Cabin Blower stopped

The cabin air fan/blower suddenly stopped working in Dec. A 2004 with 119.6k miles.

With search I am aware of the issues with motor going bad, sticking, needing a push to get going and options to clean and tune up motor bushings. (correction, I meant brushes)

However my symptoms are a bit different. What I notice is that the fan will start on its own a few seconds after changing fan from off to a setting above med-high speed. It will run for several seconds (always the same length) then turn off again. Also giving it a push after it stops (or when it doesn't start in lower fan speed settings) doesn't get it going.

It doesn't seem to fit a 'sticktion' type cause.

I did order a replacement fan unit ($45) so it would arrive this Friday when I have time to work on it this weekend, but I am not yet sure that is the root of the issue. (I know I can test if it works with 12V input, but that needs to wait until this weekend) I also understand there is an electrical module built onto the fan assembly that converts the pulse output of the controller to an input the motor can use. I am hoping if the motor is not worn out, than perhaps that converter could have issues.

Any advice would be appreciated. I have a DVM, but not much else in the way of diagnostic tools.

 

Thanks.
That is my tentative plan, but thought if I could better diagnose before installing the fan and find it was not it, I could return it unopened.

 

Great advice, will try. The only thing I would not be sure of is if the controller automatically stops voltage if motor is drawing too much current or some other feedback.
Is the controller a home garage replaceable item?

Also what is the electronic item that is part of the motor assembly shown in this video at 1:50 (and happens to be the static frame for this video so you don't have to play it):

(I know it is not the controller, it is the 'electrical module' I was referring to in my first post)

You are correct, I did mean to write 'brushes' not 'bushing.' (The motor probably uses bearings not bushings anyway)

 

I've located in my Prius the small grey box that is the blower motor controller (87165)

CONTROL, BLOWER MOTOR. HEATING & AIR CONDITIONING - COOLER UNIT (PRIUS (NHW20)). TOYOTA PRIUS 1500CC 16VALVE DOHC EFI (2004 - 2009) # 8716547020


I've checked its output (that feeds the motor, terminals M in schematic above) with same results as the speed of the fan indicated:

When I switch fan from OFF to any speed setting 1-5 (where LO=1 M =4, HI=7) there is an initial voltage pulse of 5-8VAC that I an see on DVM tapering off quickly back to 0. This resulted in no movement of the motor.
When I switch fan from OFF to speed setting 6 or 7 there is that same initial voltage 'pulse' of up to ~8V. Then ~2sec later there is a pulse of >11VAC which holds for perhaps 1/2sec and then also tapers down to 0. This resulted in motor turning of briefly after an initial pause.

Note that when I don't press OFF between speed settings change when I switch between any speed 1-5 there is no change to the voltage (0 volts), but if I switch from any 0-5 setting to 6 or 7 there is an pulse of nearly 12VAC which quickly tapers to 0.

So this points to the fan motor not being the problem, as the problem is at the output of the blower motor controller, which is controlled by the air conditioner amplifier (88650)

AMPLIFIER ASSY, AIR CONDITIONER. SWITCH & RELAY (PRIUS (NHW20)). TOYOTA PRIUS 1500CC 16VALVE DOHC EFI (2004 - 2006) # 8865047050


How can I check if inputs to blower motor controller are correct - can it be done with only DVM and no oscilloscope?

 

I'm not getting much V reading across pin S1 and GND.

This is steady state result reading VDC:
o=0.00 (fan=OFF)
1=.0.13
2=0.11
3=0.09
4=0.07 (fan=MED)
5=0.05
6=0.02
7=-0.01 (fan=HI)
When fan is turned on from OFF to any setting it goes to 0.11 then drops to steady state value above.

(When reading VAC:
Fan settings 1-4 from OFF goes to .10 and holds there.
At 5 is goes to .10 then drops to .08
At 6 is goes to .10 then drops to .o4
At 7 it goes to .10 then drops to 0.00 V after a bit.)

I do get ~12VDC across both GND and S1 and across GNG and +B (? cant read well on above schematic) but only when fan is not set to OFF.

 

I found an oscilloscope and was able to determine that the waveform from the output of the harness that inputs to the blower controller (BMC) S1 terminal is peaking at 200mV - I can see it go from a narrow duty cycle to wide as I select from LO thru almost-HI but the waveform is not stable in higher fan settings where the voltage also varies from start to end of 'square' wave -. Setting HI result in no waveform.

According to this (last page), the waveform peak should be ~11V, not 200mV.
http://priuschat.com/attachments/blower-motor-circuit-pdf.33086/

Unless I am measuring wrong (does AC ECU need to be connected to BMC for the output of AC ECU to measure correctly?), it seems it may be the AC Controller is the issue or the harness that connects from AC Controller to the blower motor controller.

 

n/a

 

That is why I asked the question because I also saw that instruction on p.6. I could tap into the B+ line by cutting a bit of insulation so I can read it while it is fully connected and use any body metal as GND.

I have not located the A/C ECU yet, it is hidden behind the lower center panel, not sure how to get that off (I have not tried yet)

I can check the resistance between terminal S1 on the BMC to GND

 

It measures 6.4k ohm

(plug removed, checked resistance on BMC unit between GND terminal (where white wire with black stripe on the plug side connects) and S1 terminal on the BMC unit (where the thinner white wire in middle connects to on the plug side)

 

OK, so I did this and the results are better. So I suspect that the BMC does need to be connected to the A/C ECU for correct output.

This is what I got (0=OFF, 7=HI) DVM reading steady state (all settings from OFF first read 3.1V for a moment before switching to steady state)
1: 3.5V
2: 3.0V
3: 2.5V
4: 2.0V
5: 1.5V
6: 1.oV
7: 0.2V

I looked at the waveforms: LO fan settings have larger duty cycle than higher thru setting 6. Fan speed 7=HI looks flatline. 1 thru 6 have a 5V range from bottom to top of wave consistently.

This may be positive news for me as fixing/replacing BMC is easier and lower cost than the A/C ECU.