MONTE CARLO Heater blows weak

[Bludacious]

I have an '85 MC with the factory A/C. Just started daily driving it with a brand new blower motor, whenever I turn the CC to the lower vents (heat) it blasts out full force, but defroster and dash vents are barely a whisper, especially the A/C only one to the left of the gauge cluster. The only clue I've gotten is a thin white vacuum line under the hood that's been snapped since I bought the car in June. Will I need to tear apart my dash (again) to get at the mixture doors, or should I check the lines coming from the firewall? Whenever I switch heat options I hear a clunking after a few secs before I get any air out the top at all.

 

[fleming442]

The only clue I've gotten is a thin white vacuum line under the hood that's been snapped since I bought the car in June.

You answered your own question; the vents are vacuum controlled.