Learn Everything About Heat Pump Defrost
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- čas přidán 9. 01. 2023
- Learn everything about heat pump defrost with this video lesson and unboxing video from Bryan and Bert. This video features the Emerson White-Rodgers Universal Heat Pump Defrost Control, and you can learn more about that defrost control at www.hvacrschool.com/wrdefrost.
Heat pumps have to operate in cooling mode to melt the ice; the reversing valve switches to send the discharge gas to the outdoor unit (as it would in cooling mode). The coil has to be colder than the ambient temperature to absorb heat from the outdoors, and there is often moisture on the coil; under those conditions, frost accumulates on the coil. A little bit of frost is to be expected, but excessive frost indicates that a heat pump's defrost cycle isn't working as it should.
Bryan and Bert force the unit into defrost, and they start off by running it in heating mode. The outdoor unit blows cool air, not hot air, in heating mode because it is absorbing heat; the reversing valve is also de-energized, and you would not pick up voltage between O and Common on the defrost board. Some units have thermostats that monitor the coil temperature; other units may use thermistors. Regardless of operating mode, the contactor must pull in, so there should be around 24v between Y and Common.
In this particular unit, a bimetallic disk will snap shut at 32 degrees Fahrenheit (0 Celsius) to initiate defrost. You can check the defrost board to see if the disk is opened or closed by checking for 24v power; if it's missing, then the disk has closed. You can jumper out the pins on the board and speed up the unit's operation to test demand defrost, but that method doesn't allow you to troubleshoot the thermostat.
The board in this video (White-Rodgers Universal Defrost Control) can be programmed to go into defrost for a maximum period of time (10 minutes, in this case) or come out of defrost at 65 degrees Fahrenheit. You can also use the board to set defrost at timed intervals (in this case, 30, 60, or 90 minutes). The speedup function on the White-Rodgers universal defrost control allows you to bypass the short-cycle delay or initiate defrost to test the board.
To initiate defrost, the board energizes the O terminal, which allows hot discharge gas to flow through the coil with frost buildup without the fans running. When the target temperature is hit, the defrost will end. While the unit is running in the equivalent of cooling mode in defrost, the defrost board also brings on the auxiliary heat strips to keep the occupants from getting cold. Some boards also have a quiet mode to make the defrost process quieter.
The Emerson White-Rodgers Universal Defrost Control replaces most single-stage defrost controls and comes with a comprehensive guide for user-friendliness and education. It also comes with two thermistors for demand defrost and a chart with the corresponding temperature and resistance readings; you can test thermistors by ohming them out and comparing them to that chart. This control also has time delays to prevent short cycling, a user-friendly and interactive display, and brownout protection.
Learn how a reversing valve works at • How a Heat Pump Revers... .
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
Good explanation good work as always
As an experienced HVAC tech, I would like to say this video is very well done. Just have a couple of things to add. I believe using sensors or thermostats to terminate a defrost cycle before its timed period is up is called defrost termination, because I know that is the term used on commercial freezers. Also, since the evaporator and condenser are constantly switched in a heat pump the better way to describe them would be indoor and outdoor coil. Also, the for the new techs out there, the first time that the unit goes into defrost after running in cooling all summer, the auxiliary heat strips that come on during a defrost cycle that temper the cold air will most probably has a small amount of dust on them that will burn off and the customer may smell it. Then when the outdoor coil comes out of defrost and the outdoor fan comes on it many times will blow out a big cloud of steam that the customer thinks is smoke. Just keep that in mind.
Nice universal board. Now they need one for two stage systems.
My rules of thumb for York heat pumps with demand defrost:
* Defrost is limited to an ambient range between 50f and -25f. Liquid line sensor temperature must be below 40f.
* Demand Defrost board uses a variable Ambient versus Liquid Line curve. Liquid Line measured with a 10k ntc thermistor located properly.
* Board will exit defrost when the liquid line temperature is 80 deg or ten minutes.
* Liquid Line and Ambient temperature thermistors are tested by disconnecting sensor wires from board and measure resistance in k ohms. Verify using a 10k NTC Resistance to Temp Chart. Should be +- 5f from actual temp of location measured.
* LL Sensor location may be wrong if previously worked on. With an outside expansion valve, the sensor should be between the valve and the coil distributor. Otherwise the defrost board may terminate defrost too early or it may not defrost at all except at six hour timed intervals. The six hour timed intervals will occur in heat mode to ensure proper oil circulation.
* 10k ntc thermistor tips: 10,000 ohms at 77f; about 32k ohms at 32f; NTC "negative temp coefficient" means Resistance goes up as Temp goes down
I don't need to go to school you teach much more than a school I have learned a lot a lot a lot ❤
Outstanding video! Your explanations and the accompanying video are very clear.
