I swapped out my 305tbi for a 350 bored and stroked carbed. in the process of taking the old motor out i broke off what i suspect is part of the hvac controls. theres 2 hard lines comming out of the firewall that were plugged into a valve that had another vacuum line going to the valve that controls water flow to the heater core. my question is what do the 2 hardlines comming from the firewall do, and what is the valve called they were hooked up to (its destroyed and missplaced). i can get pics tomorrow.

 

One is the vacuum supply to the HVAC controls, connects to the intake manifold.

The other is for the heater isolation valve, that cuts off the coolant flow to the heater core in max AC mode.

I can't help in how you would tell one from the other, other than tracing them down. Maybe someone else has a decoder ring they can loan you.

 

so one line goes to the manifold and the other to the heater isolation valve? thats what i figured in the first place, but just wanted to make sure. theres only 2 lines so its a 50/50 shot on which one gets plugged where.

 

A Mityvac might help.

 

do you happen to know if the heater isolation valve has a constant vacuum untill the ac is switched to max, or does switching it to max ac send a vacuum to it?

 

One is for your vent controls and the other is for the hot water shutoff valve. The one with the 90 bend on it is for the vent controls. I just rewired all my blower controls and hooked the vents up yesterday. Hook it to manifold vacuum, if you dont know just try each one and see. Next I got to put a heater core back in and hook the heat back up.

I tried the mityvac didn't work, just hook it to manifold vacuum to find out.