I was just back there on the weekend so it was perfect timing! I kind of made note of what vac lines headed into the passenger compartment because I have a code set for blend door actuator. I haven't done the fix yet but I do recall seeing that black vac come into the heater somewhere inside the car.
Ya, when it goes to defrost only that's the sure sign that vac is disconnected somewhere.
Also forgot, there is a check valve in that red vac line that the black branches off of. Not that it matters, but I am proud of myself for remembering
