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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.
It will not! That is in fact one of the huge reasons why you should only ever use a steamer and never a heat gun. Heat guns can wreak all kinds of havoc in a refrigerator, not just to the plastic lining, but also to the evaporator coils themselves. On the other hand, you could hold the nozzle of a steamer right up against a piece of plastic, and it wouldn’t harm it in any way.
All correct, except for one thing. You could check the continuity of the switch, but that should not be your confirming test. An Ohms measurement should only ever be a preliminary test. If a component fails an Ohms test, then it’s bad. But if it passes, it could still be bad, and you need to follow up with a voltage measurement to be certain. Switches, especially timer contacts, can fail when power is applied, so the only way to check for that reliably is with a voltage test.
No, you cannot assume that the valve is bad–you can definitively conclude that it is bad, and that’s a very important distinction. There is no ambiguity here. If you measure 120 volts in the valve’s circuit with your loading meter, and the valve is still not functioning properly, then the only conclusion you can draw is that the valve is bad. Which is a good thing, because it means you can be absolutely certain that your diagnosis is correct.
You assume correctly! From there, you can make the very simple deduction, with no ambiguity, that your problem lies somewhere besides the valve itself, and you would proceed by troubleshooting anything that could interrupt line or neutral to the valve.
This is why a loading meter is such a powerful tool–in one simple test, it gives you enough information to make a definitive deduction, without having to worry about being tricked by open neutrals or ghost voltage or any fake-outs like that. It’s just up to you as the technician to have enough confidence in your reasoning to make the next step in your troubleshooting.
In order for any load to operate, it needs to have a valid power supply. That doesn’t just mean 120 volts at the load. Remember P = I x E? Power is both voltage and current. You need both in order for a load to do work. The simple, elegant way to test for a valid power supply is by using a loading meter.
For your inlet valve, you would simply set up the leads of your loading meter in parallel with the valve in order to check if it has a valid power supply. In one test, this will tell you whether or not that load’s circuit is getting 120 volts and has a valid path for current flow.
Now, if you use a loading meter to test that inlet valve, and you measure 0 volts, what conclusion should you draw from that?
A clamp-on ammeter measures current by sensing the magnetic field given off by the wire enclosed in the clamp. So theoretically, another hot wire that’s close to the clamp could produce some interference, but this rarely happens.
If you’re concerned about it compromising your measurement, you can just hold the wire out of the way a bit with one hand–it doesn’t take too much distance to eliminate any danger of interference.
As with any troubleshooting scenario, what you want to start with is a load analysis. The load of interest here is, of course, the heater, since we want to know whether it’s getting line or neutral from the Heater PCB.
The first step in this particular case is to decide which schematic to use, since there are two provided in the tech sheet. One is labelled as having the heater, and one without. I think we both know which one we want to use here. 🙂
Next, we find the heater on the schematic, and we look at what it’s connected to on either side. The side that’s connected to the Heater PCB is, of course, going to be connected to it through the Heater Relay, even if it’s not explicitly marked as such.
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