Ok, here is my problem: My truck will only blow air out of the defrost vent. It doesn't matter which selection I have chosen (Max AC, Norm, Vent, etc.), it still blows out of the defrost vent. The only other setting that works if "off". All the blower levels work fine, and the heat adjustment works fine, but either I have no air flow, or all air flow going through the defrost vent.

Is it just my selection switch that needs to be replaced?

Any help is appreciated.

If it matters, its on an '04 F-250 6.0L Supercab.

Thanks in advance.

 

You have lost the vacuum feed from the engine to the HVAC control switch.

You're in the default operating condition.

Steve

 

i agree somewhere u have a vacume line off it happend to me and when i had it serviced the dealer hooked the vacume line in the wronge place, somehow i figured it out myself. i moved the line a it went to working norm

 

Thanks for the quick response guys. Are there any hoses in particular that are notorious for going bad, or is it just a job where I start checking each hose until I find the problem?

Thanks again,

Brian

 

There is a single vacuum hose that runs through the firewall to supply the HVAC control. It is routed behind the battery and has connections for a vacuum reservoir (in the passenger fender), a check valve, and some other tees. It commonly rots though right in the area of the battery. Also, the check valve can fail and leak, or the vacuum reservoir gets cracked, especially if the truck has been in any collisions.

Look between the battery and the firewall first.

Steve