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The start and run windings are described as changing from being in parallel to in series.
I would need the context in order to address this properly. Do you know where exactly in the course material it states this?
I’m assuming the smaller elements are supplied with 120 VAC and the bigger elements are supplied with 240 VAC?
Usually, electric heating elements have a 240 VAC power supply, whether they’re big or small. You might see a 120 VAC electric heater in something like a warming element on a stovetop, though.
1. For this example, the customer states there is only 1 condenser. Don’t rely on the customer. But is this accurate? It wasn’t addressed as inaccurate so I didn’t know if I missed something. I would think not accurate but I only see 1 condenser fan on schematic and am unsure?
Could you please tell me which timestamp in which video you’re referring to here?
2. The 4th video – about 21:50 – disconnect the P2 connector and then measure for the data signal and you get the 3 VDC we were looking for. I do not understand. It is disconnected, why do we measure anything? I’m sorry, I did not understand this process. I understand we are trying to isolate the fans to determine which is loading down the system. I think I understand what loading down is and plan to reference the additional video. But I missed something.
What we mean by this is that you disconnect from the board the connector for the load that you suspect is loading down the system. Then, you put your meter leads on the pins that that connector was plugged into on the board. If that load was the culprit, you should be able to measure the DC voltage at the board that was previously missing.
1. In video 2, around 15 minutes in, failure modes for TDM valves are discussed. I understand the valves, differences, paths refrigerant can take, etc. I’m a little confused on the testing. “for testing – set fridge temp warmer than actual temp (so that 3 way valve should route refrigerant to freezer only, if any), monitor the defrost sensors (at the board) to see if voltage drops.” These defrost sensors are temperature sensors at the evaporator that let the board know when defrost is needed, correct? I’m looking for voltage drop – is there a chart I compare this to, like for thermistors that monitor the compartment temperatures?
Yes, the service manual or tech sheet should (if the folks putting them together did their job) have a table of thermistor voltage drops and/or resistances, showing which value corresponds to which temperature.
2. The finger test – is it ever the case that the valve body just happens to be in that position per MICOM instructions when you cut the power? So when you plug it back in to cycle it back to home, you feel nothing and then assume the 3 way valve body is broken?
The 3-way valve only moves to the home position briefly at the end of a defrost cycle and during the self test when the unit is powered on. So you should always feel the valve moving during the power on self test.
3. For general residential refrigerator – is a broken 3 way valve and sealed system repair something you usually do or get a new fridge?
Whether or not you do a sealed system repair depends entirely on the model you’re working on. For lower end refrigerators where the cost of a sealed system repair is about the same as the cost of a new unit? Most likely not. But for higher end models, built-in units, etc., sealed system repairs are absolutely worth doing.
Let me know if I properly answered all your questions. If not, please post the timestamps of the videos you’re referencing so that I can give you more detailed responses.
1. During the troubleshoot instructions, under step 3. We disconnect the AC power supply to the inverter board and connect the amp meter to one of the power supply lines. First: are we disconnecting and then reconnecting to make the inverter try to run the compressor (like a reset type thing?) or what is the reason. Second: when you say connect amp meter around one of the wires supplying 120VAC (doesn’t matter which one) – do you mean the L1 wire or neutral wire (as the two options)?
You’re on the right track — power is cycled to get the inverter to start the compressor while you’re checking amps. Upon rebooting, the control will perform a self-test, during which it tries to run the compressor momentarily. If it finds that the compressor does not run, then it is usually programmed to stop trying until power is cycled again.
As for where to take the reading, it doesn’t matter which wire you check amps on — current is the same at every point in a series circuit.
2. At 3:29 of the video, he states that the output from the inverter to the compressor is VDC that will vary in frequency. This has tripped me up before so I wanted to make sure – this is correct? And then the switches, which are at the compressor, effectively commutate this VDC into an AC like voltage? And the circuit on the other side of the compressor continues back to the inverter.
It gets into technicalities and semantics a little bit, but the output from the inverter is *commutated* DC, which is technically a type of AC. The switches that perform this commutation are electronic switches in the inverter.
