Environmental Controls HELP





I have switched to an A/C delete setup and I'm having trouble figuring out the routing of the vacuum lines from the control module on my 77. The vacuum canister to the far left is Heater/Defrost. The canister to the far right is the Outside Air vent. What is the canister in the middle for? My AIM shows and A/C delete setup, but does not show a connection to this middle vacuum can. I'm confused











