dead climate control in Phoenix

Hello all,
quick question.....long answer. Two days ago air work fine on my 89 300E w/ 170,000, yesterday air worked off and on, today no air at all except when all buttons are out and doing 60mph a little cold air. I've gone through all related threads with very good info, but not sure how to proceed. My question is, without a manual currently does anyone have any suggestions on where to start looking for the problem, step by step preferable. Limited access to all the nice tools that would make this alot easier. My MB mechanic in the area said to drop it off and he'd take a look at it $$$$$$$$. Any help would be greatly appreciated. Huh, I guess long ? too.

There are no almost fixes or guesses when finding out why the A/C doesn't work. Have your favorite service station who fixes A/C inject fluorescein dye into your A/C system. It is a closed loop system so when he shines the light with his special glasses on, the leak will be very visible. Most common reasons after 5-10 years include: bad high pressure hose (rubber/metal), bad compressor, leak in condenser, or bad climate control switch assembly. P.