Susan Brown

[Susan Brown]

Our answer is basically describing the logical flow of thought – we don’t mean for it to imply that you shouldn’t look at the schematic and determine where/how you’re going to do your measurements.

[Susan Brown]

Hi John,

The answer we’re looking for is, “Follow the line cord inside the machine, measuring voltage as you go, to find where you’re losing the voltage”

Because when there is absolutely nothing going on – no lights or responses to key presses – then you are losing voltage somewhere between the outlet and the controls (the board, assuming it has one).

[Susan Brown]

We don’t give the answer in a neat and tidy way – what we want is for you to apply what we teach about inputs and outputs to this question.

Inputs to a control board would be information that the board can then make “decisions” about. So, sensor data or a feedback signal, for example.

Outputs from a control board are generally things that will be used by the loads or a sub-board, like power supplies.

If you have trouble identifying which of our answer choices fall into which category, send me and email and we can go over that privately (so we don’t give the answers away here).

[Susan Brown]

Thanks, you too!

[Susan Brown]

You can continue on, since we grade those pretty quickly (same day, usually) and you can then use your second attempt. It’s just best not to go *too* far until you’ve passed it, just in case.

[Susan Brown]

You’ll see at least one like that in Module 4 (unit 2).

[Susan Brown]

No problem! You’ll see it mentioned again in the Troubleshooting module.

[Susan Brown]

Hi John,

The question is, ” What would happen to the evaporator coil if the defrost heater failed open?” There is no “to” before “open”. An important difference!

For a heater to “fail open” means that it is electrically open somehow, and electrons are not able to move through it. Often the heater material has a break in it.

Make more sense now?

[Susan Brown]

If the entire appliance is unresponsive (no lights or anything), the very first thing you check is to see if 120v is present at the wall outlet.

[Susan Brown]

Good! Glad to help.

[Susan Brown]

Because L1 and L2 are 180 degrees out of phase with each other. When one is +120v, the other is -120v. We first describe this in Mod 4, unit 6, then I talk about it some more in that video in Mod 4 unit 9.

[Susan Brown]

In a *functioning* 120v circuit, with one load, you will have line (hot) on one side of the load, and neutral (ground potential) on the other. So when you are measuring for voltage drop, you will put your probes on either side of the load (or EEPs corresponding to either side of the load) and see if you get voltage. If current is flowing through that load, you will measure a voltage drop, which should equal the source voltage (because we’re talking about a circuit with one load).

If current is not flowing through the circuit, because it is open somewhere, then you will either not have line or neutral present at the load. In either event, you would measure 0v across the load because you would be actually measuring line wrt line, or neutral wrt neutral, depending on which side of the circuit is open. In this case, you could then do a measurement of voltage with one probe at one side of the load, and one probe on a known-good neutral. If you get line voltage here, then you know the open has to be on the neutral side of the circuit, because we only get voltage from the line, or hot, side of the circuit.

If you have a 240v circuit, these things are a little different. Do you remember Question 9 on the Midterm exam where we had to disconnect one side of the circuit so we could figure out which side was open?

Does this help?

[Susan Brown]

Hi Jon,

It’s good to be thinking through these things!

In the first instance, with the light off, you were measuring the voltage potential at the outlet.

In the second, with the light on, you were measuring the voltage drop across the load (the light).

You are correct that if you measure across a closed switch you would expect to measure 0v, but you didn’t have your probes just on either side of the switch – you had them on either side of the working part of the circuit – the light bulb.

Does that make sense?

[Susan Brown]

Thanks! I just added an exception to that “Pro-tip” (if the valve has a removable plastic filter, you can clean or replace that)

[Susan Brown]

They do, but one half of it can trip without tripping the other side. We aren’t saying it happens a lot, but it is common enough that you always want a customer to check it if they report certain things.

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