Interior heater ac question

There’s a vac line that runs to the flap that controls whether the air goes to the defrost or the vents. If it slips off, it’s stuck on defrost.

look up the left side of the center dash area. The vac line is yellow on fox cars. You should be able to see it go up the left side and connect to a vacuum canister

if it’s connected, you might not have any source vaccum. There’s a single vac line that goes into the engine bay from the heater core area. You’ll want to check to see if this is seeing vac.

that line runs to the hvac controls which diverts the vacuum as needdd. No electrical is involved here