Replaced the motor in my 71 malibu with a fresh 350. The car originally had air-cond. but did not reconnect it. The heat works fine but blows out of all the vents including the defrost.I cannot control the defrost,heat ,vent,etc.Is this a vaccum or mech. problem what did I forget to connect.

Probably vacuum related. On the AC box is a small can that has a vacuum line from the intake and another one that goes to your ac/heater control. Did you reconnect this after the engine swap?

I agree that you need a proper vacuum connection. The default mode for these systems is to go to defrost and open the water valve if the vacuum signal is lost. This is done for safety reasons.

In reply, I did not reconnect any vacuum lines from the ac box.Can I hook up to a manifold sourse with a tee?Thanks-Paul