Let me know if anything is still unclear.
Why wouldn’t we read 120 if we didn’t have a valid neutral?
All voltage measurements are a comparison between two points. You put one lead on the place where you want to measure the voltage, and the other lead on a reference point that you know has 0 volts of potential — that’s Neutral. If your reference point is not connected to Neutral, then your measurement is undefined.
An undefined voltage measurement with a loading meter will read 0 volts. That’s because, when you’re missing Neutral, there is not a valid circuit, and so there’s no voltage drop across your meter.
If you’re using a non-loading meter, like the VAC function of your multimeter, things can be a bit more fuzzy. You might still read 0 volts, but you could also read some ghost voltage. This is why we recommend that you always use a loading meter for AC voltage measurements.
Either way, you would not read a solid 120 VAC unless you have a valid Neutral.
Would this mean that the door switch is for sure good? You would still measure 0 across the push to start even if neutral was open because of the door switch, right?
The 0 VAC reading by itself would be ambiguous, but we did a reading before that with the switch open and got 120 VAC. We would not have gotten this reading if there were not a valid neutral. That’s how we know that we are getting a valid neutral through the door switch.
Service manual clearly stated all voltages supplied from main board. This model has 3 different Voltages, supply, feedback and signal. Was getting supply voltage and signal but no feedback.
The feedback signal is definitely not an output from the board. It is a signal generated by the motor’s Hall sensor when the rotor spins, which is then sent back to the board. So it is an input to the board, not an output.
If the manual says or implies that it is an output, then that is an error in the manual. Errors like that are not uncommon, especially in manuals that have been translated, like LG’s.
Hopefully that clears it up! This was a great question, and in the future, questions about problems you encounter on the job are usually best posted at Appliantology. That way, you can get help not just from us, but from a bunch of other experienced techs, too.
I guess with a compressor, the line voltage is supplied separately to the inverter. It is using the line voltage (AC) to put out the appropriate DC power, which the switches are commutating into effectively AC power, right? So it goes AC input from line, changed to DC output that board is actually creating but that output is effectively changed back to a 3 phase AC voltage via the switches?
Great summary! This is all correct.
For example, this BLDC compressor motor shown in the second video of 1.13 at about 15:12. The return circuit for the BLDC motor connects to the inverter. This portion is an AC circuit? That would require my meter to be in AC and requires the neutral that is connected to the inverter to be a complete circuit?
You can’t really make sense of the output of the inverter with a standard meter because it’s 3-phase power and the frequency varies widely from your standard 60 Hz power. But yes, the inverter takes a 120 VAC power supply (which consists of both Line and Neutral — you need two legs to make a power supply), rectifies that into high voltage DC power, and then commutates that into what is effectively 3-phase AC power with varying frequency.
And yes, separately from all that, the inverter also converts its 120 VAC input to a low voltage DC power supply for its internal logic.
1. In a slave system, how is the freezer compartment evaporator coil supplied with liquid refrigerant (rather than vapor) after the refrigerant passes through fresh food evap coil? Won’t the refrigerant turn from liquid to gas in the first evap coil and therefore only deliver vapor refrigerant to the freezer evap coil? Generally, it goes evap coil – compressor – condenser in order to return the refrigerant to a liquid so that it can change back to vapor in the evap coil.
Only a portion of the refrigerant passing through the first coil turns to vapor. So a mix of liquid and vapor is then fed into the second evaporator, which turns into 100% vapor by the end of the coil. This way, you get cooling in both evaporator coils.
2. The last video states that the lines leaving the evaporator coils in a dual evap (with 3 way) merge together to form the suction line (3:50), which leads to the compressor. It later says when the fresh food compartment needs cooled, the compressor sucks refrigerant from the RC evap coil (5:39). Does it have the ability to suck refrigerant from only the RC coil, is that not what the video meant, or is that irrelevant?
The compressor sucks refrigerant from both evaporators, since the suction tubes merge before the compressor. However, if the 3-way vale (called the rotary valve in this video) is in a position such that one evaporator is closed, then no refrigerant will move through that coil.
