Troubleshooting is the higher mental function that separates the real technicians from the parts changing monkeys. A technician who knows how to use that gray stuff betwixt his ears to ask himself the right questions can fix any appliance, whether he's been "trained" on it or not.
Troubleshooting is not just replacing a part that's bad-- that's called parts changing. Troubleshooting is the systematic, logical progression of tracking down the cause of a problem. In accordance with the 6th Law of the Prophecy, the troubleshooting process begins right at the problem-- in other words, at the thing that ain't doing its thang. You then work backwards, checking inputs and outputs for each component in the work flow, whether electrical or mechanical.
This is the big secret to successful troubleshooting: checking inputs and outputs. If you just keep this in the front of your mind while you're trying to figure out what's wrong, it will lead you to the problem or bad part. And it doesn't matter if you've not been trained on the particular appliance because, in the course of checking inputs and outputs, you will naturally ask yourself exactly the right questions you need to answer in order to solve the problem.
For example, a refrigerator is warm in both compartments. You find the compressor is running but the condenser fan is not running. So you start troubleshooting right at the condenser fan motor. You ask yourself, "What are my inputs and outputs?" Say it aloud. Don't worry if the customer hears you talking to yourself-- at this moment, they don't matter; it's just you and the puzzle before you.
The output part is easy: fan blade movement: there isn't any. But what about the inputs? A fan needs voltage to operate. Okay, fine, but what kind of voltage? DC? AC? Pulse-width modulated? Don't know? That's okay! Now at least you have asked the right question and you now know what information you need in order to continue solving the problem.
At this point, you might look for clues on the fan motor label or on the tech sheet behind the toe grill in front. This is where training on the specific appliance can help you because it can give you the specs for many of these components. But you could be trained up the wazoo and still not approach this problem like a real technician who knows how to troubleshoot.
Let's look at a real-life case study:
I recently batted cleanup behind a local parts changing monkey (PCM) in my service area who advertises "30-years experience, factory trained." He was working on a GE front loading washing machine that overfilled. He tried to fix the problem by blindly replacing parts, hoping to get lucky. Of course, he failed miserably but that didn't stop him from charging the customer anyway. The customer called me out of frustration and desperation and it turned out to be a very simple problem that the PCM would have found if he had just done some troubleshooting like a real technician.
The other thing this video illustrates is the importance of understanding how the components inside an appliance are supposed to work together. How else can you troubleshoot? In this case, with the washer overfilling, starting troubleshooting at the water inlet valve is not a bad idea BUT what are you looking for? The PCM simply guessed and hoped to get lucky. But there's no need to guess if you understand how the valve is supposed to work and can make a simple voltage measurement.
In this case, you would use your meter to see if the valve is still getting voltage when the drum was overfilling. If so, then the problem is NOT the valve, but in the component that controls the valve. Here, the pressure switch controls the valve and this is the next thing the PCM replaced. But, again, there's no need to guess because the switching function of the pressure switch can be tested using your ohm meter and gently blowing into the pressure tube to see if the pressure switch contacts change.
Actually, in the process of gaining access to the pressure tube to test the pressure switch, he would have discovered the chaffed pressure tube in the course of doing simple troubleshooting like a real technician and not just blindly thrashing about, throwing parts at the machine and ripping people off.
So, putting this all together, here's a simple operational description of how these parts work together inside the washer:
As the water level in the drum rises, the pressure inside the pressure tube increases. This increased pressure is felt by the pressure switch which is calibrated to switch contacts at a specified pressure corresponding to a design fill level. The pressure switch, which was sending voltage to the water inlet valves during fill, then cuts voltage to the water inlet valves and the wash cycle begins.
It is apparent that if the pressure tube is leaking, the pressure switch will not get the proper input (change in air pressure) and so will not produce the proper output (cutting voltage to the water inlet valve).
How is it that someone who repairs appliances for a living does not understand this?
Troubleshooting is not mysticism; it is reason and logic. It begins with asking yourself the right questions, "What are my inputs and outputs?" Getting the answers to these questions will naturally lead you to the solution to the problem and a successful appliance repair.