Those are water valves regulating the coolant flow to heater core. Did you check the connector plug and pins if a poor contact is causing resistance. You can also measure the valve coils' resistance.

The valves are open in rest state and closed with PWM voltage from IHKA (AC control unit). If temp setting is on max there should be no activation / voltage to heater valves.

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey