Hello all, ive been trying to fix an issue with my 740 gle for about 6 months on and off now and no matter what i do i cant get any air on any settings, blower is fine, vacuum bellows are fine (spent a weekend rebuilding the entire mixer box incl. new felt as a replacement for the sealing foam, refinished actuation rod, all tested and actuated properly. I've tried to take off the cover from the A/C evap and broke it accidentally but from what i can see there is a very small amount of debris which was removed easily with a blower. No idea what else it could be, any tips appreciated.

 

not to be difficult, but did you verify that the vacuum check valve on the firewall is in good working order and the vacuum line to it is not leaking?