Vacuum Lines on A/C control

[cairopd1069]

Trying to figure out why my defrost want blow.  There are two doors in the heater box below the dash. I can see the one that exposes the heater core and it opens and closes all the way.  The other door that is closer to the front, opens all the way but when it closes, there is still a one inch gap. If the pictures post, there are two or three places on the back side of the a/c control that do not have vacuum lines going to them.  Should all the plugs have vacuum lines connected to them?

[Jason S]

Year model?

[75gmck25]

I have the repair manual for my '75, and not all vacuum fittings have a hose coming from them.  However, It took me quite a while to figure out the diagram and realize what all the notations meant. For example OA/RA means "outside air"/"recirculated air".   

On my '75 there is also a switch built into the temperature slider, and it serves as the Max A/C control.  If the slider is all the way left (position 1) and A/C is on, then you get high blower and recirculated air (max A/C).  If the temp slider is one click away from far left (position 2), the blower operates normally in A/C position and you get outside air.

My manual has a table that shows each vacuum door and whether it has vacuum when the A/C controls are in each position.  I used that table and a vacuum gauge to verify that each door was getting vacuum when needed.  Then I had to lubricate the linkage for each door and make sure all the retaining clips were on correctly.  I also had to repair some of the vacuum hard lines, using small sections of regular vacuum line as a splice.

Bruce