Check your Heater Blower Regulator. I had a problem with my '95 S500 - AC was cold but would not blow. I replaced the regulator and it works fine. Takes about 30 minutes, simple R&R job, 2 screws and 2 connectors and you can check / replace your cabin air filter at the same time. You can find the regulator on eBay for around $50 - $150. It comes with a small tube of zinc oxide that you smear on the back of the unit when replacing it to make contact with the housing below, just be sure to wipe off all the old zinc oxide from the housing before you put the new one on.