2003 Dodge 2500 Heater Trouble

[superbee]

The heater gets hot, but when you chnage the desired location for the vents it doesn't change. The defrost/floor setting is the worst. If you get it to do both the defrost is blowing good and the floor is hardly pushing any heat out(very weak). If you go to just floor, it works great. The dash vent setting also works good. Any ideas?

[Valv]

Gas or diesel ?

[superbee]

It is a diesel. Do the gas and diesels have different heaters?

[Valv]

Diesels don't have vacuum from intake, they have a separate (and very expensive) mechanical vacuum pump. Check the line from left side of motor to firewall, you should be able to see a small plastic tube, check it's not disconnected anywhere.

But if your truck is a newer 3rd gen Dodge you will probably have electric servos. There's a door that blends upper to lower vent flow, I am afraid it's not going to be a simple issue.