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Here’s an example that may help illustrate what Sam told you: when you drink hot coffee, you are drinking a subcooled liquid. Huh? It’s true! At atmospheric pressure, water boils at 212F. Coffee (which is mostly water, so we’ll treat it that way) is typically at 150 to 190F which is below the boiling point. Same thing going on with refrigerant. Only difference is that the pressure is engineered to be something much lower than atmospheric so the refrigerant boils at a much lower temperature, typically -20F in a freezer. And it is really boiling in the technical sense because you have a phase change from liquid to vapor going on.
Subcooling and superheating describe thermodynamic states of the refrigerant, not their temperature. We use temperature and pressure to tell us where the refrigerant is thermodynamically: saturation, subcooled, or superheated.
The case study is on Ranges and Ovens.
Oops! I had dryer on the brain.For some weird reason, I was taking about dryers. My apologies!
Let’s talk about open TCOs in OVENS and RANGES! Really the physics is very similar to open TCOs in dryers. It’s all about air flow. I go on an inop oven call and find an open TCO, I’m looking for an air flow problem, primarily cooling fan operation and flow and installation clearance specifications. On some ovens, like Dacor, cracking open the door during broil will disrupt the cooling air flow and pop the TCO (resettable in the Dacor, which was nice).
Sometimes, you don’t find anything discernibly wrong. If it’s an older installation and this is a new problem with no discernible problems with air flow, then you can chalk it up to a failed TCO. Sometimes, they just fail.
December 16, 2023 at 11:26 am in reply to: The Ideal Refrigeration Cycle vs. the Real World Cycle #25461But I thought saturation was a combination of vapor and liquid.
Saturation is expressed as a gradient of vapor present in the mixture from 0% to 100%. Refer to the P-H diagram. At 0%, you have no vapor, it’s all perfectly saturated liquid. It is said to be totally saturated with heat and can’t hold even a fraction of a BTU more. Anymore heat starts to make vapor but– here’s the trick– it absorbs heat WITHOUT any measurable rise in temperature. That’s is the miracle of saturation. At 100% saturation, you have 100% saturated vapor and 0% liquid. If you add anymore heat at this point, there’s no more liquid to absorb the heat by changing from liquid to vapor so all the heat goes to the vapor. This heat is measurable and is called superheat.
Also I thought we had super heat to ensure the compressor doesn’t get slammed with liquid.
This is correct precisely BECAUSE it’s a real world system. We idealize this for illustration purposes by saying that in an ideal system, only 100% saturated vapor goes to the compressor suction. In the real world, we can’t guarantee this because of the variations in the heat load. So we have to deliberately build in superheat to avoid slamming the compressor with liquid.
So, when we find an open TCO such as in the Case Study, is there something we should be on the look out for?
Open TCOs in dryers will almost always be caused by one of two things: 1) poor air flow or 2) grounded heating element.
Open TCOs in dryers will almost always be caused by one of two things: 1) poor air flow or 2) grounded heating element.
You should watch this workshop recording on dryer thermal controls where I explain in detail how TCOs work and what makes them blow.
Also, this blog post has good information on how to properly assess dryer exhaust air flow and compare to specs.
October 30, 2023 at 6:38 am in reply to: Pressure Switches, Thermostats, and Sensors 8.2 quiz #25395It may be helpful to unpack the meaning of the acronyms, PTC and NTC.
PTC stands for positive temperature coefficient.
NTC stands for negative temperature coefficient.
Both of these terms refer to the graph of resistance versus temperature where resistance is on the y-axis and temperature is on the x-axis.
The coefficient refers to the slope of the plotted line and is the slope coefficient “m” in the general equation, y=mx+b.
If the slope coefficient, M, is positive then the line or curve will slope upwards as you proceed along the X axis. In this case, resistance increases as temperature increases.
If the slope coefficient, M, is negative than the line or curve slopes downward, as you proceed along the X axis. In this case, resistance decreases as temperature increases.
Another way of saying this is that for negative coefficient, the y-axis and the x-axis are inversely related.
Does that help?
A common saying is, “Current takes the path of least resistance.” This is a misleading half-truth. The real truth is that electrons (“current”) takes ALL VALID PATHS simultaneously. A valid path is one that is NOT OPEN and has a complete, uninterrupted path from the power supply, through the load, and then back to the same power supply. This is why you can have parallel circuits, each with different loads of different resistance, and electrons from the power supply will go through ALL the parallel loads. The AMOUNT of electrons that goes through each load is inversely related to the resistance (really, impedance) of the loads. Loads with lower impedance will allow more electrons through.
