Sam Brown

[Sam Brown]

For the primary valve, which cycle is being clipped off depends on which other valve is being energized at the same time. As we established, if the dispenser valve (the top one) is being energized, it gets full line voltage because there’s no diode in series with it. But the primary valve will only get the positive half cycle because of the orientation of the diode.

The situation is similar with the bottom valve: the ice maker fill valve. This valve gets the full voltage because there’s no diode in series with it, but when it’s energized, the primary valve gets the negative half cycle because of the orientation of its diode.

[Sam Brown]

In that part of the video, Scott is talking about the cathode facing the load just as a way to clearly state which end of the diode is the cathode. Electrically, it doesn’t matter which end of the diode is facing the load. What matters is which end is facing Line and which is facing Neutral. And even that only really matters if you have multiple diodes involved, and you want them clipping off different half cycles.

For example, if you go back to the water valve diodes we were originally talking about, the top diode clips off the negative half cycle, as we already established. But the bottom diode clips off the positive half cycle, since it’s oriented the opposite way of the top diode. What matters is the orientation relative to the two legs of the power supply, not relative to the load.

[Sam Brown]

Fortunately, you do not need to dig far into the flow chart to find what you need to do this test. The very first step gives you the pins, and it calls them out as the “supply voltage” to the DSI. That’s what we’re looking for.

[Sam Brown]

Hi Denis,

Sorry that I missed your follow-up question. Let me see if I can further elaborate.

To quote what you wrote:

We are both talking about actual current flow, with the flat end of the triangle (the anode) pointed toward the positive charge, and the pointed end of the triangle with the bar attached to it (the cathode) pointed towards the negative charge.

Good that you clarified we’re both talking about actual current flow — that is, the movement of electrons.

I want to clarify too what exactly we mean by a positive vs. negative half cycle. We’re referring to the polarity of Line during that half of the AC cycle. The polarity of Line is what determines the polarity of the half cycle.

So, in the positive half cycle, Line is positively charged, and Neutral is therefore relatively more negative. This means that the negatively charged electrons will be moving from Neutral to Line, since they’re repelled from the negative charge and attracted to the positive charge.

Now, for our circuit in question: we’re talking about the upper diode. Line is attached to the anode, while Neutral is attached to the cathode. During the positive half cycle, Line is positive, so you have a positive charge on the anode, and therefore a negative charge on the cathode.

Here’s the definition of what it means to be forward biased, taken right from the unit:

A diode is said to be “forward biased” when the voltage on the anode (unbanded end) is more positive than at the cathode (banded end). In this case, electrons will flow from the cathode to the anode and out into the circuit.

So in the positive half cycle, electrons are moving. That means that it’s the negative half cycle when electrons aren’t moving. In other words, the negative half cycle is what gets blocked by the diode.

[Sam Brown]

Hi Denis,

You’ve got your anodes and cathodes reversed there — a diode is forward biased when there is a positive charge on the anode and a negative charge on the cathode.

With the example that we’re looking at around 9:02 of the video, let’s imagine the circuit during the moment in time when Line is positively charged. With the orientation of the diode, the flat end of the triangle (the anode) is pointed toward the positive charge, while the pointy end of the triangle with the bar attached to it (the cathode) is negatively charged. This means that the diode is forward biased, and current will flow.

If current flows only during the positive half cycle, then that means the negative half is the one getting clipped off.

Make sense?

[Sam Brown]

Hey David, you’re correct that that’s the operating principle of relays, and that’s a good summary of how they work, but what Nicholas is pointing out is the circuitry of the working voltage, not the control voltage.

And Nicholas, you are right that the way the schematic draws these relays is a bit confusing. Without looking at the relay’s physical construction, I would assume that the way L1 appears to tag off and then immediately come back to both the Bake 1 and Bake 2 relays is just showing the relays’ internal circuitry. For whatever reason, they draw it as if that line leaves the relay, but it probably just remains inside the casing of the relay.

It’s also possible that Line does actually leave the relay, travel through a trace on the relay board, and then return to another terminal on the relay. Why would they manufacture it that way? Not sure, but electrically, either configuration would function identically.

The point of course is that in one position, each Bake relay sends Line voltage to the corresponding bake element, and in the other position it sends Line voltage to the corresponding convection relay.

Let me know if any of that doesn’t make sense.

[Sam Brown]

Hi Denis,

You should be able to download that manual here at Appliantology: Click here

Make sure that you’re logged into your Appliantology account, otherwise the download won’t work.

[Sam Brown]

Could you tell me the differences between a temp sensor, thermostat, and a oven sensor? I think I understand that they all measure temperature but I’m guessing they measure the temperature in different ways?

This will be covered in much more detail later in the course, but I can give you a brief overview now.

“Temperature sensor” is a general term for a device that allows a control board to measure temperature. This will usually be either a thermistor or an RTD. Those are two different technologies that have the same property: their resistance changes in response to temperature. The control can measure that change in resistance and use that to detect the temperature of the sensor. An “oven sensor” would be an RTD, since that’s the type of temperature sensor usually used in ovens.

“Thermostat” is another relatively non-specific term, but it often refers to a temperature-controlled switch, like the kind you often find in dryer heater circuits. It is a switch that actuates (either opens or closes) in response to temperature.

