I know this subject has been covered before, but I thought if you lost vacuum, the vents would only go to defrost, and not floor.

On my 97, I am able to change from defrost vents, to floor vents, but I am not able to go to mid level, or dash vents. Is this what typically happens when you lose vacuum, or have a vacuum leak?

I removed one of the vacuum hoses near the cowl, and it felt like a normal amount of vacuum. I have not yet attached a vacuum gauge or traced down every hose for leaks. I was hoping someone could describe how the vent system operates, so I would understand it better.

Thanks.

 

A partial vacuum leak will cause partial problems.
Easy way to tell if you have leaks is to let the truck sit for 5 minutes after running then disconnect any vacuum line.
If you don't hear a hiss you have a leak.
A leak free system will hold vacuum for hours if not days.

 

Thanks Bill. I will try that. This weekend I checked several things. I confirmed the 4wd is engaging, and works. The cruise control works. The lowermost vacuum actuator under the dash, which selects between defrost vents and floor vents works fine.

The verticallly mounted actuator, which directs air to the dash vents does not work unless you help it. It needs help getting started and then it holds dash vents open. After cutting truck off for a while it releases and closes the dash vents off again.

Does anyone know what amount of vacuum the truck should be pulling?I could put a vacuum gauge on it. I wonder if I could apply vacuum to the system with the truck off, and listen for leaks?

 

The actuator itself should hold vacuum too, and is easy to test with a vacuum pump. Once you've applied enough vacuum to it to move the diaphragm, that vacuum should hold. Sounds to me like the actuator is leaking.

 

X-2