70 Dart A/C not blowing hard.

Yea my 71 dart didn't blow good, had underdash ac add-on I unbolted the vents from the underdash ductwork and it was full of pinestraw and leaves, Helped big time, Also theres a round vacume control mounted passsager side fenderwell, That controls the vacume but if it goes from vent to floor, and defroster it's working but if it's leaking somewhere you'll fill little air coming out the defroster or floor or both,Then thats where your loseing fan power