So I know that I have a vacuum issues because no matter what I have the vent selecter set to air will only come out of the defroster. I also am pretty sure I know where the vacuum leak is. The rubber vacuum lines for the locking hubs are old and cracked and are actually not connected to the front axle. My question is if I cap off the auto locking hub lines will that stop the vacuum leak enough so that I can once again use the vent selector? Or is there something else that I can do. Let me know what you think.

 

Absolutely. Anything to stop the vacuum leak should allow the A/C accuator motors to work again

 

I'm not sure what year you have. My 2000 had the same problem. The vacuum pump and res. on the pass. side engine compartment builds up when you turn the key. My front hubs didn't work any longer and the vacuum would never build up. The defrost is the default position and the heater/ a/c needs the vacuum to actuate. I just plugged the ports that fed the hubs, and all is well.


2000 F-350 7.3l Crew cab dually

 

Mines a '99. Where did you plug them? At the point where it enters the wheel well or did you do it at the pump/res. And what did you use to plug them? Thanks for your time.

 

I plugged them at the pump/res. I'm not in front of the truck, and sorry, I don't recall what I used. But any "plug" that will stop the leak will work. I'm sure that most parts houses will have rubber fittings/sleeves that slip over a vacuum line connector that will work.
If you still need help tomorrow, I can revisit and see what I used.

 

Hope im not stepping on any toes reviving this thread but Im having this problem as well however my truck is a two wheel drive. The hoses dont look bad, also upon initial start up sometimes the vents blow the ac but after while itll switch to defrost.

Any advice???

 

Sounds like a vacuum issue. The electric vacuum pump is known to go out and that could cause your problem. Below was posted awhile back from a fellow FTE, that might help you understand it.

 

is there any way to test the pump? I have a friend with a hand pump but wont be home til tomorrow.

 

there is a tsb about a blend box sticking problem .(maybe)