Since I have the very same problem, I have spent over $1000. and many hours trying to find the cause.
ECU: tried a brand new one on, no change.
MonoValve: Replaced.
Air pump tested OK, good air circulation.
tem. sensor: Tested OK.
Tried to fool the system by blowing hot air from an hair dryer through the air intake. system responds perfectly by blowing hot hair through the air intake. Full cold blast on automatic.
My mechanic (doing only Mercedes since 25 years) is baffled.
My Mercedes dealer spent 7 hours of diagnostic @ $85.00/hour (testing and trying replacing different parts) and admitted he had no answer.
Very strange.
jackD