[tomdel45]

1997 dodge ram 1500 , how does the vents work for floor, defrost etc. I know it works by valcume but is there a pump somewhere. Can not get it to change it is stuck on defrost ( window ) it has some suction but not a lot. How much should it have. Nothing is broke on the controls.

[medic-dan]

The vacuum for the vents comes from the engine. There should be a check valve and reservoir in the system. The check valve is probably mounted near the power brake booster. It's a one way valve and it can fail. Be care of which way it is mounted.

If you've located the connector at the heater controls, on a Dodge the black line is usually from the vacuum reservoir (source). It should have a pretty good suction on it when the engine is running at idle. If not, check the check valve and the lines for leaks.

[tomdel45]

Where would be the vacuum reservior and check valve located?

[medic-dan]

The check valve should be near the brake booster, usually where the large diameter vacuum hose comes from the manifold. They would be a small tap off the line with a smaller diameter vacuum line coming off it.

The reservoir can be mounted under the hood or may be mounted under the cowl.

[tomdel45]

It turned out to be a bad vacume hose at the engine.