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If by positive and negative you mean DC voltage and DC ground, then yes, that would be correct for the four wire configuration you described.
I’ve never encountered a damper motor that was not a stepper, and this is because dampers are an application that stepper motors are uniquely suited for. Stepper motors move in set intervals, and they’re designed to only move so far in one direction or the other. This way, a control board can just tell a stepper motor to open or close the damper and not have to worry about sensing its movement or telling it to stop at a certain point.
Stepper motors have two separate windings, one for rotation in one direction, and one for rotation in the other. This would explain your four wire configuration–the board activates one winding when it wants the damper to open, and the other when it wants it to close.
As for their power supply, all stepper motors run off DC power. If it looks like a stepper motor has an AC power supply, that just means that there is a rectifier built onto the motor, which turns that AC power into DC power for the motor to use.
November 4, 2016 at 12:43 pm in reply to: Question about schematic used in quiz question 4 and 5, unit 5 part 2 #11319Since you asked, I can explain a little about how noise filters work. That’s not a transformer in there. That resistor and those capacitors and coils that you see all serve to filter out high frequencies generated by the appliance (“noise”) and prevent it from leaking back into the main power supply. There’s no stepping up or down of the power.
However, how the noise filter works is actually not important to answer that question. In fact, that question was created specifically to see if you can apply basic troubleshooting strategy to something that looks very complicated. All that you need to do is identify where your inputs and outputs are and how you would test for them. In fact, even though this diagram shows all the individual components of a noise filter, in reality, noise filters nowadays are just self-contained little chips. If your tests were to show that the noise filter is bad, you would just change it like any other part.
You answered your own question! Yes, that yellow wire carries the PWM signal from the board, and by hot-wiring that to the positive terminal of the battery, it’s simulating the board telling the fan motor to run as fast as it can.
We pulled the unit out because we needed to access the components in the heater circuit. There’s no way to test the voltage across each component individually without physically getting access to them.
To answer your first question, yes, we had the unit in diagnostic mode to test the voltage supply to the heater. That way we could reliably know that the board was in a state where it was supposed to be supplying voltage, and we could test whether it was doing its job.
As for your second question, I recommend you re-watch the video, because the Samurai spent the whole first half of it showing how he proved that the board was providing a good voltage supply. Once he had done that, he moved onto testing the voltage across each load in the heating circuit to see which component was open.
Remember that when you do a voltage test, you’re measuring the voltage difference between your two probes. Measuring 0V across the heater proves that it’s good because it shows that it is closed. In fact, there was actually 120V on either side of that heater, since no current was flowing through the circuit and thus no voltage was being dropped across the heater. The difference between 120 and 120 is 0, so that’s what the meter showed.
Towards the end of the video, he shows that he’s measuring 120V across the float switch, indicating that it is open (when it should be closed) and implicating it as the bad component in the heating circuit.
Technically, yes, the compressor and condenser fan are dropping some voltage. But to tell exactly how much voltage, you have to calculate the equivalent resistance of those parallel circuits. Scott goes through this in that unit’s video. I recommend that you review it from the 9 minute mark to the 12 minute mark.
As shown there, the resistance of those parallel circuits is so low in comparison to the resistance of the evaporator fan that they would be dropping a minute amount of voltage, so little that the compressor and condenser fan would not actually do any work.
October 17, 2016 at 10:56 am in reply to: What characteristic of a heating element does NOT make it an electrical load? #11009The wording of this question is a little tricky. As you know, when a heating element is in a circuit, it is a load. So clearly the question isn’t saying that a heating element isn’t a load.
A heating element has various characteristics, not all of which are necessary characteristics of a load. What it’s asking is this: which quality does a heating element have that is not an essential quality of a load?
What Scott said about looking up the technical literature is key. I found what I’m pretty sure is the correct model number for your machine, and a quick look through the documentation answers your question.
In the parts diagram, you can see exactly why you can’t put this model into any kind of diagnostic mode: it has no interface for doing so! The only controls that this model has are some mechanical knobs for controlling the temperature. While that ADC board may technically be a “control board”, it is not a microprocessor board, so there is no way to communicate with it.
This highlights exactly why you need to find whatever technical documentation you can for the appliance you’re working on and look through all of it carefully. Most of the time the answer to your questions is right there waiting for you.
As a general rule, you should always use a loading meter first thing when you’re making measurements (unless you’re measuring control voltages). If you get a good reading on your loading meter, that confirms that you have both a good voltage supply and a good neutral. If you get a bad reading on your loading meter, then you know that you have a problem with your power supply, and you can investigate further from there.
Yes, that’s correct. Before concluding that the board is bad, you need to check that all of its inputs are good, and that means testing the thermistors and comparing their resistances/voltage drops to a temperature chart.
By “between”, we just mean that the winding is connecting those two terminals. So yes, as you said, physically between.
However, you haven’t correctly identified the terminals that the start winding is between. Look at the question again, and remember: the start winding has higher resistance than the run winding.
In order to run the motor, an inverter board needs two inputs:
- 120 VAC
- A good PWM signal from the main control board
If the inverter is receiving both of these things and still not running the motor, then that implicates the inverter.
You’re correct that when you measure a PWM signal, your multimeter will read an average of that signal, since it’s an oscillating square wave. If you test for that PWM signal coming into the inverter board and do not detect it, that does not implicate the inverter board, but rather the main control board, since that’s what is supposed to generate the PWM signal.
When you say that you tested the thermistors, do you mean that you just ran the board’s built-in thermistor test, or did you measure the resistance/voltage drop accross each thermistor and check it against a temperature chart to make sure it’s in spec?
If you only ran the board’s test, that’s not conclusive. The board can only check if a thermistor is completely open or completely closed. However, this is rarely how thermistors fail. Usually, a failed thermistor’s resistance goes out of specifications, but without opening or shorting, and you can only test this by doing it yourself with your meter.
But, if you did test the thermistors in the correct way, and they are indeed still good, then we’re left with a situation in which the evaporator fan is good, the thermistors are good, and yet the board is not running the fan. In this case, the board’s logic is for some reason saying that it should not run the fan.
To figure out why this is the case, you have to find the service manual for the specific unit you’re working on and look up how this board’s algorithm functions. Without knowing those details, your diagnosis can’t get any more specific.
Nice find! Hope it works out well for you.
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