Susan Brown

[Susan Brown]

My way: I open up freezer door, not hearing the evap fan motor, i close door, put ear against fridge to listen for any humming. When i dont hear any humming, i tap on cold control, and fridge kicks to life. First system i checked was the temperature control system

No- the first systems you checked were
1. the air distribution system (“not hearing the evap fan motor”)
2. the refrigeration system (“put ear against fridge to listen for any humming”)

THEN you checked the control system because you didn’t hear any humming. If you had heard the compressor running, you would have known to investigate the refrigeration system further.

You checked the compressor before the controls, which is exactly what we teach.

BTW – it is fine to note whether or not the evap fan is running while you are shooting the compartment temperatures to verify the complaint, but it is a very weak piece of information – you can’t really do anything diagnostically with that at this point if both compartments are indeed warm.

Remember, we’re teaching a troubleshooting system – a way of organizing our thinking and approach to troubleshooting all types of refrigerators – split-phase, BLDC, linear compressors, as well as single and dual-evap, with all kinds of control schemes. Of course techs will develop a few additional techniques or modifications based on particular models as they gain experience. For example, you’ll know that certain types of compressors will be impossible to hear by putting your ear against the fridge (e.g., BLDC, linear). But those are just layers that you add on top of a foundation of solid, logical thinking.

[Susan Brown]

No problem! It’s easy to hide answers, and I like students to see that others are using the Forums to get personalized help. Some students avoid asking questions for some reason, even though they obviously need to!

[Susan Brown]

Hi Nate – that is correct! I’m going to hide the answer, FYI, so we’re not giving away too much to other students.

[Susan Brown]

What I mean is that checking to see if the compressor is running, doesnt tell me if it SHOULD be running.

If both compartments are warm, then of course the compressor should be running! 🙂

Listening for evap fan noise is sometimes a good move but not diagnostically conclusive in the case where both compartments are warm.

The only diagnostically conclusive move at this point is to determine if the compressor is running or not. This also half splits the problem between the compressor and the other three systems.

We’re just talking about listening, depending on the type of compressor. Or, you may need to roll out the fridge and get a closer look/feel.

We teach a logical approach to troubleshooting that follows a carefully thought out rationale to maximize diagnostic information with minimal disassembly. But, are there other ways to get to the correct conclusion? Of course, but they won’t be as efficient. We like to do more work with our brains and less with our hands!

BTW – I encourage you to be more specific in your terminology. Saying that the “refrigerator should be running” is not precise. The refrigerator is the entire box with 4 systems.

[Susan Brown]

Hi Nate – I’m going to email you about this.

[Susan Brown]

Hi Scott,

In general, you want to choose the system you troubleshoot first based on both the symptoms that are presenting and the easiest things to check (minimal disassembly). For example, if both compartments are warm, one of the first things you want to know is if the compressor is running. Because if it is, then you know the control system is telling it to run, but it is failing to cool and you would then examine the compressor/sealed system further.

I disagree, because you need to know if the refrigerator is running first in order to know if the compressor should be running.

What do you mean by “you need to know if the refrigerator is running” – which system are you referring to? What do you think should be checked first?

[Susan Brown]

Yes, those are the simplest definitions of those conditions that we need to know as appliance techs. You’re welcome! I’m always glad when students as clarifying questions like this.

[Susan Brown]

Yes, that’s basically it!

A shunt will bypass one or more loads, but there will always be at least one load in the circuit that is not shunted. Shunts are usually by design, but you could have an accidental shunt, where a load is unintentionally bypassed by some kind of fault condition, but there’s still an active load somewhere else in the circuit.

A short is a fault condition where ALL loads in a circuit are bypassed somehow.

[Susan Brown]

No problem! I just reset you.

[Susan Brown]

Ah! It’s got different settings than other exams, so I will have to reset it manually so you can retake it. Are you ready now?

[Susan Brown]

No apologizes necessary! Sometimes we have to look at things from various directions in order to get it to finally click in. Learning is a process. When I was helping Scott put this course together, you should have heard all the different questions I asked him so that I could figure this stuff out (made for exciting dinner conversations!)

Does this mean that if we have parallel circuits, and one of the paths does not have a load – that electrons will not move through all the paths? Would the one path without a load act as a shunt?

Yes. That’s what a shunt is – a path with no load that is parallel to one or more paths that do have loads. Circuits are often designed with shunts that have a switch in them in order to control another load. If the switch is closed, then the shunt will prevent current going through a load. Then if the switch opens, the current will instead go through the load(s).

Let me know if you have any further questions about that.

Now I’ll ask you one more thing – do you know the difference between a shunt and a short?

[Susan Brown]

Hi James,

I’ve reset you. If you should need another reset in the future, please use our Quiz & Exam Reset Request form (under “contact us” in the main menu). That will get your request to the proper person more quickly!

https://my.mastersamuraitech.com/quiz-exam-reset-request/

[Susan Brown]

Hi Nate,

Great question! Yeah, that “path of least resistance” saying is problematic. It’s sort of correct, but not completely, which is why we don’t like it.

First of all:

And how does electricity know to follow the path of the shunt?

Remember that electrons don’t “know” anything. Fortunately for us, they don’t do independent thinking, and therefore follow consistent and predictable patterns 😉

Electrons will move in response to the presence of voltage if they have a complete circuit. When there are multiple paths available (parallel circuits), and if each path has a load in it, then electrons will move through all of those paths.

If the resistances are different in each of those parallel paths, then that will affect how much current each path gets. Lower resistance will result in higher current flow. (I = E/R, so as R gets smaller, I gets larger), and vice versa. But they’ll all have some flow, even if one of the resistances is significantly higher than the others. (This is why the “path of least resistance” saying is problematic – it sounds like all the current will flow in the path with lower resistance.)

A shunt is a pathway with zero resistance. In this circumstance, ALL of the electrons will go through this path, none will go through the circuits with loads, and we call it a shunt.

Does that help?

[Susan Brown]

Hi Robert,

He is correct that the shunt bypasses loads D, E, and F. When the electrons come to that tie point on either side of the parallel loads, they can either go through one of the loads or go through the shunt wire – they are all tied together. If electrons have a route that they can take with no load in it, then they’ll take it 100% of the time!

[Susan Brown]

70 ohms is the total resistance.

What is your second calculation? You gave the answer in “ohms”. Is that what you meant?

With calculations like this, it is good to write out the units and what you are trying to calculate, so that you can keep everything straight.

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