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How could a condenser fan cause partially frosted coil?
Scott actually spends about a minute in the Module 2 unit 2 video explaining how a bad condenser fan can cause a partially frosted evaporator. Give it another watch, and if the explanation still doesn’t make sense, let me know what about it is giving you trouble.
This is the kind of thing that the Appliantology forums are great for! At Appliantology, you can easily attach images to posts, and you can get input from other technicians as well as us. Plus, you get to flex your shiny new MST Student membership.
One of the forums at Appliantology is called The Dojo — you can find it by reading through the forum listing on the homepage. Post your schematic question there as a new topic, and we’ll help you out with it.
I see you edited your reply. Rewatch the video, and reread the text description before it in the unit. Was the problem that the board wasn’t supplying power to the damper?
Right again!
Now let’s turn this back to the damper motor. That motor is just a normal load — nothing special about it. When you read across it with your meter, just like the Samurai did in the video, what would you expect to read?
Correct!
Now what if you have that same circuit, but it only has one load in it? What voltage drop will you read across that single load?
Sure, let’s try an example to make sure you have a clear idea of voltage drop. Note that this isn’t the same circuit as the damper’s, but it doesn’t need to be. Once you get this concept, you’ll see what’s going on with that measurement across the damper motor.
B1 has equal resistance to B2. If you use a voltmeter and measure with one probe on either side of the load marked B1, what will your meter read?
Clearly the damper was bad, but why was the control board also bad? It said 120v so the circuit was open but why did you say it was supposed to switch?
The meter was reading the voltage drop across the damper motor. You can see that the probes are placed directly in the harness for the damper. That 120 volt reading does not mean that the circuit was open — it means that the switch on the board was closed and supplying voltage. If the circuit had been open, he would have read 0 volts because there would have been no power supply.
As for why it’s supposed to switch, you can use common sense for that. Should the motor be energized at all times? Its job is simply to open or close the damper, so it should only be energized when it’s supposed to be doing that.
Note the * character in the model number provided by the manual. That’s an asterisk, and it serves as a wildcard character. That means that, no matter what character occupies the same spot as the asterisk, this manual applies to that model.
Correct, circuit diagram is yet another term you’ll see thrown around. The important thing to learn is how to identify what a schematic looks like — that lets you tell that it’s a schematic regardless of what label it has.
Service manuals don’t always use the most precise terms. What they’re calling a wiring diagram is actually a schematic—you can tell because it’s readable, not a tangled mess of lines.
I keep hearing the term inverter and inverter board. Are they the same thing or different? I remember in the previous lessons Inverter Board is another name for VFD?
No, there is no difference between an inverter and an inverter board — those terms refer to the same component. And an inverter is a component of a Variable Frequency Drive, not a name for the VFD itself.
If BLDC and brushed motor both have commutator, what is the need for the inverter to convert DC into AC for motor to use? THanks
A BLDC motor does not have a commutator. Remember, in a brushed motor, the brush is the commutator. But a Brushless DC Motor doesn’t have a brush, and therefore has no built-in commutator. That’s where the inverter comes in.
A Variable Frequency Drive (VFD) is a system not a type of motor. A VFD consists of a computer board, which sends pulse width modulated signals to an inverter board, which in turn interprets those signals and sends power to a BLDC motor.
I recommend you rewatch the videos if this still isn’t clear. After doing that, let me know if you have any more questions.
Thanks for the answer. I still don’t understand exactly why he wanted to see the exact resistance on those 2 loads? Wouldn’t doing the continuity test sufficient enough?
Normally, yes, a continuity test would be sufficient. Scott wanted to take a resistance measurement for pedagogical purposes — he wanted to show the resistor and the heater’s resistances adding up.
Can you use resistance check to test for continuity OR to test if loads in a circuit are working?
Yes, you can use a resistance measurement to check for continuity — a continuity measurement is just a dumbed-down resistance measurement. You cannot, however, test if a load is working with a resistance measurement. You can see if it is electrically within specifications, but there could be other things wrong with it.
When do i have to use resistance test?
When you’re checking a component’s resistance against specifications. If a particular heater is supposed to have a resistance of 10 ohms, you can do a resistance measurement to confirm that.
Is continuity test only used to find breakage within circuit lines?
Good question! Yes, that is essentially all you would use a continuity test for.
All of these questions get talked about in detail in the last video of Module 5, unit 4. If you haven’t watched it already, go ahead and do so! It will help clear things up a lot.
Why wound’t he use use Continuity testing for this case instead of resistance testing?
Because he was interested in seeing the exact resistance of those two loads — continuity would only tell if the circuit was open or closed.
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