About what is the diameter
of the rubber tube that you are missing? Is it vacuum line diameter or is it larger? If it is larger then the foam piece is the "aspirator" that makes cabin air move accross the inside air temperature sensor. Can you see the "damper" door moving inside the vent? If it is moving just a little bit then the connector sounds like it is intact. You should then be looking for a vacuum leak. Also, the vacuum line that goes to the defrost actuator ties into the center vent actuator. Try to connect your vacuum testor up to each individual actuator and insure that they work then look for tubing leaks.