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The reason you can't find it is they did a good job of hiding this one. I couldn't believe it when I looked it up.
You have to remove the Evaporator core housing to get to it.
Then when I went to look up the evaporator core housing it states you have to remove the instrument panel, man I can't belive this!
You want the instructions for all of this or you want to just find a place to mount a add on one?
Can you find the 2 vacuum lines going into the check valve?
I've been able to trace a small diameter, black, vacuum line from the control switch (or more specifically, the vacuum line connector block under the cover on the dashboard) down to where it goes through the firewall near where a front passenger would have their right foot (i.e. on the far right side - from inside the van facing forward - of the firewall. I'm not sure where it goes after that. There is a similar small diameter black vacuum line that comes out in the engine compartment from amidst the A/C stuff that connects to a red vacuum line that then feedsback into a bundle of vacuum lines in the rear of the engine compartment. There is vacuum at the connection of the red line and the black line in teh engine compartment, but none on the black line on the inside of the firewall. What's in-between (and whether they're even related) is my mystery.
Ok see if this helps you then.
You will need to come off the black source line no. 5 and hook you a reservior and check valve like this pic.
In case this is not making sense no. 5 in the first pic is the source vacuum no.5 in the connector pic.
No. 13 in the first pic is to intake manifold vacuum.
This helps a lot. To confirm, what I need to do is:
1) Cut the black line from #5 on the connector (item 16 in the diagram)
2) Install - anywhere convenient - a new reservoir and check valve (items 15 and 14 in the diagram)
3) Connect the other end of the check valve into a vacuum line to the intake manifold.
I'm not quite sure where to tap into the vacuum in step 3 - do you think the small black tube connected to the red tube in the engine compartment is in fact the line coming from the check valve, or something else? I.e. should I disconnect that and use the red tube for the 'intake manifold connection'?
Look at the picture of the connector(3rd item) No. 5 in this pic is the vacuum source (black line)
The connector in this pic is the connector on the back of the control head.
Now run this to a Tee, then hook one to a vacuum reservior and then hook the other part of the tee to a oneway check valve then the check valve to a intake manifold port.
Am I making sense to you?
I think I can figure it out - just not quite sure where to tap in at the intake manifold. It's a jungle of hoses and doodads - and damn hard to reach even with the engine cover removed...