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April 5, 2016 at 7:49 pm in reply to: APPLINCE MOTORS MODULE 8 VARIOUS FREQUENCY DRIVE SYSTEMS #9889
Remember what PWM stands for: Pulse Width Modulated. The signal sent to the inverter board is a series of DC square wave pulses. During a pulse, the board is sending out 5 VDC, and between pulses, the board is sending out 0 VDC. If you measure this signal with your meter, it will take the average of these two voltages, meaning that you will read 2-3 VDC.
The voltage at the switch’s contacts actually has no impact whatsoever on whether or not that switch will actuate. The switch is opened and closed by the timer motor, not the current flowing through it. There could be 0 volts present at either of the switch’s contacts, but if we’re at the point in the cycle where the timer is supposed to close that switch, it will still close the switch–assuming the timer is functioning properly.
The test you proposed doesn’t actually tell you whether or not the drain pump is getting neutral during normal operation. The pump only gets neutral through 11-14 on the float switch in a situation where there has been a flood or a leak. Testing from A1 to A12 with a loading meter is the most surefire test to do, and also the easiest, since you can access both of those points right at the timer.
The test that Scott did around 1:48 did not actually confirm whether or not L2 was present, nor was that its purpose. The purpose of that test was only to tell if that timer switch was closing properly or not.
Measuring 0 volts across that switch only tells you that it is closing. You get the same result if you measure across a closed switch with both L1 and L2 present, as was not the case here, OR if you measure across a closed switch with only one line present, as was the case here, since, as you said, L2 could not reach that point in the circuit due to the open thermal fuse.
When a component in a circuit drops voltage, that means that energy is being lost in the circuit. However, we know from the first law of thermodynamics that energy cannot be created or destroyed, only transformed from one form to another.
This means that whenever a component drops voltage, it must be transferring that energy to somewhere outside of the circuit. In other words, it’s doing work. More often than not, this work manifests as heat energy.
Heating elements, for example, are essentially just large resistors that are specifically designed to give off heat, and they do this by dropping voltage whenever power is supplied.
This is also why loose connections can get hot and cause damage. A loose connection between wires creates a sort of unintentional resistor in the circuit, which drops voltage and therefore produces heat.
As for your question about Vcc, I believe that was covered in Module 3, Unit 4.
Sorry for the delay in responding. Let me try to answer your questions.
If there’s a fan in the FF compartment, then you’re most likely dealing with a dual evaporator unit. There are cases when a fan will be present in the FF compartment in a single evaporator unit simply to help with air distribution, but this is pretty rare. The best way to find out what kind of fan is present on any particular unit is by looking at the tech sheet or parts diagram.
As for inaudible evaporator fans and compressors, that’s sometimes the case. Variable speed compressors, for example, can run very quietly. The best way to check out if they’re functioning is by accessing the control board, identifying your test points on the schematic, and testing for voltage drop across the load, or testing for current in the case of a variable speed compressor, since there is an inverter board involved.
You’re on the right track! In a 240 VAC circuit, L1 is acting as the return path for L2, and vice versa. And since this is AC we’re talking about, the polarity is constantly reversing. So in one moment, L1 would be positive and L2 would be negative, and then the next moment L1 would be negative and L2 would be positive. A neutral is not actually even needed in a 240V circuit, only in a 120V circuit.
The answer to this question gets a little bit into what you might call the “art” of appliance repair. Some brands tend to have flakier thermistors than others (Samsung, for example) and you only get a feel for that by working the trade and getting a feel for the little nuances. For someone starting out, it’s usually better to be safe than sorry and test a thermistor at a couple different temperature points to make sure that it’s good.
The yellow wire runs from the water level switch to pin 16 on the timer. Any point along that yellow wire is indeed electrically equivalent to pin 16, if that is what you’re asking.
Yes, if a load is getting the voltage it should get and has a path to neutral, and the load still is not running, then the load is bad.
Conversely, if a control is not providing a valid power supply when it should be, then you can deduce that it is bad.
And nice to meet you too, Sal. 🙂
Yes, AC and DC circuits each have separate grounds. Remember that voltage is never absolute–it is always relative to another point. In order for the measurement to be meaningful, you have to measure with respect to the correct reference. DC voltage must be measured with respect to DC ground, and AC voltage must be measured with respect to neutral.
Another important thing to remember is that neutral and AC ground, while they should (if everything is wired properly) have the same voltage potential, serve completely different purposes. Neutral is the return path for AC current flow, whereas AC ground is there as a safety precaution, to ensure that current leaking to the chassis is discharged without harming anyone making contact with the appliance.
As a rule, you shouldn’t make AC voltage measurements with respect to AC ground, because this is assuming that, among a few other things, the appliance is properly grounded. And unless you have proven that, you cannot make that assumption. Instead, always make AC voltage measurements with respect to neutral.
A wax motor consists of a PTC thermistor which, when power is applied to it, heats up, in turn heating up a specially engineered wax within the motor. As this wax heats up, it expands, and this expansion pushes out the plunger of the motor. This is how wax motors used as door locks hold the door closed–for as long as that wax is heated, the plunger will remain extended, preventing the door from opening.
This is also why it can take a few minutes for the lock to release after the appliance has finished operating. The wax has to cool down enough for that plunger to retract.
Wax motors–among many other important topics–were covered in a webinar from a couple weeks back. Click here to go to the recording.
It’s at Appliantology.org, so make sure that you’re signed into your Professional Appliantologist account over on that site, otherwise you won’t be able to view it.
There are two different diagrams present on this tech sheet: the wiring diagram, and the schematic diagram. Remember that a wiring diagram is a representation of the circuitry as it is physically, and the schematic is a representation of the circuitry as it is electrically. As a technician, your go-to diagram should almost always be the schematic, since it shows much more simply than the wiring diagram how electricity moves through the appliance.
When you look at P25-2 and P30-1 on the schematic, I think you should see that it’s very apparent why they are electrically equivalent, as well as whether the relay board switches the path to line or neutral.
Diagnostic modes work differently for different models and appliances. Some display the error codes at the end of a test cycle, some at the beginning, some interrupt the test cycle when they sense an error, and some require you to go through a different procedure entirely to access the error codes. Whatever the case is for a particular model, its tech sheet should tell you what you need to know about how to access the diagnostic mode, run a test cycle test cycle, get error codes, etc.
As for testing components, the whole purpose of running a test cycle is to take measurements of components while they are running. For example, if you wanted to take a measurement of the drain motor on your dishwasher, you would enter diagnostic mode, advance the test cycle to the point where the control board is supposed to run the drain motor, and then measure the voltage going to the drain motor from the control board–using your loading meter, of course.
No, we don’t go very deeply into dishwashers specifically, because our goal is not to provide product training–our goal is to give you all of the tools you need to effectively troubleshoot any appliance through deductive reasoning and a solid understanding of basic electricity.
So you don’t need to be intimidated by dishwashers. The fact that they’re hardwired into the house doesn’t make them any different electrically from other appliances, and it doesn’t stop you from shutting off power when needed. You simply need to locate the circuit breaker for the dishwasher and switch it off.
And yes, just as with any other computer-controlled appliance, you can test dishwasher components from the control board using EEPs. In fact, here’s a video of us doing just that on a service call, for your viewing pleasure.
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