[Richard]

Hang on, the common symptom of a failed control valve is the fan runs on high all the time. The default mode is high. Unplugging the connector simulates the default mode. Based on what you said, it does not appear you have a control problem.

Do you mind providing details on how did you know the fan did not come on as needed? Overheating? Observed fan not turning?

I am just trying to match what you described against the unplugged fan on behavior.