BMW E39 5-Series Blower Motor Testing | 1997-2003 525i, 528i, 530i and 540i

The blower motor controls the airflow of either outside or recirculated air. When you push the button on your IHKA control unit for the blower motor speed the IHKA control unit sends out an electrical signal to both a blower motor relay and the blower motor final stage. This electrical signal tells the final stage to either spin the blower motor a lot for maximum air flow or only a little for minimum airflow.
If you push the button to change the blower motor speed and nothing happens you may have a blown fuse, a bad blower motor relay or a bad final stage. There have been cases where the final stage has kept the blower motor running while the ignition key is off, therefore draining the battery and leading to a "no-start" problem the next morning. In this tech article we are going to review how to test each component in the system.
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[@MrRobotPower]

Thank you for the extremely clear and detailed explanation. Also very good pacing on explanation and arrows on the video make it crystal clear what you are talking about. Very well done video.

[@pelicanparts]

Glad you enjoyed it!

[@Horrokotoj]

Question: On the FSU/FSR connector should I be reading battery voltage on pin 2 if the ignition is off?
If this is the power supply on blower motor relay it is my understanding that this should have battery voltage when the climate control system wants the blower fan to be on.
Reading battery voltage on this connector would indicate that the relay is stuck open.
Am I correct?

[@pelicanparts]

Should be with the key ON.