Hello, My cars A/C has recently decided to become possessed. The lights on the A/C controller randomly come on and off. The blower comes on but is not controllable. The compressor works, but is also randomly working. I keep getting a consistent code of EO 13 for the rear A/C controller. The problem is this is a coupe and does not have one installed.
I completely disassembled the A/C controller and verified the resistance checks on all the control wheels potentiometers. I have all of the buttons now working. I recently replaced the blower motor due to a failed bearing. I had a spare controller suspecting an issue with the harness, but that made no difference.
I do not want to purchase another ACC controller and just have the same issue. Any ideas on this one? Any ideas would be appreciated.

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1989 560SL
1986 300SDL
1983 300D (Burning Jet-A)
1982 240D
1995 S600

Just a follow up incase anyone else runs into this issue: The duovalve has an internal failure. For whatever reason, this is causing all sorts of failure in the electrical system. To include the fan randomly turning on and off, climate control panel turning on and off, zeroing out of of the temperature, full heat, and sometimes full A/C. Disconnected from the system and all is working normal.

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1989 560SL
1986 300SDL
1983 300D (Burning Jet-A)
1982 240D
1995 S600