Scott Brown

[Scott Brown]

I opened the panel of the unit but could not find the diagram.

Gotcha covered: Frigidaire FFLE1011MW2 Stacked Laundry Center Tech Sheet 137539400

Take a look through the tech sheet. The first part is the dryer. The schematic is at the end (after you scroll through all the other languages).

– What do you notice right off the bat about the dryer “timer”?
– How does this inform your troubleshooting strategy? (hint: remember from the TST special notes about loads with algorithmically-controlled power supplies)
– Also, pay attention to your problem statement and note which cycles the dryer stops too early: all? just auto dry?
– Based on your problem statement, what would be a good load of interest? In other words, which load is not operating correctly?

Your dryer may not have an LED display which would “blink” the error code to you. In this case, the buzzer will sound in time with the blinking code so you would use that to get any stored error codes. Table 1 and Table 2 explain this- read them carefully to get the idea.

The other thing to know about dryers is that the vent has a huge impact on dryer operation. A vent constructed of collapsible material, too long, plugged, stuck vent hood flapper– all these will create high back pressure and affect the dryer operation. Evaluate your dryer vent in light of this information.

[Scott Brown]

Hi George,

You’re skipping lots of steps in the Ten Step Tango and jumping right to guessing. You need to do each step of the Tango in order, no skipping.

The first thing we want to have on hand before we start troubleshooting an electrical problem is the schematic. You can’t troubleshoot electrical problems without it. That’s why a schematic review is Step 2 of the TST.

To get the schematic, we need an accurate and complete model number. This affects which schematic we pull for the job. For example, you’re missing a digit off the end of your model number. Professional techs pay very close and careful attention to the model number.

So the first thing you need to do is get the complete model number and then use that to get the schematic. Then you analyze the schematic with the problem description like a technician.

My hypothesis is that the timer is broken and needs to be replaced.

A troubleshooting hypothesis is something specific that you can test or measure with your meter. I looked on my meter and I don’t have setting for “broken” or “needs to be replaced.”

A mechanical timer has two components: the contact switches and the motor that makes the timer advance. So when you select something like a timer as your load of interest, you need to be specific about which part of the timer you are troubleshooting. The switches? The motor? And then formulate your hypothesis accordingly.

Your homework:
– Review the Ten Step Tango
– get the schematic for the dryer you’re troubleshooting

[Scott Brown]

the liquid refrigerant converts to a gas within the coils but the refrigerant gets colder?

Actually, no. It takes energy to make a liquid boil and change to a gas. In a refrigeration system, this added energy from comes from the heat outside the evaporator tubing. The liquid refrigerant absorbs this energy and boils to a vapor. This boiling is exactly the same physical process as boiling water except it takes place at lower temperatures and pressures.

When you add energy to something, you increase it’s heat content. The heat required to change as liquid to a gas is called “latent heat.” It’s called that because you can’t feel it but it’s real heat nonetheless. The heat we can feel is called “sensible heat.”

So what’s actually happening is that as the liquid refrigerant boils, its latent heat increases (because it absorbed energy from outside the evaporator tubing) while, at the exact same time, the sensible heat of the tubing decreases.

The liquid refrigerant boils at such low temperatures because of 1) the chemical properties of the refrigerant (designed to take less energy than water to make the refrigerant molecules leave the liquid and because a vapor) and 2) the pressures are deliberately manipulated (by the design of the sealed system) to allow the refrigerant to boil at low temperatures and, in doing so, absorb heat from the environment (evaporator tubes) causing the evaporator tubes to give up heat and get cold.

So, bottom line is that the premise of your question is incorrect: the refrigerant does not get colder when it boils– it gets warmer. And in doing so, the evaporator tubes get colder.

[Scott Brown]

I would suggest you to add some note there on this wrong voltage tested because students can get confused by this

Good suggestion – Done!

Also is open neutral more of a possibility than open Line ,so you’re saying OPEN NEUTRAL?

I would say that, in my experience, it is more common. Open Neutrals are also what trips techs up. Think about it- if Line is open, then ghost voltage is not an issue because there will be no voltage detected at the load, no matter what sloppy or incorrect measurement technique is used to test for it.

PCMs don’t get head faked by open Lines. But even experienced techs get head faked by open Neutrals.

[Scott Brown]

you have a circuit with two loads R1 and R2 with 120 vac

Presuming you mean that the VOLTAGE SUPPLY is 120 VAC, then stated more precisely: the total VOLTAGE DROP across R1 would be 120 VAC. SInce there would be only one load in your scenario, there would be no sum.

If BOTH R1 and R2 were in the circuit AND the resistance of R1 = the resistance of R2 AND the voltage supply was 120 VAC THEN the following would be true:

– the VOLTAGE DROP across EACH R1 and R2 would be 60 VAC. Again, that’s across EACH load.

– the SUM of the VOLTAGE DROP across R1 PLUS the VOLTAGE DROP across R2 would be 120 VAC.

Technical vocabulary is precise and it’s important to use the correct terms. This also helps keep our thinking straight.

[Scott Brown]

Hi Steven,

I’ve moved your topic from the Orientation forum where you posted it to the Basic Electronics forum.

