I have a 99 f 350 duelly and the heater blend switch stays on defrost. Can someone point me to some posible fixes. Thanks Andrew Curtis

 

Sounds like you have a vacuum leak somewhere. Is your truck 4x4? When you turn the key to the on position, does your vacuum pump turn on? The pump is on the passenger side firewall.

 

It's a 4x4 and the pump is not comeing on . Not sure why the pump is not working. Do they go bad a lot? It was working up in till late in the summer how can I check if the pump is bad? Thanks A Curtis

 

Check the fuses. Check to see if the pump is getting power but not coming on. If that is the case, a new pump is in order. Yes, the pump has gone out before for some people.

 

Check fuse #28 15A under dash.

 

After new pump if still on defrost check hub valve same fender more front line in block if blend works problem in lines to hubs or hub seals

 

The fuse was the first thing I checked. I ordered a new pump I'll see if that takes care of it. I think all the plumbing to the hub lock is in ordered. I changed ball joints last year and all the seals with that. The auto lock has been working up till now. Thanks for all the help. I'll post back when I get it fixed. A Curtis

 

I picked up the cheap pump on Ebay 60.00 and free shipping. Works like a champ. Thanks for the help. FWIW If you spray some penetrating oil around the hub selector **** and work them back and forth they get easy to turn.
Andrew Curtis

 

 

Glad it worked out and thanks for coming back to let us know.

Have you seen this yet? Welcome to guzzle's 4x4 Autolock Hub Lubrication Maintenance Web Page

 

I did use that guide last year when I installed new ball joints on the truck. Great info on this site. A Curtis