I just did the dreaded heater core and now have a problem with the center vent. Fortunately I did not put it completely together, just far enough to check out the system. The dash and all the related parts are still on the side yard.

The flap for the center vent opens but there is no air movement. I spent half a day checking things and finally figured out that if I apply vacuum with a hand vacuum pump to the blend air flap that I get flow out of the center vent. This is a problem I created as it worked fine when I took it apart. I have two control heads and two switchover valves, changing either makes no difference. I have no access to any operational information so am guessing by the name that the blend flap controls outlet temperature.

Does anyone have an idea what I might have done to create this problem and if not all else failing what happens if I tap the vacuum line for the blend air flap into the center flap actuator so that they both open and close at the same time.

I made the mistake of giving the car to my granddaughter as a throw away first car, if I had not it would have made its final trip to Pick a part when the heater core started leaking. It is a 94 north of 280,000 miles and is virtually worthless