[Harry Yarnell]

I've got a bunch of HVAC blower motors harvested from Norman's sitting on the shelf. I want to test them to see if they're any good.
The FSM shows a chopped ground signal on the grey control lead.
Applying + 12 volts to the red and blk leads, and grounding the grey, the blower will start to ramp up after a second or two; run at, I assume high speed for 5 seconds and shuts off.
Many seconds later, the cycle repeats.
Is this normal? I've only tested two so far in this manner.
Anybody ever tested these rascals?

 

[Submariner409]

Never fooled with one on the bench at 12V - but it sounds as if the straight 12V is tripping some sort of circuit breaker. Most of those are PWM speed-controlled.

 

[sefiro]

Try lower voltages, GM used a multi resistor for speed control. Resistor will drop voltage - and heat up thus being located in the air channel

 

[basscatt]

1993 and older used the simple resistor to control speed -
bench testing should be easy with a 12 volt source -

1994 and newer uses pulse width -
I don't think there is a simple way to bench test them -

 

[Harry Yarnell]

The late 80's, early 90's blower controls weren't resistors, but solid state (electronic) controllers. They were in the plenum.
The newer controllers (94-'02) were built into the motor. These are the ones in question here.
Prior to that, yes, they were resistors.
The term 'pulse width' is just a fancy term for chopped voltage.
The dash controller (late Caddys) for the blower, controls the ground side of the motor assy. It literally pulses, or chops the 12 volts to control speed.
Can't see why this can't be done on the bench.
Will play with this some more today and report.

 

[sefiro]

:banghead: too much early bourbon on Friday. . .


Oops, my bad, missed the pwm word.

(Started as a Electrical Engineering major, switched to computer science, tacked on finance, became a management consultant, and all I can read is people , thus a soccer ref, where we prove time and time again that we can't see or read)

Yes, PWM. Pulse width is technically a width of a certain voltage spike. Similar to an injector width ie gas flows at a certain pressure (voltage) and amount allowed through of the width of the opening.

(A resistor would slow a device down by limiting the amount of current , at a cost of heat and damage to the motor (leads to micro start/stop of the motor). The bled current via heat is considered a waste and draw on the battery and thus the alternator decreasing mpg. A resistor controlled device can be operated at a lower voltage, but at certain lowered voltage, will stop altogether giving a false fail)

The basic pwm mechanism uses a transistor (mofset). The transistor is basically a gated device. Current flows from one pin to another based on the signal current fed to the third pin. The signal current comes from a controller.
(Same principle in a led , a computer chip that integrates an emitter, a transistor and a controller)

And you are wondering, could I control it manually flip the switch quickly. Yes, but probably creating at best, a 90% speed.

In any case, if it comes on at 12v, great, it is working.

Like a resistor controlled device, a pwm controlled device, can operate at a lower voltage, but at too low a voltage, will stop and give false fail as well.

 

[Harry Yarnell]

I tested 4 motors on the shelf and 1 in a '96 Eldo.
Three leads go to this motor; red 12 volts, blk gnd, and grey control.
Grounding the grey lead made the motor run at full speed (from what I can tell). Ran like this for 10 seconds, then quit. Cycle could be repeated. They all did the same.
I suspect that if I could have tapped the grey lead at some fast rate, I could have produced a slower running motor, mimicking a pulse width control, but I didn't.
Time to dig out the scope and look at what the vehicle pulse rate is.

 

[gcwhitten]

Typically the PWM runs at a constant frequency with a variable duty cycle. The duty cycle is the fraction of time that the voltage is on. A DC motor will then respond to the average DC voltage. Here's a pretty good explanation, along with a PWM circuit you can build as a test circuit. The beauty of the PWM circuit is that it does not waste power. It also provides full voltage during the 'on' part of the cycle. This allows you to go much slower than a straight DC voltage would, since when it is 'on' it is all the way on. The down side is that you can generate some AC noise if the switches are fast.
https://www.electronics-tutorials.ws/blog/pulse-width-modulation.html

 

[Ranger]

My guess is that if you connect power and it runs, it's good.

 

[RomoRock3r]

Very curious about this topic.

The only way i've bench tested these was by plugging it into the car.

However there has been something i've been curious to test. These blower motors are just brushless motors. I think their main point of failure is the internal speed controller messing up. Supposedly the EMF from the coils cause the internal controller to mess up. However, The motor coils should still be good. This can also be verified with a multimeter.


I have a Computer Engineering background. I think its possible to bypass the internal fan controller and replace it with one of these hobby ones:

https://www.amazon.com/RC-Brushless-Electric-Controller-bullet/dp/B071GRSFBD

If you solder the 3 wires to the coils, the fan should spin with the external controller.

Basically all the large electronics inside the blower motor does the same thing as this little controller should do. In 20+ years, we've condensed all that large circuitry to the little ESC I controlled.


In addition. It may be possible to feed the PWM control signal from the car to this ESC. If not, with some engineering, someone could program a microcontroller to translate the car's blower signal to one compatible with the ESC.


If this is true, it may be possible to resurrect dead blowers by doing this. And to prevent other ones from blowing since its easy to insulate/replace the small ESC.