A circuit with a single load consisting of a heating element and nothing else has 12 amps of current flowing through it yet has a power supply of 0 volts and no other external influences. This circuit is?

A circuit like this does not exist in the known universe because it would be impossible to have a current flow (movement of electrons) without a voltage differential making them move.

[Scott Brown]

if the defrost heater let say was open or burnt
how did he get 120 volts to the evap fan motor ?

Excellent question, Abe! You have taken to heart all my harping about using a loading meter for all AC voltage tests- which the hapless tech mentioned in the video did not do.

I suspect he either used a voltage hall effect sensor (“light stick” or “voltage sniffer”) or had one probe on the fan bracket (which is grounded) vs. the actual Neutral wire on the fan motor. Either way, poor technique showing that he had a complete lack of understanding about the basic electricity, circuits, and the proper use of test instruments.

Here’s a video that shows what he probably did to get his misleading 120 VAC reading at the fan motor and how he should have made the measurement to avoid getting head faked.

https://www.youtube.com/embed/VfZpH2dfQ84

[Scott Brown]

the voltage drop would be R1- 120 and R2- 120

Correct!

also ..answer to # 3 ..since one load is being by-passed ..the sum of the load R1 is 240

Correct again, great job!

Now go kick some butt on that mid-term! 😀

[Scott Brown]

7. Let’s say we’re given that the resistance of R1 = R2. If switch S1 were to open, what is the voltage drop across R1 and R2? (hint: you don’t need a calculator!)

Just realized the wording of this question could have been a bit clearer. I’m asking what are the individual voltage drops across each R1 and R2. I can see where you may have interpreted the question to ask for the total voltage drop across both loads together. Hope that helps!

[Scott Brown]

3) R1= 120

You correctly identified the power supply as 240 VAC. You also correctly identified that there is only one load in the circuit with S1 closed. In your opening post, you also indicated that you are familiar with Kitrchoff’s Law. What does Kirchoff’s Law say about the sum of the voltage drops in a circuit?

4) R2= 0 ( shunt cancels out load )

Correct answer but a slight adjustment to your parenthetical statement. Stated more accurately, shunts do not cancel out a load– a shunt bypasses a load. But I think you have the gist.

5) Parallel

It looks like parallel circuits but this is a special case because it’s a shunt. In parallel circuits, current travels in all circuit paths in parallel with each other. In a shunt, current only travels in only one path: through the shunt; the load is completely bypassed.

7) 240

Again, Kirchoff’s Law. How can each load drop 240 VAC if the total supply voltage is only 240 VAC to begin with? Can’t create more voltage out of thin air!

wow …this is very confusing ….

It may seem that way but you’re mostly there. You just need to dial in a few concepts. Circuits operate according to specific rules all defined by simple math. Although it may seem confusing at first, they’re really not. But they are exacting and require clear thinking for proper analysis. Keep at it, you’re doing fine.

In your reply, feel free to use the B-QUOTE button in the editor (as I have) to make it very clear which part of my reply you are responding to. I copy a snippet of your text, paste it in the editor, highlight it again and then click the B-QUOTE button. This puts some code around the quoted text so it shows up differently and makes it easy to follow.

[Scott Brown]

Hi Boyd,

I can’t answer this question as phrased without giving away the answer to the exam question. So I’ve re-written your question so it’s more general and I’ve also re-titled your post. Your thinking (as re-written above) is correct!

[Scott Brown]

Hi Brad,

Obviously, we can’t give you the answer to the midterm question here on the forum as that is not an appropriate use of the student forums (and would spoil the fun for other students!). But I can tell you that your analysis of the circuit is incorrect. So let’s look at another circuit and I’ll ask you some questions about it that may guide you in your thinking:

Looking at the sketch above, please answer the following questions:

1. What is the supply voltage for this circuit (not the voltage drop!)?

2. With switch, S1, closed (as shown), how many loads are in the circuit?

3. With switch, S1, closed (as shown), what is the voltage drop across load, R1? (hint: you do not need a calculator!)

4. With switch, S1, closed (as shown), what is the voltage drop across load, R2? (hint: you do not need a calculator!)

5. With switch, S1, closed (as shown) what is the circuit configuration of S1 and R2 called?

6. How many loads would be in the circuit if S1 were to open?

7. Let’s say we’re given that the resistance of R1 = R2. If switch S1 were to open, what is the voltage drop across R1 and R2? (hint: you don’t need a calculator!)

[Scott Brown]

if there was no humming heard, would it be correct in assuming that power wasn’t getting to the high run winding of the motor either?

Generally, the absence of any hum at all from the motor with power applied and when it should be running would mean there’s no power to either the run or start winding.

If either winding was getting power, but not both, then the motor would hum but be unable to start.

[Scott Brown]

I crimp on 1/4″ male spade connectors. Then I have a set of jumper wires with a 1/4″ female terminal on one to to connect to it with common terminal connections crimped on the other end such as:

1/4″ female
3/16″ female

I also use jumper wires with alligator jaws at both ends that can be rigged to connect to just about anything.

[Scott Brown]

I have no idea what those 2 capitalized terms mean. Will you be explaining them later?

Yes, in the motors module.

The point of this video to explain the troubleshooting thought process. That’s what you want to be focusing on and taking away from the video at point in the course.

[Author]

Posts