[Sam Brown]

1 time a gas range wasnt lighting, (or staying lit, cant remember exactly) but after “ohming everything out” , everything tested good, and i was at a loss… it ended up being ‘bad’ coils.. that ohmed out good, but under load? was not good…. so my question is, what should i have done differently ?

Volts and amps tests would be the name of the game here. If you have voltage supplied to the coils, but the amps go away during run, then you know that they’re going open under load.

Similar thing with the fan — you needed to make sure it was getting a proper voltage supply, and then see if you had any amps.

[Sam Brown]

That situation is a little tricky, because you need to be really, really sure that you’re operating the diagnostic mode correctly. This becomes especially confounding when you have badly written directions, which happens sometimes. But yes, if you are sure that you’re operating the diagnostic mode correctly, and the diagnostic mode either isn’t working at all or isn’t working as it should, then you have a bad board.

[Sam Brown]

Unit 2 – the fan delay bypass test plug – is this strictly for placing a jumper wire to bypass the defrost terminator to test the evap. fan functioning? the defrost terminator – this is a bimetal that opens when warm, so the idea would be to not need that to be cold/closed for the fan to run?

Yes, it lets you test the evaporator fan regardless of the state of the terminator. It also lets you do the same for the defrost heater.

Are these for testing continuity of the bimetal when cold (closed) and/or jumping the bimetal to see if the defrost heater is functioning when the defrost timer is energizing it?

Yes, those terminals can be used for both of those purposes. You can either use them to place a jumper, or you can use them as test points for your meter. However, you could not use those terminal to test the defrost heater directly, since they only give you access to one side of the load.

[Sam Brown]

1. I understand that when draining, some water still needs to be left undrained in order to prevent seals from drying out.

So, when doing this, how does the dishwasher know when to stop the drain pump from draining, in order to ensure it doesn’t drain all the water?

The drain hose of a dishwasher is installed with a rise, such that the drain pump cannot pump all of the water out of the dishwasher. So no matter how long the drain pump runs, there will still be some water left in the sump.

2. My understanding is that in a dishwasher, the water needs to be hot, but it shouldn’t be overly hot because that will increase the amount of mineral deposits coming out of the water, causing extra mineral buildup. I also understand that the dishwasher’s heating element is there to heat the water to make sure it’s hot enough.

So I’m wondering if the dishwasher has a way to “know” whether the heating element should or should not be used (like for example a temperature sensor), in order to both ensure the water is hot enough and to prevent the water from getting too hot?

Most dishwashers have a thermistor to sense the water temperature, so yes, they can tell how much heating is requried.

[Sam Brown]

How do you create the condition that closes certain contacts?

You simply start a cycle and wait for the part of the cycle when that load is run. For the drain pump, that’s pretty easy — it runs right at the beginning of the cycle. So if you want to test that the drain pump is getting a good voltage supply, you would simply start a cycle and then measure from A1 to A9 — those are your EEPs for the drain pump at the timer. If you have 120 VAC and the drain pump isn’t running, then you’ve found a failed drain pump.

Let me know if you need more clarification.

[Sam Brown]

You’ve got the principle of it — let me just explain briefly how it works.

In the element’s circuit is a bimetal — a thermally controlled switch. Once the bimetal gets hot enough due to the element’s heating, the bimetal will open, shutting off the element until it cools off enough for the bimetal to close again.

The knob that controls the element puts physical pressure on the bimetal depending on its setting. The higher the heat setting of the knob, the more pressure exerted on the bimetal, and so the hotter it has to get before it will open the circuit.

That’s it in a nutshell, but if you want to understand this stuff in depth, that’s what the Oven and Range course is for.

[Sam Brown]

Hi Juan, sorry for the delay in getting back to you on this one.

You’ve got a really good handle on the refrigerant cycle! Your description all the way up to when the refrigerant enters the evaporator is spot on. Here’s the part of your understanding that needs some tweaking:

-The liquid moves from out of condenser into the evaporator. I believe somewhere along the way here, the liquid is decompressed (or in other words, expanded) which makes it get very cold (around -20 F I think?) before going into the evaporator. This liquid is now low-pressure I think, due to this decompression.

-liquid goes into the evaporator coils. the warmest air in the fridge is propelled by the evaporator fan through the evaporator coils

The key concept that’s missing in this description is how the phase change of the refrigerant works. When matter changes from liquid to gas, it absorbs heat energy to make this phase change. And crucially, even though the liquid refrigerant is absorbing heat to change into a gas, its temperature does not increase during this process. In other words, once that refrigerant reaches its boiling point, its temperature does not increase until it has completely changed phase to a gas, even though it absorbs heat to do this.

That’s kind of a wild concept, but it’s really how refrigerators work. We cover it much more in depth in the Refrigeration course, as Susan mentioned.

To your other point of confusion about how the pressure changes: this is accomplished simply by changing the size of the tubing the refrigerant is being pushed through. Leading up to the evaporator, the refrigerant has to go through a very narrow capillary tube. At the end of the capillary, the evaporator tube is much wider, which drastically lowers the pressure of the refrigerant. And a lower pressure = a lower boiling point, hence why the refrigerant starts to absorb heat energy to change phase to a gas.

Hopefully that makes sense as a brief summary. Again, if you really want to dig into this, that’s what the Refrigeration course is for.

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