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Hi Dennis,
The amp measuring function on your multimeter measures DC amps (current) not AC amps. You need a clampon amp meter to measure AC current.
In appliance repair, you will never need to measure DC amps so the amp measuring function on your multimeter will never be used.
Let me know if that doesn’t answer your question.
Hi Walter,
It’s like testing a single wire with 120v voltage present. There is no potential from any part of the wire to any other part of the same wire. But if there’s a load that voltage becomes measurable at the load? So hypothetically on a ungrounded or open neutral scenario on a 120v heating element, measuring both sides will give you 0 but either side to ground or neutral will give you 115-120 and that is true voltage because the potential is there. But when the neutral is connected and the element/anything is pulling any amperage you can measure 120 at the element/anything terminal to terminal and that’s called a voltage drop.
This is all correct. voltage causes current to flow and is the prime mover of electrons.
But when that current flows through a load, it produces a voltage drop across that load. If it is a simple series circuit with a single load, and then the voltage drop across that load will be exactly equal to source voltage, no more no less.
Now suppose there are two or more loads in series with each other? What will the voltage drops be across each load? This is what Ohm’s law tells us: E = I * R.
So is it not really true voltage if it’s under load, path of least resistance coming into play here?
Not sure what you’re getting at here with your reference to “path of least resistance.” BTW, that “Path of least resistance” thinking will get you trouble! I hear techs using this statement all the time and it is very misleading.
For example, if current always follows the path of least resistance, then why do parallel circuits work at all? For example, suppose I have a parallel circuit consisting of a 10 ohm resistor and a 50 ohm resistor. Well, if current always follows the path of least resistance, then why doesn’t all the current only flow through the 10 ohm resister? Why does current still flow through the 50 ohm resistor in parallel with that 10 ohm resistor?
The answer is because current will follow all valid paths regardless of resistance.
Your questions have made me think that this would be a good topic for a blog post, maybe even a pop quiz at my Facebook page. Stay tuned!
Good question, Walter. Understanding the difference between voltage and voltage drop is a key electrical concept to understand.
Voltage is simply the difference in electrical potential between two points. An example is measuring the voltage at an outlet or to the terminal block on an appliance.
Now, keep in mind the concept that voltage can cause current to flow. This is why voltage is also called “potential” because we say that voltage has the potential to cause current to flow. If that voltage is connected to a valid circuit (conductors, loads, no opens) then current will flow because of that voltage.
Now when that current flows through a load, it will produce a voltage drop (or deposit) across that load in accordance with E = I*R. In other words, the voltage drop across the load will be directly proportional to the current flow through that load and to the resistance of that load.
If you measure voltage across a load that has current flowing through it, you are measuring a voltage drop, not voltage.
The difference is whether or not current is actually flowing through a load or not.
Does this help clear it up?
Hi Igor,
The refrigeration cycle in commercial refrigeration equipment works exactly the same as residential refrigerators. The big differences will be the size of the compressors (much bigger), the use of thermal expansion valves (TXVs) vs. capillary tubes to supply high pressure refrigerant liquid to the evaporator and sometimes additional components like accumulators used to “pump down” the system for service.
The trade group, Refrigeration Service Engineers Society, offers training courses and reference manuals. If you’re really going to get into commercial refrigeration, it’s a good group to join. You probably won’t need their training because you already know the basics but they offer some good reference manuals for sale that would be helpful for servicing commercial refrigeration equipment.
We don’t have any plans on offering training courses in commercial refrigeration. The Academy will stay focussed on residential appliances and we’ll be rolling out courses on other equipment such as front load washers and cooking equipment in the near future.
Scott
Hi Dennis,
EEPs are points that look exactly the same to electrons. The two characteristics of EEPs are:
1) They have electrical continuity. In other words, if you measure the resistance between two points that are electrically equivalent, you will measure zero. It would be like measuring the resistance in a section of wire.