As Susan mentioned, shunts are a special case. A SHUNT across a load DOES NOT create parallel circuits. The shunt is a path of 0 resistance (functionally speaking– ignoring the minuscule wire resistance) therefore 100% of the electrons will go through the shunt instead of the load.
is it possible to elaborate here as well?
Every circuit has to return to its source. Think about the return path for the spark circuit. What component allows the spark current to return to the “source” (ie., spark module).
Its my understanding that ions only are present with the flame.
This topic is about Module 7, Unit 3. Your question pertains to Module 7, Unit 4. Your question is amply explained in the video for Module 7, Unit 4. Please review. If still confused, please start a new topic.
September 21, 2023 at 7:30 am in reply to: Module 2 unit 4 User Interface Controls In Laundry Appliances #25308In Frigidaire terminology, yes. The middle terminals are just the part of the circuit being connected to either the top or bottom terminals to make different circuits. You’ll see this readily on the schematic.
September 18, 2023 at 9:59 am in reply to: Module 2 unit 4 User Interface Controls In Laundry Appliances #25302Good question. You would need the schematic to answer this, which I didn’t include in this video. However, this video from the Core course does show reading the the schematic in conjunction with the timer chart.
The short answer is that the middle row of contacts is from the circuit that is being switched to either the top row or the bottom row, depending on where the timer is in the cycle. But watch the above video for a more detailed explanation.
Question; would you be able to do the same testing at the board and come up with the same results or do you want to go to the actual load itself and test?
Absolutely you could (and usually should) do this exact testing from the board. The schematic shows you the wires connecting from the motor to the board. Simply follow those lines from the motor back to the board. Note the pin connections where the lines connect to the board. Those points become your test points exactly as if you were at the motor itself. Why does this work? Because when you have a wire connecting two points, the two points that are connected become EEPS– Electrically equivalent points. In other words, what you do at one end is the same as if you were doing it at the other end. This is the power of EEPS and reading schematics.
The reason I tested the motor this way was first for a demonstration. And second, because in this particular case, the refrigerator could not be pulled out from its cubby without the great peril to the floor. And the customer was already super anxious about scratching her high dollar floor.
Also, what was the initial customer complaint for the service call discussed here?
The original customer complaint was a revving noise from the fresh food compartment. This revving sound was a result of the evaporator fan motor RPMs increasing rapidly, then decreasing rapidly, then increasing rapidly, then decreasing rapidly and on, and on it, would do this throughout the day and drive her insane. I explain this later in the video. Because of the potential floor damage liability, it was very desirable in this situation to diagnose the problem without rolling the refrigerator out.
Hi Ray. I don’t have a video showing troubleshooting BLDC motors from the board. But this would be exactly like troubleshooting it at the motor itself. The only difference is that you’re using the schematic to follow the wires from the BLDC motor to the board so you can identify the pins where you’re place your probes.
For example, in this video, I’m demonstrating the voltages into and out of a BLDC evaporator fan motor that’s already removed from the refrigerator. In this particular case– GE FDBM– it was actually easier and less risky to test the voltages at the motor itself because the board was in back and pulling the fridge out risked scratching the expensive maple floor which the customer was very anxious about. The exact same tests could be run from the board by simply using the schematic to follow the lines from the motor to the board to find your test points.
If we get moisture in the sealed system we get the restriction near the end of the cap tube and it cycles on and off.
This was actually the case with some GE models several years back. Moisture was introduced into the system at the factory. It would manifest in such a way that ice would form at the capillary tube where it entered the evaporator and then form an ice plug. This would cause the evaporator to warm up which after a while would melt the ice plug and then restart the flow of refrigerant and the refrigeration process. This, in fact, is the dynamics of moisture in a sealed system.
2) Will the filter dryer need to be changed after the removal of the moisture? since if the filter dryer has to be changed and we have to do sealed system repair then it is better to open and recharge the sealed system instead of using the heat gun.
The fact that moisture was present in the system in enough concentration to cause a problem means, de facto, that the filter dryer was not able to handle the moisture. The filter dryer may have been saturated with moisture and unable to handle any additional. That additional moisture would have been circulated in the system wreaking havoc.
In such cases, you will want to certainly replace the filter dryer, but also pull a deep vacuum on the system to ensure that you have evaporated all of the residual moisture in the system. Then recharge the system, by weight, according to the manufacturer’s specifications on the model number tag.
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