This has puzzled me for a while. I havent dug real deep yet but after scouring the forum I am no more enlightened.
I have a good strong blower everywhere except in defrost. Seems like no matter what, the floor setting is blowing.
I can't see anything off the vacuum lines that would/should actuate the flaps for the interior blower...?
What am I missing on the vacuum diagram? is this actuated by vacuum? any opinion is appreciated....

 

the defroster vents are controlled by a vacuum line off the pushbutton combu control unit. engine intake manifold vacuum goes through a one-way valve then through the firewall, there's a vacuum bottle that looks like 4 spheres in a row, then it goes into the push-button controller, each of the 3 main buttons is plumbed to a different vacuum actuator (floor, defrost, recirc).

if the left button doesn't turn on/off the floor heaters too, then I suspect you have no vacuum to the whole system, or the feed line is open somewhere. best way to test this stuff is an inexpensive little hand vacuum pump called a 'mity-vac'. you can plug it into any of the vacuum control lines and suck a few PSI of vacuum to see if the actuator works, or if the system is leaking.

 

The left button does turn on/off. I can't find the vacuum bottle. Is it behind the dash?
I do own a mityvac!

 

i'm not 100% sure where it is on a 240, but somewhere buried below/behind the heaterbox would be my guess. if you follow the vacuum line through the firewall, you'll likely locate it.

anyways, if the one flap works then the problem is going to be specific to the defroster vacuum circuit, which is simply a vacuum tube from the button-box to the defroster actuator, whihc is going to be up near the top/back of the heater/air box where the defroster ducts come out.

confusing parts diagram of a 240 heater unit. the defroster actuator is #38. I dunno if there's two, or the one works both sides via a shaft.

 

Some stupid little vac hose fell off that I couldn't see.... Truthfully I was looking for something a little more substantial as far as hoses go. Either way she's blowing now!