2000 E430 A/C Problems worked last fall but not now?! Wife upset!!

[ljfIV]

I'm new to M/B but have a fair working knowledge of cars in general. My wife and I purchased a 2000 E430 last fall to replace her 99 accord that was totaled by a 17 year old driver ( rear ended her while she was sitting still) the a/c worked fine, heat was hit or miss all winter, driver side had heat passenger side blew cold or just the opposite. When climate control is activated we now hear a hissing sound in the center vents and once again no a/c. Whats up??? Is there a fix short of taking to a dealer and taking out a mortgage for this repair?? HELP!!!