Hi there,
The two vacuum lines coming from the bottom of the servo are from a temperature sensitive switch that keeps the blower from running until the engine heats enough to provide warm air. If my memory serves, it allows the blower to run starting at around 135 degrees or so.
Does your AC compressor run when you push the defrost button? If you have a vacuum leak that prevents the AC compressor vacuum control switch #20 from closing, the compressor should still run when you push the defrost button in. The button bypasses the vacuum switch. If you have a vacuum leak, that vacuum switch not turning on the compressor is the first sign of the leak. (The dash AC switch must also be turned on in all positions except the defrost position.)
I suggest you go to:
http://unwiredtools.com/vacuum and download their simplified vacuum diagrams. They are correct, but easier to read than the ones in the factory manual. If you have a color printer, print them in color as they show the line colors, also the valve positions for each operation. (Unwired tools makes a digital controller which replaces that nasty servo unit with a solid state unit that works much better.) At any rate, it is fairly easy to track down a vacuum leak using their diagrams. Usually its one or more of the vacuum "pods", the units that operate the flaps in the air paths, that is leaking. The leak in turn lowers the AC system's vacuum level to the point that the AC vacuum switch won't make, causing the compressor not to run. If the leak becomes bigger, the blower vacuum switch won't make and the blower will stop working. The reason those two vacuum switches are there is to turn the compressor and blower off when the heater control "off" button is pressed. (The buttons only operate vacuum lines, no electrical switches behind the buttons.)