1992 Dodge Ram Van Heater vacuum problem

[831johnc]

After not using the B250 Van for about a year due to heart valve replacement. I find that the heater/air conditioner vacuum motor won't switch the air deverter to the dash vents. All of the hot or cold air goes out the defrost and some towards the floor boards. I've made some checks and don't find any obvious leaks. I've sprayed carb cleaner on all of the vacuum hoses in the engine compartment and didn't find any leaks. I use to be a pretty fair mechanic but at age 72 I find more problems than fixes. I will sure appreciate any help I get from you guys. I'm taking my wife to see her sisters in MO. in about 2 weeks and I am sure I will need the heater and the A/C. Thanks again 831johnc
PS- this is a 318 with TPI

[alloro]

There's really only four possible things that could cause this.

1. No vacuum situation through either a broken or clogged hose.
2. The vacuum actuator that moves the air diverter flap has a leaking internal diaphragm.
3. The diverter switch up on the dash is no good.
4. Mice, squirrels, or other small animals got into the duct work while the van sat for a year and stored acorns or built a nest. This debris is now preventing movement of the air diverter flap.

The easiest way to narrow down the problem is to get under the dash and see if you can move the flap manually and to also test for vacuum at the actuator.

[831johnc]

Thanks, I'll try all of your suggestions.
831johnc

[dieselcaddy]

So what you are saying is that it doesnt blow the air where you want it to? It gets hot and cold like it is supposed to?

Blaze

[831johnc]

Dieselcaddy,
The heater and air conditioner both work as they should. The problem is that they don't blow through the dash except when cruising on level ground or decelerating. The hot and cold air blow through defroster holes and down towards the floor. The engine also idles with a small surge that I would not expect from a fuel injected engine. I have checked for vacuum leaks visually and by squirting carb cleaner on connections. Would a vacuum guage let me know if there was a vacuum leak? Thanks, John

[alloro]

Oh! Well that explanation makes all the difference in the world. Your problem is that the heater vacuum check valve is probably leaking internally. The check valve is a valve that only allows the vacuum to go in one direction and is only a few bucks at a dealer. Take a look on the passenger side of the intake manifold. You'll find a vacuum fitting half way back with a rubber elbow on it and the check valve in the second end of the elbow. Pay attention to it's direction before you pull it off, you don't want to reinstall it backwards.

[alloro]

BTW, you can test it by pulling it off and blowing through each end of it. You should only be able to blow through it in one direction. If the air flows both ways...it's bad.