4. I assume the reed valve is not fixable – requires new compressor?
Correct, that’s an internal component of the compressor, so the compressor must be replaced if the reed valve is damaged.
In the second video of 1.13 at 15:19, the evaporator fan is compared to the condenser fan. The evaporator fan is a BLDC fan with an inverter in the fan. I do not see where this fan has its own Line supply to convert into the 3 phase AC voltage that would power this BLDC. I believe I am confused
Little BLDC motors, like the ones used for evaporator fans, run on much lower voltage. This is why they usually take something like a 12 VDC power supply to their internal inverters. You just don’t need a lot of juice to run these guys. But they’re still doing the same thing inverters always do — making 3-phase power.
A compressor, on the other hands, needs a much higher voltage. Hence why compressor inverters take the full 120 VAC line supply.
I believe I understand that all motors must run on AC, and are named a DC motor if that is the power supply. The brushes commutate, etc. But for the compressor, why is it a BLDC motor if the AC input into the inverter is being used to power the compressor?
The inverter does output DC power, but this is then commutated by the switches into what is effectively AC power. Basically, the electronic switches in the inverter are doing the same thing the brushes do on a DC brushed motor. It’s simply being accomplished electronically rather than with physical brushes.
The reading mentioned internal thermal protectors (that require the compressor to be replaced), but the videos did not. Are they not prevalent in residential refrigerators?
Residential refrigerator compressors almost always have resettable thermal protectors. They are also usually external, especially on split-phase compressors. So the overload can be replaced separately from the compressor itself.
The reading mentioned internal thermal protectors (that require the compressor to be replaced), but the videos did not. Are they not prevalent in residential refrigerators?
PTC start devices are by far the most common start device for split-phase compressors.
I understand that I might test a compressor for continuity with ground. I understand that a compressor rotor will naturally develop leaks to ground, and that this is not an issue with the compressor (normal). If I measure and find continuity with ground, is there a way to know which it is? Or is is just one runs and one does not?
When paths to ground develop in a compressor, they are very high resistance paths. The continuity function on your meter would not pick them up. The path to ground would be something very high resistance, in the high k-ohms or mega ohms.
1. You said, “Or am I just assuming that based on appearance (rime ice buildup) that the defrost is not being initiated (if the peripheral components are proven good?” You’re on the money here. If defrost is being initiated properly outside of test mode and all of your peripheral components are good, then you should not have excessive frost buildup. In cases like this, putting the board into forced defrost is more of a confirming test than anything else.
2. If you jump L1 to DF, you’re just using a jumper wire to physically connect those two pins, bypassing the ADC. When the jumper connects those two pins, you’re simulating what the ADC does when it closes its internal switch and supplies voltage to the defrost circuit. So there’s nothing fancy going on here — you’re just manually bypassing the ADC.
3. If it’s the first trip, then you’re correct: the customer should leave the unit as-is, plugged in with the food in there and the doors closed. If necessary for disassembly, you’ll often pull the food out of the freezer yourself and put it wherever the customer wants it. One thing you could do is ask the customer to have a cooler on hand (if they have one) before you go out so that there’s someplace to put the food if you need to remove it.
4. Condensate drains can get clogged for a number of reasons. It’s a common side-effect of a defrost failure. Sometimes it’s just a fluke — like some kind of crud gets caught in the drain, and ice forms around it until the drain is completely plugged. Other times, there’s a design flaw in the drain, and there’s a replacement drain kit that needs to be installed (this was the case with an older Whirlpool refrigerator, not so common these days).
Either way, once you melt all the ice you can get with the steamer, that’s when you pour the salt water down the drain — if the drain hasn’t already been cleared. Often, the steamer is all you need to do the trick. You can tell that the drain has been successfully cleared when all of the water you’ve made by clearing it empties into the drain pan at the back of the refrigerator. As long as you’ve addressed any underlying issues that caused the drain to clog, you can reassure the customer that it won’t happen again.
And yes, the tubes referred to in the video are the evaporator coils.
You got it! Your reading of the schematic is absolutely spot-on.
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