A/C stuck in EC mode

[bcjm]

I have a 1997, SL500. The A/C is stuck in EC mode (light on). I have read quite a few threads about running the A/C diagnostic program. I turned the key on, set the temperature to 72, hold the Reset for 5 seconds. I can see the 1 and 78 flashing alternately. I assume that is the in-car air temperature.

I can't go up or down to display any other number. I have the single temperature unit. I tried the Auto button, up/down button, defrost etc.. Nothing seems to work. Is my unit defective or I was just pressing the wrong button?

Thanks
Bob