Climate control

[Marc-1]

1991 300SL
I've asked about the AC not working and I got a great list of instructions for diagnostics, however some of the instructions didn't work. I did manage to see some codes and some temps (in Celcius) and #1 with a little square. Presumed to mean no codes are stored.....................

Here's the problem... When I start the car the 'EC' is lit, the #3 fan speed is lit, the up arrow is lit, the 'F' has changed to 'C' and the air is coming out of all the vents at full force. I push the automatic button and there is no change in air force but all the other lights go out. Each time I also need to reset 'F'. After a moment the automatic works!
This all doen't happen everytime, just 9 out of 10. I sometimes push off and then auto but the AC still doesn't work (no cool air). This just started this year after winter storage. Could the battery be low?
I just don't know what to look for.
Can you please help me with this?
Thanks in advance,
Marc