I have an 89 f250 with the 460 and factory air. My problem is this: The previous owner was a retard and half arsed everything. I just put in a new heater core and have that working now. My problem is that I can not select any settings on the climate control switch. It is stuck on defroster. I assume its a vacuum problem as I have torn everything else apart. I have a white vacuum line and a black vacuum line coming through the firewall into the engine compartment. The white one is conected to the blower motor houseing fine. The black one is the problem. It is broke and goes no where. Can anyone tell me where this vacuum hose goes? It comes out of the firewall and goes into a splitter so that it terminates in two hoses that are just dangling. Any help

 

old post, but it describes my issue. does anyone know the answer? i'll try to take a pic later today.

 

The one side of the tee goes to a fitting on the side of the heater core box, it's just to the left of the intake plenum on the engine. The other side goes to the left most of three vacuum lines that emerge from the firewall just above the engine intake plenum. The right hose of these three goes to the vacuum tree on the intake plenum, and is the vacuum source for the HVAC system.

 

Yes, thank you. Got 'me all hooked up and I got air coming from all the vents, floor and defrost! Sweet!
Now what I'm trying to figure out is why? The unused ports on the vacuum tree on the intake were capped, like the line was disconnected on purpose. Any ideas? The truck idles fine, I need to take it out for a drive to see if anything has changed.