[fuffi_lwl]

To further check the electronics, do the following: Remove the connector and put a current of 12V on Pin 1. Put Pin 2 and 3 to ground, somewhere in the engine bay. This way, the water valves are shut off, so no warm water should enter the heater core, provided that the seals are in good condition.
Without current, the water valves are open, and thus the heater core always warm.

Pinout as follows:
Pin 1: supply voltage 12V
Pin 2: Ground for the valve on drivers side water circuit
Pin 3: Ground for the valve on passenger side water circuit

If the heating is getting cold after this procedure, the signals of IHKA and so on are wrong.