[shelbert]

I just went through this as well and this is what I learned;

The can gets vacuum from a source as you have done from the manifold.

The yellow line you have run into the cab to the vacuum switch on the a/c controller is correct, (The switch is plugged unless the top lever is in the A/C position. Some of the controls had 2 plugs, some had 3 either way when the A/C switch is in the A/C position is applies vacuum to the other 2 ports in your case.)

The That vacuum is applied to the actuator under the dash near the passenger side kick panel (either of the 2 vacuum prongs it doesn't matter). The 3rd or last vacuum prong line is ran back through the dash to the heater cut off valve and the under the hood actuator. (you will have to T these as well)

I did not however do that with mine, I blocked my 3rd connector off at the controls and put a T under the dash running that one line to both actuators and the heater control valve on the inner fender passenger side. Either of the 2 ways will work.

What this does for you is if you turn on the A/C it shuts the arm under the cowl vent just under the windshield outside (not allowing hot outside air into the cab), at the same time the vacuum closes the heater control valve (turning off the flow of hot water into the heater core to prevent the cold air being heated by the hot coolant water) , and it opens the kick panel vent under the passenger side dash allowing the internal air to recirculate inside the cab for easier cooling.

You should see all this happen just by turning the slide on the control to A/C. Listen carefully when you do it, you will hear a vacuum leak if there is one, also the actuator actuators may be bad with a cracked seal ( one of mine was and it prevented it from opening).