Reading the thread below related to the melted HVAC blower motor connector, moved me to post about changes to GM blower motor technology, that at least for GM pickup models was introduced in the new body style 2014 models.

It seems that the DC brushed electric motor has been around forever and for whatever reasons, GM engineers have moved to adopt brush less AC motor technology. We can debate why, but eliminating the annoying ticking of brushed motors at low speed is reason enough.

With sensitive electronics susceptible to EMF and HFO-1234yf refrigerant soon to be widely adopted as just a couple reasons worthy of consideration, I'm sure that there are other reasons we might think of other than keeping the engineers busy! VBG.

So, when a student brought an HVAC blower motor to class from a 2014-2015 something GM pickup truck that had been replaced due to submersion in water, we "Curious Georges" could not resist the temptation to take a look.

The traditional design "squirrel" cage or "hamster" wheel that was pressed on during manufacture, was removed for better viewing and the module cover on the back side removed to reveal the controls board and 3 phase connections. What remains is the AC motor. The stationary 3 phase windings can just be seen in this view, Blower Motor 1 along with the module heat sink. The control module and basic connections for a simple bench operational test are shown here. Control Side

Here Blower Control Logic is a "down and dirty" re-creation of the basic circuit using the bare minimum to operate the motor through a fused B+ jumper and B- to the main terminals of the module and connecting our trusty Kent-Moore signal generator Signal Generator to the control circuit to replicate HVAC control signal inputs to the blower motor logic module.

Increasing the duty cycle lowers the motor shaft RPM and conversely, decreasing duty cycle increases shaft RPM. The motor is almost silent and very powerful. With a strip of photo tachometer tape affixed, I seem to recall around 4000 RPM being measured.

Of course, with the change in technology from DC or AC, comes some revision in diagnostics. The AC motor does not allow for traditional "bench testing" through connection of power and ground to the older, most basic of DC blower motors.

Regards,

Martin from British Columbia

Files Referenced: