Lorenfb

If that happens, the CCU thinks the engine is hot and needs to run the rear fan. Typically, the suction fan should turn off (@ CCU turn off) in 5-10 seconds.

ToreB

If the ignition is on for less than 5 seconds, the CCU will indeed shut down within a few seconds.
If the ignition is on for longer than this, the CCU will stay on for up to 20 minutes in for proper cabin temperature regulation at short stops. If needed, it also runs the rear fan in cooling mode during this period in order to reduce the engine temperature as fast as possible.
Depending on CCU version, there might be some variation on the above mentioned 5 second and 20 minute thresholds.
Cheers,
Tore

r-mm

Thanks Tore. And If I understand your site correctly, there is a possible failure mode where the fan will not shut down (ever?) and becomes a parasitic draw?

ToreB

Yes. the internal power supply transistor can cause the CCU to be permanently on. https://www.bergvillfx.com/ccurepair

Cheers,
Tore

Lorenfb

And other internal CCU problems, i.e. replacing the transistor isn't always the problem - not that simple!