I bought my 87 Z28 with a swapped 383 in it. The previous owner cut the 2 hvac vacuum line going through the firewall. Does anybody know what these to lines control?. I figure one is for the blend doors and the other is for A/C.

 

I’m not sure what the second line is for I think there is only one line for the hvac.

 

One line goes from engine (vacuum), thru the firewall, to Hvac controls. The other comes from the hvac full cold (hot cold/selector) valve and goes back thru the firewall to the heater control valve (to bypass the heater core).

 

What dead said.

One is vac supply to the HVAC control head; the other is vacuum from the control back out to the heater control valve.

 

I sounds like the po removes a lot of things. If the heater valve is still there here is what it looks like.

 

Ahhhh mine doesn't have a heater control valve. Guess its time to get one.

 

Yeah he removed all kinds of stuff. I mean if its a street/strip car make sure the heater works.

 

If you cant find one, just run the lines directly from the waterpump and skip the control valve. Itll be just like almost all of the other cars out there that circulate thru the heater core when the pump is turning.

 

Rock auto has them
https://www.rockauto.com/en/catalog/...ter+valve,6860