Forum Replies Created
-
AuthorPosts
-
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.
No calculations needed! You just need to look at the temperature chart in the tech sheet and see if it shows values for resistance or voltage.
If it shows voltages, then all you have to do is measure the voltage drop across the thermistor (while the fridge has power and both thermistor leads are still connected, of course) and then compare that to the chart.
If the chart only shows resistances, then, like you said, you’ll need to disconnect one of the leads to measure the resistance of the thermistor, then compare your resistance reading to the chart.
And of course, you also have to know what the current actual temperature in the compartment is, so that you can tell if the thermistor is within specifications or not. You’ll want to use your IR temperature gun for that.
Hi Gene, I’m Sam, the guy who accompanies the Samurai on all his quests for appliantological resuscitation–otherwise known as service calls. That means that I end up carrying the tool backpack in and out of every home.
I can tell you that the pack weighs about 32 pounds. That may sound like a lot, but it’s actually not bad at all when it’s on your back, especially considering all of the useful stuff we have stowed in there.
Hey Dennis! Not the Samurai, but I’ll try to help clear things up for you. It sounds like you have a decent grasp of this, except for a few points that I can address.
First, remember that, at least in North America, the standard voltage at outlets for appliances like electric dryers is 240 volts, not 220. And, if you are working with a 220 volt outlet, you would measure 110 volts from L1 or L2 to neutral, not 120.
Second, the last question in your post seemed to indicate that you’re still a little fuzzy on the relationship between voltage and current. Don’t sweat it. These things can be a little counterintuitive.
As you correctly said, voltage is the potential for current to flow. Or, how I like to think about it, it’s a measure of how much the electricity wants to flow. Current, on the other hand, is the actual flow of the electricity.
Something that’s very important to understand is that in order for current to flow, there must be voltage present. Voltage does not “become” current. It exists at the same time as current, and, again, must be present in order for there to be any current flow.
So in your example, when you plug in the dryer and turn it on (thereby closing the circuit), you would measure 120 volts from L1 or L2 to neutral, and 240 volts from L1 to L2, assuming you’re measuring at points that have uninterrupted connections to their sources at the outlet. You would also be able to measure current, because the two requirements for current flow have been met: voltage being present, and a closed circuit.
I hope that helps you out!
Hi John,
Here’s a download link for a pdf version of the textbook, laid out exactly like the print version, page numbers and all. This should make it a lot easier for you to look up references from the course.
Click here to download the pdf document.
Enjoy the rest of the course!
-
AuthorPosts
