how is this done on a 1994 SL 500,factory manual on order.

When climate control is on, press and hold rest for atleast 5 seconds. Press arrow up (air towards windshield) to go the next number up and arrow down (air towards feet) to go down. Do a search to find out exactly what the codes mean. I don't remember off-hand, and mine are probably a little different than yours. Good luck.