70 elky vents inop

I can not get the cowl & side vents to work on my 70 elky with AC.The AC works,heater and defrost/deice work.But I can not get vents to open.If I disconnect vacuum harness plug from control unit and connect a jumper hose between black hose(vac feed from engine)to orange hose that goes to side vent and cowl vent,they will open.I figure it's the vacuum control thingy the hose harness connects to.Makes sense.I replace it with a NOS unit that I believe to be good and it does the same thing.I can not hear any vacuum leaks.But it is kind of hard to hear because I have to have engine running to create vacuum supply.Anyone else run into this problem?Thanks,Jim