What's this vacuum canister on a 1980?

[atmafox]

Hey so I have this vacuum canister above my evap canister on my 1980 with AC, no idea what it is but the small tube goes into the cabin and the big one goes to the manifold.

Any help figuring out what this is would be appreciated!

[vangremlin]

Could be for the AC if the car has one.  When the AC is on, it operates the heater valve to cut off flow to the heater core. 

[atmafox]

Hrm.  Odd, since my heater valve is cable actuated.  I know most images show them vacuum actuated so that's always confused me.

I'll get pictures when it's daylight tomorrow, I think something funny is going on here with my system.

[Trooper]

It could be the fuel purge canister which reroutes fuel vapors back into the engine to burn.

http://amceaglesden.com/guide/1980_6_Cylinder,_49_State_with_3.08_Axle

[MIPS]

I'd say cruise control because my canister is in the same location but you should have a medium size hose coming in from the vacuum source and another to the throttle actuator, before going into the cab and to the brake switch with a large hose.

Could be the SelectDrive. On the 82 it draws vacuum from the manifold on a large hose and exits the canister on a small line.

[atmafox]

'80, not SelectDrive and never had cruise. O_o

I think it's to actuate the heater valve after all, turns out my heater valve did have a vacuum line going to it: it was just very stiff and thin enough to impersonate a pull cable.

So I'll have to relocate this vacuum reservoir because it had to be pulled out to make room for a fuel pressure regulator to drive my new carb.  (Weber 32/36).  I'll take and post pictures after everything is done -- as an aside I found a charcoal canister that fits the dimensions of the AMC one and should sub fine except that you have to tee the carb bowl vent and PCV because it's only got one input -- it's meant for an EFI GM truck, I believe.

Thanks for the help, everyone!
-Atma