Where do these two vacuum lines go?

[cardana24]

I am in the process of changing my heater core on my 85' 2.8 V6 cherokee. I have two vacuum lines that I am not sure where they go. One is black and the other is purple in color (not sure if these are the factory colors if it helps). Both of them run though the same grommet in the fire wall, just above the a.c. expansion valve. One of them runs from a valve on the lower heater hose (coming away from the heater core, and then through the fire wall. The other one goes from what looks like a black can (there are two of them side by side) through the fire wall at the same place as the other one. Does anyone know where these two lines go after they pass through the fire wall?? I would appreciate any help.

[Ray Hamilton]

My guess is the "black can" is a vacuum booster. I'm not positive, but how hot the heat is is controlled by vacuum. The more vacuum applied the more hot water that valve will allow through the heater. Apparently you have them unhooked from the inside? You should see some sort of vacuum connections in there(heater controls). Try on one and see if you can hear a hiss when the heater is turned up and see if the def/heater gets hot. The one coming from the black can should be full vacuum.

[SappySE107]

Can is usually the charcoal cannister and the other would be a ball usually for a vacuum cannister.

[cardana24]

My guess is the "black can" is a vacuum booster. I'm not positive, but how hot the heat is is controlled by vacuum. The more vacuum applied the more hot water that valve will allow through the heater. Apparently you have them unhooked from the inside? You should see some sort of vacuum connections in there(heater controls). Try on one and see if you can hear a hiss when the heater is turned up and see if the def/heater gets hot. The one coming from the black can should be full vacuum.

I think that both lines are functional. The line from the vac resivor is pulling vacuum when the engine is running. The line that runs from the heater valve into the cab is hooked where it is supposed to be. When I plug that line in on the heater controls and the A/C is on, it makes a loud hissing noise. I can pull that line out and plug it with my figer it is defiently pulling vac as well while the engine is running. Everything appers to be hooked up correct, what am I missing? Shold I hear a hissing noise when the heater valve vac line is hooked up?