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Appliance Repair Tech Tips

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The Schematic or the Written Directions -- Which Should You Trust?


Son of Samurai

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We techs rely on accurate technical documentation to do our jobs. You can't make a troubleshooting plan or make meaningful electrical measurements without a good schematic. But what do you do when your technical info contradicts itself?

Let's take a look at this Whirlpool refrigerator, specifically focusing on the evaporator fan. Here it is on the schematic, marked up for your viewing pleasure:

Screen_Shot_2021-06-06_at_10_36_02_AM.png

Looks like a standard 120 VAC fan motor. But now, let's take a look at some of the written directions elsewhere in this same tech sheet. These are the instructions for the evaporator fan's step in diagnostic mode.

image.png.74511ff3ac102c8efee260a7b28d3d23.png

A two-speed fan? That runs on DC power? That's not what we saw on the schematic...

We need a second opinion. Fortunately, we've also got some specs in this same tech sheet, and these agree with the schematic. Not only do they show that this is a 120 VAC fan motor (yes, yes, I know it says 115, but we use nominal 120 nowadays), but they also show only a single speed.

Screen_Shot_2021-06-06_at_10_33_04_AM.png

If this truly were a variable speed fan, they wouldn't give us a single RPM spec like this. We're not dealing with a two-speed DC fan motor here -- just a standard 120 VAC one.

Moral of the story: If you see a conflict between the schematic and the written directions, go with the schematic. Now, don't take this as gospel, but as a rule of thumb. Schematics can have errors, too -- I've written blog posts about them -- but generally speaking, manufacturers make fewer errors when drafting their schematics compared to writing out directions.

Written directions like the ones that gave us the bad spec above are what we technical-minded folks like to call dummy directions. Always take them with a grain of salt, and if they conflict with the schematic, odds are they're flat-out wrong. This does not mean that you don't bother to read through them -- it just means that you use your discernment and technical knowledge when you do so.

Want to learn how to read technical docs with confidence and attain complete troubleshooting mastery? Click here to check out the online Core appliance repair training course over at the Master Samurai Tech Academy.

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  • Team Samurai
Samurai Appliance Repair Man

Posted

Much practical wisdom in this post! In cases like this where there's a discrepancy between what's shown in the schematic and the spec block of the tech sheet and what's written in the service test descriptions, another thing you can do is look up the part(s) in question (evap fan or condenser fan) at an online parts site and read the spec label on the motor itself. 

For example, the model in question for this post is Kitchenaid KBFS22EWMS3. Plug that into an online parts site like RepairClinic or Appliance Parts Pros (two sites that have good photos of many parts), and look at a photo for the evap fan motor and condenser fan motor. You'll see this picture for the evap fan motor:

Whirlpool_W11024089_Evaporator_Motor_-_AppliancePartsPros_com.png

Any tech who's been in the trade for a just a few months shouldn't even need to see the spec label on the motor to know what kind of motor this is just by sight: it's a standard shaded pole motor. Shaded pole motors are single-speed AC motors. Always and everywhere. 

The condenser fan motor can be a little more tricky. Let's take a look: 

Refrigerator_Condenser_Fan_Motor_-_W11387394___Fast_Shipping_-_Repair_Clinic.png

Oh my, this is confusing-- its doesn't look like a shaded pole motor at all. Instead, it looks like it could actually be a 4-wire BLDC motor. How can we tell for sure? Check the specs on the motor! Here's a picture of the spec label on this motor: 

WHIW11387394-K-2T_jpg_1_150×1_100_pixels.png

And there it is bigger than life: the AC power supply spec is printed right on the motor label. No BLDC, variable speed motor here! 

This is just another easy and practical way to clear up conflicts between the schematic and the technical writeup on tech sheets.

Go ye forth and conquer! 

  • Like 4
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Thank you!

The only trouble I have is determine which pin supplies the Neutral to the fan. There are two possible variations of WH/BK wires on CN2 pins 4 and 5. How do you chose, or either one will do?

image.thumb.png.e84753d93a7a927868e7085bf907de2e.png

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  • Team Samurai
Samurai Appliance Repair Man

Posted

Anytime you see redundant wires like this in the power supply to a load, these are usually sensing lines that the board uses to determine if the load is getting a valid power supply in a complete circuit.

In this case, we have a sensing line in the Neutral side of the motor’s power supply. The board uses the extra line to sense the presence of Neutral.

More info on sensing lines in this post: 

 

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3 hours ago, Samurai Appliance Repair Man said:

Anytime you see redundant wires like this in the power supply to a load, these are usually sensing lines that the board uses to determine if the load is getting a valid power supply in a complete circuit.

In this case, we have a sensing line in the Neutral side of the motor’s power supply. The board uses the extra line to sense the presence of Neutral.

So one of the redundant wires is the Sensing wire. But in this particular case, both pins 4 and 5 run un-switched wires to the load. Since it's not marked on the schematic, either one of them could potentially be a Sensing or a Neutral wire. So if I need to check the Evap fan, I'll use pins 8 and 5... but pins 8 to 4 should give me the same result, right?

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  • Team Samurai
Samurai Appliance Repair Man

Posted

17 hours ago, Slav said:

But in this particular case, both pins 4 and 5 run un-switched wires to the load

This is not necessarily a true statement. The board itself is functioning as the switch to the load.

Let’s suppose that the board switches Neutral to the motor. That switching could happen on pin 4 or pin 5. We don’t know based on the paucity of information offered to us by Whirlpool. But it doesn’t matter because both points are EEPs— they look identical to electrons. So when either of them closes and supplies Neutral to the load, the other point looks the same to electrons and, more importantly, to our meter. Given this information then... 

17 hours ago, Slav said:

So if I need to check the Evap fan, I'll use pins 8 and 5... but pins 8 to 4 should give me the same result, right?

Da tovarish! Or, as we say at Appliantology, “Correctilia.”  

  • Like 2
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46 minutes ago, Samurai Appliance Repair Man said:

This is not necessarily a true statement. The board itself is functioning as the switch to the load.

Let’s suppose that the board switches Neutral to the motor. That switching could happen on pin 4 or pin 5. We don’t know based on the paucity of information offered to us by Whirlpool. But it doesn’t matter because both points are EEPs— they look identical to electrons. So when either of them closes and supplies Neutral to the load, the other point looks to the same to electrons and, more importantly, to our meter. Given this information then... 

Da tovarish! Or, as we say at Appliantology, “Correctilia.”  

Spasibo!

Learning appliances is fun, but learning new words is priceless :)

  • Like 2
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Was this an actual call? Like did you test the fan in the service directions? What did the refrigerator do?

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  • Team Samurai
Son of Samurai

Posted

Just now, vallen513 said:

Was this an actual call? Like did you test the fan in the service directions? What did the refrigerator do?

This was a piece of a war story from one of the techs here at Appliantology. I don't believe he ever said how that step of the test behaved, but he did confirm that it was a simple 120 VAC fan motor.

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5 minutes ago, vallen513 said:

Was this an actual call?

Here is the thread:

 

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