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Voltage divider circuit with integrated diode (AC blower resistor)
Replaced an AC blower motor, old one's commutator was well worn down to it's core.
Also pulled the AC blower resistor. Found a diode integrated into the circuit board.
Tested the diode using multimeters 'diode test mode':
1. ~0.6V in forward direction
2. ~0.9V in reverse direction
Diode allows current flow in reverse direction so assumed it was faulty. Purchased a second hand blower resistor & the diode on that one also allows current to flow in the reverse direction. The diode symbol printed on the circuit board (adjacent to the component) is that of a standard silicone diode.
With old resistor installed, fan speed control is okay.
My questions:
1. What is this diode used for? I'm assuming it's used as a shunt for back emf?
2. Why is this diode allowing current flow in reverse & still allowing proper control of blower speed?
Is it possible that this is a zener diode? In relation to question # 1, I'm assuming then that it's there to regulate voltage?
It sounds like it is in fact a zener diode. Without knowing the circuit design I can't say why they use it, but it is likely that it is used as a voltage regulator.
