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The blower motor module translates a PWM signal from the ATC module into a blower motor speed selection. Current control to the motor is established through a resistor pack. The back of the control module (the side which goes into the heater assembly) also functions as a heat sink to dissipate the heat generated by the resistor pack. The airflow from the motor dissipates the heat. The blower is a DC motor. The only way to control the speed is by varying the current, and since the incoming voltage is always 14vdc you have to change resistance to change the current. It's Ohm's Law. Simple stuff.
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1) The only way to control the speed is by varying the current,
2) and since the incoming voltage is always 14vdc
3) you have to change resistance to change the current.
4) It's Ohm's Law. Simple stuff.
1) This is a reasonable way to look at the motor control
2) No
3) No
4) OHM's Law isn't violated but that doesn't mean the circuit design has to be simple
The PWM (Pulse Width Modulation) is used to turn the Voltage on and off. Using your assumptions 14 Volts and then 0 Volts. By doing this the current can be adjusted and the speed of the motor controlled. It is true that a resistor can also adjust the speed but that is not what we are dealing with. In our example the on time vs the off time is what sets the speed and the controller decides what to do based on the PWM signal that it receives (at least it does when it is working, no so much when it fails).
Summary you thinking about the Motor being Current Controlled is a good way to think about it but your assumption that the Voltage is constant isn't a reasonable assumption for this circuit.
The device that does the switching a Transistor (FET, IGBT or similar) does get hot due to the switching on and off and that is why you need the Heatsink.
I haven't seen any replies from Dr.JOE do you think he is going to fix it?
I saw a video that indicated that the Module was difficult to rotate. Has anyone done this?
Every single system on the car works from the voltage produced by the electrical system (battery, alternator). If the voltage is not 14vdc and the car is running it means the alternator is bad. No exceptions. If you have a theory that makes this statement wrong, I'm sure every physicist would like to hear about it.
