" The Change-Over valve only passes vac' signal to the flow valve briefly when grounding the valve on and off quickly. To get vac' to 15 inches or better, on/off with jumper to ground and it builds up in 1/2 inch increments.......if you apply 12 vdc to inboard pin and ground the other pin, no va'c' will pass. Vac' only passes during the very brief period the ground pulls the Change Over valve 'on'. If it is 'off', no vac' passes and if it's held 'on,' no vac passes.......? "

This does not sound right. The vac sol should apply vac to the control valve at some point and block it at the opposite not ratchet things up. There has to be a vac hose routing problem.

Have a look at club202.com someone there might have a routing diagram.