 12.48 volts to the center pin. What I did find that no one ever mentioned - was the vacuum line that ran from the Pulse Vacuum Hublock valve down the frame next to the starter & EXHAUST MANIFOLD was melted in half by the exhaust manifold. The plastic vacuum tubing melted together so there was no hole for the vacuum to escape therefore I never had vacuum loss to the A/C diverter door when the truck was in 4WD and the A/C was on. I ended up going to Auto Zone and picking up some 3/16" armor clad (black) hard brake line, cut off the flared ends, deburred the inside of the cut brake line, bent that up to run from just shy of the PVS switch (or valve) to where it T's to go to both the left & right hubs. I ran some heat shrink tubing around the factory plastic tubing shoved that inside the brake line slid up another piece of shrink tubing and heated that also to form a tight seal and everything works perfect now. Using the black armor coat it all blends in and it all looks factory. I used the factory clips that held the factory plastic tubing in place and used small black zip ties to hold my bent up brake line in place and no one can tell it's not factory.
Prior to doing all of this I did check all the vacuum lines from the PVH valve or switch and all looked fine at the time. I removed the locking hubs, cleaned & greased them with the red high temp grease. It wasn't until I pulled one of the rubber vacuum lines off at the hub and used a MightyVac and found a vacuum leak that way. I had no vacuum loss from the PVH valve to the hubs because as I stated earlier the vacuum line melted together at that part. I was going nuts trying to figure this out. Everything now works as it should.
Hope this info is of some help to you.

 

That's a good thought. I replaced the vacuum line from the hubs to a connector at the inner fender. I will try to check the entire line from the PVS switch to the hubs. Is there a diaphragm in the hubs to go bad??

 

Here is what I found. Vacuum to PVS switch is good. Vacuum lines to Hubs are good. I get a vacuum signal to both hubs. Higher for engage and lower for dis-engage.
The left, drivers, hub will not hold a vacuum. I guess it is time to remove the hub.

 

Pulled off hub and took it apart. The big rubber boot inside had a tear in it. I will look for a seal kit or new hub.

 

I can't find a seal kit, only the outer o-ring. Any suggestions???

 

You probably need to buy a new hub, or at least a junkyard hub.

 

I am going to get a new hub from Rock Auto. They have the best price, including shipping.

 

Put in the new hub and it still has a leak. Tried both hubs on both sides and both work on RH side but not left side. I pilled the hub and found gunk in the needle bearing on inboard side. I do have a very slight growl on left side. cleaned it all up and lubed the bearing and replaced the big o-ring. Still leaks. I guess the next step is to replace the axle/knuckle seal. Fun fun.

 

Sounds like a lot of fun. I went through this on my F150 & it turned out to be a bad IWE actuator. I ended up getting a kit installed that included both front hubs and the solenoid on the firewall. I'm not sure it the F20 has the same setup. My actuators were only leaking when the wheels were turned in a full lock position.

 

OK, it's done. New seals on drivers side and it works!!! I think I will do the other side because I can see the seals are not in great shape. A ring has broken off the knuckle seal and is just spinning around.

 

I went though this with my new-to-me 2008 back in July- I too only did 1 side ad thought the troubleshooting was a lot easier than everyone makes it out to be-
Did you get the seal kit at Ford? I was surprised that 50 bucks or so bought all of the o rings and the big donut seal. I also sprung for the new dana axle tube end seal to eliminate the rubber band dangling around the axle shaft.
AP