Mercedes Benz repair: Climate control troubleshooting, climate control system, mercedes 300

Question
Thanks so much for your past responses!!

I have a 1983 Mercedes 300 D Turbo whose climate control system is not working.  The blower motor works, but the temperature of the air doesn't change.  Is there a posting of the order in which I should check the components to isolate the problem?

One of the obvious problems is an a/c belt which is visibly loose.  I don't know if it was disabled on purpose or not.  Since the heater is also not working, I hesitate to tighten it up, because it seems like I should troubleshoot from the control unit backwards.  Is this correct?

Thanks in advance for any light that you can shed,

RSCarey

Answer
Suggest you join: http://www.mercedesshop.com/shopforum/forumdisplay.php3?f=15

Here are some links that will help you DIY.

http://dieselgiant.com/repairyourac.htm

http://mbdieseldiy.tripod.com/monovalve.htm

http://www.diymbrepair.com/Climate/