1979 300SD-ac blowing thru defroster??????
 

Any info on why my ac is blowing thru the defroster?
Does the cd rom have the info to help me fix this problem? Is it something on each ac that goes bad, like a vaccum hose? The ac works well, but makes driving bad. I live in New Orleans, La, and I need my ac. Thanks
would love to get the vaccum routing to check this out.

Do a search. You probably have a vacuum issue that you will need to troubleshoot and repair.

vacuum actuator, vacuum switch/ valve, vacuum line are the usual suspects. Defrost is default when something glitches in climate control vacuum system. Mityvac to test. really small hands to fix. good luck.