BCNR33 Blower Motor Resistor - Testing

[itsforandres]

hello!

does anyone have a schematic that shows how to test the blower motor resistor for the vac system? i believe the part# is 27761-15U00. I think the resistor is toast, but would like to be able to test it somehow before i embark on the journey to find a new one.

cheers!

27761-15U00

Edited May 23 by itsforandres
added tags

[dbm7]

G'day ... first up, I very much doubt that's a resistor network (as used also for this job), but the part# looks right. The description of 'power module assembly' looks to be nissanese for 'PWM driven, ground switched, DC motor speed controller'.... the circuit in the schematic kinda infers that's the case...

...with the transistor symbol appearing in the unit described here as 'Fan Control Amp(lifier)'....being driven by pin20 on the HVAC unit,  and a feedback signal on pin19 from the motor negative terminal for some reason (might be motor fault detection, maybe they detect commutator switching to determine motor revs as well, I dunno)... but if they are  counting commutator spikes, a bad segment (or really worn brushes) will throw a spanner in the works...

The motor itself will as said be brushed DC with segmented commutator, rated at 12VDC nominally ~ now-a-days I just unplug them, determine the positive wire, and hook them up to a variable power supply and find out how much current they draw, if they work etc etc ...you can also check for bad segments...ie; set the power supply up to feed 1volt @ 2amp max, then watch the wattage count as you slowly rotate the fan blower motor through a complete revolution ; any bad/dead segments will be clearly evident...some folks would just say determine the positive wire, and feed it battery voltage, and if fan spin, you've got a win...<grin>... well, at least that infers it should do something when plugged back in, and the HVAC unit commands it to run... and if it doesn't, you suspect the module, but you should check the PWM signal on pin20 is actually present, and if it is, blame the module ...

 

[GTSBoy]

^ This is all good advice.

I can imagine that there's some passive components in the HVAC controller that run that PWM output that could die, or suffer bad solder joints. It can be worth opening it up, taking a schmooze around looking for swollen electro caps, evidence of liquid escape anywhere, tracks that have been hot, lifted, cracked, etc.

A DMM might not be suitable for seeing if the PWM output is pulsing. Might be too fast and too low voltage for a DMM to keep up. An analogue voltmeter might give a better hope. I use a handheld oscilloscope (<$100 from Aliexpress if you want something cheap). A DMM might see the voltage across the motor flicker. Otherwise, as above.

If you can successfully see PWM action, then the control side should be good. If you can't see it with what you have, you might need to step up the instrumentation used, as above.

Beyond that, and dbm7's advice on testing the motor directly, you're down to looking for broken wires, corroded connector pins, etc.

[itsforandres]

@dbm7 and @GTSBoy thank you both very much! will give that a shot!

[dbm7]

Oops... I meant to include the connector  view...

BR/W - power from fuse

L/W - motor negative to fan control amp (and off to HVAC pin19)

OR/B - PWM signal (from HVAC pin20)

B --  ground

 

[itsforandres]

you, sir, are a prince. good on ya. 

 

Edited May 24 by itsforandres
goon instead of good!!

[itsforandres]

9 hours ago, dbm7 said:

Oops... I meant to include the connector  view...

BR/W - power from fuse

L/W - motor negative to fan control amp (and off to HVAC pin19)

OR/B - PWM signal (from HVAC pin20)

B --  ground