Re: A/C and heat only will go out through defroster..
The vacuum line should start on the LH side of the engine inlet manifold.
When you really can't find the line, you could remove the airco/heat control panel and remove the black line from the mode switch. This is the supply line of vacuum to the switch. If vacuum is available, the problem is then not under the hood, but probably with the mode door actuator, switch or line in the dash.