Heater quits in 4x4

[woody2850]

2003 F350 6L My heater starts blowing cold air everytime i put my truck in 4 wheel drive, when i take it out of 4x4 it starts blowing hot air again. Could this be due to a vacuum leak in the hubs?

[Banshee365]

Yes, you have the dash mounted 4x4 shift right? Have you rebuilt anything in the wheel hubs lately? Check the lines to the hubs as well. Sounds like you have a nasty leak.

[Keith T]

This might help. It is for an 04.

[woody2850]

Yes its dash mounted shift. Thinking it must be the yellow O rings in the hub assembly but is there and easy way to check? I haven't done any work to it since about april when i changed one of the hub assembly's.

[rizzlebizzle]

There is the smaller o-ring around the outer hub, the big o-ring around the hub, and the axle seal that can cause vacuum leaks. My vacuum leak was coming from not replacing the o-ring on the outer hub when I did my ball joints. i could hear a hissing when i turned the key on the truck and only got air from the defrost. To stop it temporarily I packed the whole area where the ring seats with grease and put the outer hub back in. That would stay until the grease dried out, so I bought a new one and no problems. So if you didn't replace those o-rings when you did your hub or removed the axle for some reason without replacing the axle seal those are places to look