hey guys i have a 84 z28 and i just dropped in a 350. when i turn the heater on it only blows from defrost. i've learned it switches off vacuum. which vacuum hose do i need to hook up and to wear? thanks

There should be a hard plastic vacuum line on the firewall near the HVAC box. hook it to manifold vacuum, that should do it.

thanks i just went out and tried that one. it works great now. thanks

sorry to bring this topic back up. I am having this same problem, are you talking about where the big thick set of wires comes through the firewall and there are 2 really small hard plastic lines coming in? One goes to the bypass(which I removed) and one goes to the back of the throttle body? I need help, only my defrost works. Also the cruise doesn't work, could these be connected?