VARIABLE SPEED: Torque changes with ESP change = constant CFM.
CONSTANT TORQUE: Torque remains constant with ESP change = CFM drop with ESP increase.
PWM - Pulse width modulation: Low voltage that is sent from the PCB to the motor module.
RPM FEEDBACK: A calculation expressed in low voltage that is fed back to the board. This feedback indicates the motor is doing what it was told. Not all ECM have a feedback.
Serial Output: A method of communicating data; typically computers.
Slight "cogging" or rocking is inherent to all ECM motors: The motor is finding its location between stator and rotor and is determining its rotation.
"Rumbling" sound during startup and shutdown: System mechanical resonance (approximately 300-400 rpm) - three (3) permanent magnets (stators) cause the rotor to have a "rumble" during low RPMs.
"Fixes": Don't replace the motor! Isolate the sound: canvas duct connectors, rubber grommets, etc.
ECM motors should NOT bet tested UNLESS under LOAD.
Erratic motor behavior could occur without a load (static pressure) - this means leave the motor in the blower housing with the wheel attached.
Motor shaft turns, but not smoothly (with blower wheel disconnected)
Continuity of windings - they should be equal ohms.
Motor leads to the unpainted motor end plate.