2) There is zero voltage difference between points that are electrically equivalent. If you were to measure voltage across two EEPs, you would read zero, even if both points were at 120vac.
Does that help clear it up?
The wording is confusing and is one of the things to look out for with both the Samsung and LG documentation: Korenglish. Maybe in the input test description they weren’t distinguishing between the main and sub PCBs. But the schematic tells the real story and that’s the main point with this question. Good job for sticking with it!
No worries about thinking there was a error in the quiz! Let me see if I can help you figure out the correct answer without just telling it to you…
Looking at the list of items displayed on the display board during self test isn’t a specific indication of which board is getting that particular input. There are several boards in this washer. To know which board is getting which input, you need to look at the schematic and board pinout diagrams.
I hope one of the things any ASAT student gets out of the course is a basic reflex to get eyeballs on the schematic for any appliance problem they’re working on!
Let me know if you need another hint. 🙂
One of them is a correct answer. If you have specific questions about why you think a particular answer should be the correct one, I’d be glad to discuss that with you.
Hi Tyler,
It’s a parallel circuit problem, just like you studied in the Basic Electricity module in Fundamentals. The condenser fan motor and compressor are wired in parallel and you’re asked to find the equivalent parallel resistance.
Review the Series-Parallel screencast in Fundamentals and see if makes sense then. If you’re still unsure, let me know which part of the question is confusing.
Hi Patricio,
You don’t need to answer the later-added quiz questions in order to see the new content. But you do need to complete the module exams if you’d like to see the new material. That’s not our call– it’s just one of the limitations of the learning management software we’re using to run the courses.
If you’d like to re-do all the quizzes, we can reset you to the beginning of whichever module you like. We’ve had many students and alumni opt to do this is a more thorough way of reviewing the material and taking in the new stuff. Let me know if you would like this– it’s no trouble at all to set this up for you.
Scott
Hi John,
The correct answer is given but you need to convert the units. The conversion from psi to inches wc was given in the previous lesson: 1 psi = 27.7 “wc. So 60 psi = 1660 inches wc which is the answer given. Ya gotta watch them units! 🙂
Hi Tyler,
I think you got the idea. I’ve unblocked you so you can move on to the next lesson. Let me know if you have any questions.
Hi Todd,
When I wrote that question, I had in mind the exact situation discussed in the screencast where the timer wasn’t advancing in autodry when the dryer thermostat was open– because L1 was applied to both sides of the timer. Because of that, the question was imprecisely worded. I have since edited the question to clarify this.
@Tyler: I’ll reset your quiz but before you take it, you may want to review a new screencast I added to M3, U6 of the Fundamentals course on Household 120/240 VAC Single-Split Phase Electrical Power Supply Systems. L1 and L2 are 180 degrees out of phase with each other and so do create a voltage potential difference when applied across a load.
Hi Josh,
It’s more like your second statement, the voltage is “dumping” onto the load. The main thing to keep in mind with voltage drop is, as stated in Unit 8:
A voltage drop across a load is produced when current flows through that load.
The source voltage stays the same (or at least we assume that it does). Voltage drop only refers to the voltage across the load, not the source.
The amount of voltage dropped across that load is determined by Ohm’s Law: E=I*R
With electricity, you have to keep a few simple equations in mind to keep your thinking straight, there’s just no getting around it. Trust the equations, they work! But they also show you the relationships between voltage, current, and resistance.
If a customer smells gas isn’t it a good idea to call the gas company to investigate?
Why not call you? Most gas companies don’t work on appliances. Some do; but most don’t. And if you have the skills to actually go inside the appliance and locate a leak (honestly, what kind of skill are we talking about: squirting bubbler solution on gas supply tubing joints and connections) then why shouldn’t you be the go-to guy?
OTOH, if you don’t have the skills to squirt a bubbler solution to gas tubing joints, then you should absolutely advise them to call the gas company.
I get it that LP gas is lighter than air and will accumulate at floor level.
LP gas is HEAVIER than air– that’s why it will accumulate at floor level.
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