How do I change the heater control switch on my 2003 ram 2500 . it appears to ONLY be blowing out the vents, NOT the defroster or Floor JUst through the vents. I don't know the vehicle well only had it two months My other truck is a 1998 ram I am not sure what is involved with putting a new one in

SOURCE: PROBLEM WHEN SELECTING THE DIRECTION FOR THE AIR

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.

SOURCE: 1998 Mustang - AC blows only through Defrost vents

You probably have a vacuum leak on the passenger side. its a small plastic hose some times they come unpluged from the engine. or brake.

SOURCE: ac will not blow thru ac vents, only thru defrost vents.

if vent doors are operated by vacuum check for loose or broken vacuum hoses in the engine compartment , or check the fuse box for any ac/heat fuses if it is a electricaly controoled system

SOURCE: Dash vents will not blow air. Defroster and floor vents blow fine.

Is it a new vehicle? I had a new vehicle that had the same problem. Answer was that the holes weren't punched out of the vent.

SOURCE: Heat and AC vent problem.

most likley you have a vaccume leak somewhere but also the linkage to the door that that directs the air flow may be in a bind. another possability is the hvac controlls. hope this helps