I am another one of those individuals having an issue with the dash blower not working. I have read and learned quite a bit about the vacuum system. I traced out some of the vacuum lines and found that the one that was supposed to come out of the ball unit behind the passenger headlight was disconnected at the ball.
I bought this van used rather recently and I do not know if it was disconnected for any particular reason. Anyway, when I picked up the hose a fine powdered sand was coming out. I tapped out what I could and reconnected the hose to the ball. I ran the van a little bit and I was still unable to transfer the air from the windshield area to the dash vents. Here are my questions I guess.
1. Does the vacuum pressure build over time or should I have seen an immediate availability of air through the vents?
2. Will the remaining sand, if any hit a filter somewhere?
3. Where can I locate the other end of that particular tube if I wanted to just replace the whole thing?
4. Would that disconnected hose cause a misfire code for cylinders 1,3,5?
5. Do I need to add a flow check valve anywhere?

Unrelated- Does anyone know where I can get the triangular shaped plastic inserts that are used to connect the headlight to the three screw posts? They snap into the headlight itself and sit over the ball at the end of the screw. Thanks.

Any help would be much appreciated. I am a complete novice if you haven't figured it out already. Thank you in advance.

 

That hose leads back to the engine, and its tee'd off to the HVAC system. The ball back there is a vacuum reservoir. The unfortunate situation you have there is that dirt has been getting sucked into the vacuum hose, and consequently, your engine. Good thing you reconnected it.

Check all of those vacuum lines one by one. The crack, split, and break as they get old and brittle. Had to do quite a few repairs on mine before my vent switch could make any difference to the vent position.

 

So, last night I took off the cowling inside the cab and traced out the lines. I found a couple of connectors that were clogged with the aforementioned sand. I cleaned them all out using a safety pin and water. I blew through all the hoses and connectors piece by piece all the way back to the engine. I hooked it all back up including the original disconnect at the ball. I started the vehicle and voila. Working vent. I am still going to purchase and install the 1 way flow valve unless there is a reason not to.
Like I said, I am a complete novice. All it took was some reading and some patience to trace the lines.

 

Sand inside of a vacuum hose. I hope the sand never made it inside the engine. If it did those cylinder walls could be quite scratched up by now.

 

could bad vacuum lines cause the vent to switch from floor to windshield to dash everytime you accelerate? That is the issue I have with my 98 3.9. Thing is the vent will return to half dash and half floor. It's quite annoying.

 

A vacuum leak for whatever reason, whether it's a crack line, or a ruptured diaphragm inside of an actuator will cause this. The other thing that can cause this is if the check valve is leaking and allows vacuum to flow in both directions instead of just one.

Look on the passenger side of the intake for a single vacuum hose coming off of it. That is the line that supplies the HVAC system with vacuum. The check valve is usually in-line within a few inches of the intake. Note it's direction, remove it and blow through it both ways to test it. If you can blow through it both ways then replace it, if you can only blow through it one way then reinstall it and follow that vacuum line until you find a leak.

 

Thanks Alloro! I will be searching for it this weekend!