Sam Brown

[Sam Brown]

Hi Brandon,

First off, let me address your two questions about the course material:

One:
It was explained that the refrigerant is compressed into the condensor coil would not this simply make the hot boiling gas coming from the evaporator a much hotter liquid? But if the object of the condensor is to make the refrigerant cooler, why does it have to go through this phase change which makes it even hotter? Is it due to volume concerns? Please explain. Thank you.

Remember that the whole point of the sealed system is to absorb heat from the refrigerator by the phase change from liquid to gas. In order to get the refrigerant in a state where it can boil from a liquid to a gas in its next go through the evaporator, it needs to be compressed. Higher pressure = higher boiling point. That’s the job of the compressor.

Now, compressing the refrigerant does make it hotter, but that’s why you have the condenser right after the compressor. The condenser allows a lot of that extra heat to radiate off the refrigerant. This cooling down, combined with the much higher pressure in the condenser compared to the evaporator, causes the refrigerant to change phase back from a vapor back to a liquid. Once it’s done this, it’s ready to exit the condenser, go through the capillary tube, and turn to gas all over again in the much lower pressure evaporator.

Two:
Does the damper exclusively allow a one way flow of air from the freezer to the fresh foods compartment? if so, how does it do this? from positive or negative pressure of a fan, or some mechanical means like in a check valve? Thank you for your time reading and for you responses.

The damper is for airflow from the freezer to the FF compartment. There is also a separate return duct, since otherwise the air pressure would prevent any air from moving from the freezer to the FF compartment. Normally, there doesn’t have to be a separate fan to push air through the damper — the evaporator fan does that.

As for your specific question about your aunt’s refrigerator, that would be a great question to post over at Appliantology. That’s our tech help forum that you have access to with your free MST Student membership. Start a new topic in the Appliance Repair Tech Help forum asking your question. That way, you can get both my advice and that of all the other talented techs at that site.

[Sam Brown]

Clarify where the points are from a supposed potential to the other side of the potential circuit. Otherwise points could mean points on the same side of the load.

Sometimes you do make a measurement between two locations in order to check if, for example, a switch is closed. It all depends on the kind of test you’re making.

When we talk about test “points”, we’re never referring to the pre-existing dots on the schematic. We’re always talking about chosen test points in the circuit — for example, I could call out test points as CN7 pin 1 to CN5 pin 3. As I said, sometimes those line up with the dots on the schematic, and sometimes they don’t. The dots are just indicating terminals, connectors, and tie points between wires.

Don’t get too hung up on the word “point”. Pay more attention to the specific designations, like “CN7 pin 1” mentioned above.

Again, is there a specific video or course unit in our material that you’re referring to? I’m happy to clarify, but it’s difficult to talk about these things as generalities.

[Sam Brown]

Sorry for the delay in getting back to you. To answer your question:

All infinite switches work in the fundamentally the same way. You have a bimetal that gets heated as current flows through the switch, and how often that bimetal actuates depends on the setting of the switch. In this way, all infinite switches are current-regulated devices.

As for swapping out an infinite switch, you would just need to make sure that they have comparable specs.

[Sam Brown]

Could you let me know exactly which video or bit of text you’re referring to? That will help me explain this.

But in general, if we refer to taking a measurement between two points, we’re referring to the points in the circuit where we would place our probes. Those measurement points often do line up with the dots on a schematic, since those dots often indicate connectors where measurements are convenient.

[Sam Brown]

In computer-controlled refrigerators, the thermistors tell the control board what temperature the compartments are. If a thermistor has gone out of spec to such an extent that it’s telling the control board that the compartments are already cold, then the control might decide not to run the evaporator fan or the compressor at all. To the board, the compartments feel like they’re at the correct temps already and don’t need any cooling.

Make sense?

[Sam Brown]

Slave systems are covered in module 1, unit 12 — the one on dual evaporator systems. Review that unit for more info on them, and let me know if any of it doesn’t make sense.

[Sam Brown]

Three-phase power output requires three outputs — one for each phase. So yes, three pins. You would simply hook up the tester to all three pins and test that way.

[Sam Brown]

Hi Shawn,

I see where the confusion is coming from — we’re not talking about the solenoid becoming literally flakey — as in bits of it flaking off. We’re using flakey in the non-literal sense, meaning that the solenoid has become unreliable and started to fail.

Because metal expands and shifts slightly when you heat it up, if there are any micro-breaks in the solenoid coil, they can cause the solenoid to operate correctly at first, and then go open after it’s begun to heat due to the current flowing through it. This is called failing under load. Heating the coils with a hair dryer simulates this and lets you quickly see if this is the issue you’re facing.

So the test in question would be to first energize the solenoid, then heat it up with the hair dryer and see if it goes electrically open.

[Sam Brown]

Hi Shawn,

Using the schematic, you would first identify the pin on the main control that outputs the PWM signal. Then, you would simply measure that with your meter with respect to a valid DC ground. Note DC ground, not AC ground. That’s all there is to taking a frequency measurement.

[Sam Brown]

How is this test conducted? the tool has three leads so I’m gathering that this would be hooked up to the MCU or the motor but not sure.

You would simply hook it up to the output of the MCU while it’s trying to run the motor. That way, the tester can see if the MCU is putting out a valid three-phase power supply.

[Sam Brown]

Can a data communication line transmit data back and forth or only in one direction?

Yes, it can transmit data signals in both directions! Sometimes you will see more than one data line connecting boards, but often you do only have one. But that does not necessarily mean that only one board is doing the talking. In fact, you almost always have two-way communication happening in multi-bard configurations.

[Sam Brown]

“Cold” is a relative term. Refrigerant that has left the evaporator coils and is on its way to the compressor is generally around room temperature. But you’re right in that it is relatively cooler compared to after it goes through the compressor. By the time the refrigerant leaves the compressor, it will have heated up significantly compared to before it entered the compressor.

[Sam Brown]

Dryer vent pressures don’t vary too much from brand to brand, so yes, the tester should work regardless of the brand.

[Sam Brown]

As shown in the diagram, L1 is being removed from the heater. We’re not talking about unplugging the entire appliance — just removing the L1 spade from the heating element.

The reason for doing this is to isolate L1 and L2 from each other in order. This is because, if both are connected to the heater, whichever line isn’t missing (in this case L1) will feed through the heater to the L2 side of the circuit, making it impossible to distinguish which is actually missing. However, once you have one of the lines disconnected, the lines are completely isolated from each other, so you can tell which one reads 120 volts wrt neutral (meaning that it’s present) and which one reads 0 volts wrt neutral (meaning that it’s missing).

Once you’ve identified which line isn’t making it to the heating element, that’s when you would proceed with your troubleshooting to find out why that line is missing. For example, it could be missing at the wall outlet, or there could be an open elsewhere in the circuit.

[Sam Brown]

Great question, Troy — the explanation in the Kleinert book is badly worded and confusing. That’s why we don’t recommend it as a textbook and only as a reference.

This image has a better explanation of what’s going on. This type of circuit configuration is called a voltage divider, and the CPU essentially acts as a voltmeter, with one “lead” connected to ground, and the other connected to the hot side of the thermistor. That’s how the CPU detects the voltage drop across the thermistor.

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