You'll have to get under the car. On both side of the tranny hump, just about the middle of the tranny are two short rubber hose ends. Those are the evaporator drains. Try cleaning any built up crud from the ends with you fingers, I don't think there will be enough room to use much else. If they aren't plugged, then one or both have come loose from the box and you'll then have to gut the lower dash and reattach the hoses.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.