I always learn something from these guys.
Tampa Bay tech love windshield time with y'all. Thanks for sharing the knowledge
As someone who's struggled to understand the concept and functionality of a heat pump this video really made it all click for me.
Great stuff guys! Keep up the good work! Love the content.
extremely informative diagnostics very well explained thankyou.
I make it a point to explain in very little detail to the customer what to expect with their new heat pump. Condenser buzzing without the fan running, frost build up and steam are all normal. It eliminates unnecessary non billable service calls
Great video as always! Thank you guys!
Excellent video fellas, can’t wait to see y’all next week at the symposium 👍👍👍
Me too,see you all next to heat pump outdoor unit
Well done, very informative. One nice feature Trane provides for their demand defrost is a chart in Service Facts that gives you the sensor ohms but also the DC volts the board should be seeing at a particular temperature from each sensor. Saves having to ohm out the sensor in the freezing cold…a bit easier on the bare hands.
Its a great video plus you guys are doing all that with live voltage. This video is very helpful. Thanks for everything you do.
Great info. again. Thank you Bryan & Brit.
great job with the illustrations.
Your videos are always great! Up here in the Pacific Northwest defrost sensors fail all the time. They get moisture inside and can freeze and expand. The carrier sensors also have had a very bad record out of the box this year and we have replaced over two dozen of them on brand new systems.
That sounds like a manufacturing defect in the sealed component. Some good sealant should solve that problem.
I see mice and frogs shorting out or corroding the boards. In the Pacific Northwest
Great video 👍
Thank you for this video
Emerson has the best universal products in the industry!!
Awesome info thanks 🙏🙏
great video for defrost unit
Very good video guys
Great video as always
Thank you, my friend.
When I first started, those universal boards pissed me off lol I didn't understand them. Good mention of the 10k thermistors. Didn't know the charts were so easy to find.
Great video 🙌🏻🙌🏻🙌🏻🙌🏻🙌🏻🙌🏻🙌🏻keep them coming
The American Standard / Train demand defrost works quite well. Just make sure the damn coil sensor is actually attached to the coil when you install it. I had a defrost issue the first winter with my Silver 15 and when I went to test everything I found the Coil Sensor was dangling. It was like that from the factory.
Good video.
excellent explanation, however it was rather chaotic, watch it a few times and you will see some conflicting statements, would love to see a revision B of this video in a more organized format, that being said its a great video overall.
How am I supposed to wire a universal condenser motor and still have the defrost feature operate properly?
Hey Brian great video. I'd like to add 1 thing, but let me know what you think. When you have a thermister in open air I use a thermometer the same as you. Although instead of checking it against resistance I use my meter in Temperature mode and check the temperature Of the thermister. If they're within a couple of degrees of one another then that thormister Should be good. Let me know what you think?
Usually a meter will read a k type thermocouple and not a 10k ntc thermistor. What kind of meter do you have?
My defrost is operating according to specs, but as soon as the reversing valve switches over, kills the condenser fan like its supposed to, but also cuts out the compressor. I can feel the suction line heating up, so pressure is definitely building from somewhere. Any thoughts
Reads 9.7 ohms. He tells the other guy “no it’s 9700 ohms”. Then immediately reads the book and says “it’s 9.9 ohms that’s exactly what we have there.” Typical lead man response. Priceless
I'm not sure demand defrost is a good thing in a humid winter climate like SE TN. But I've not been able to find anything on the logic used for demand defrost. It has value in refrigeration and likely dry winter conditions, it seems.
One thing I don't see covered for demand defrost is that it terminates on the coil thermistor temp and the jumpers on boards, (it was a column on the WR) is to set that temp from 60-90 rather than being run time. The runtime before defrost is apparently the adaptive part but left hidden in the chip. But the termination temp is important as if you try to force defrost it will come right back out if the coil temp is above the termination temp setting. Sometimes giving the illusion of a problem with the board.
Demand defrost terminates on LL temp or time. The Emerson board is a good universal module for single stage heat pumps. Wish they had a similar version for two stage heat pumps.
Using the electric heat backfeed is not only for customer experience it also superheat the refrigerant to defrost the condenser faster correct?
In cooling mode the super heat only means that the refrigerant has been boiled off completely and has also picked up additional heat beyond its saturation temp. (think of it as water that has boiled off and then the steam is getting hotter and hotter). So in cooling mode when you have 10 degrees of SH it means that vapor refrigerant which could be at 40 degrees F has picked up an additional 10 degrees of heat making it 50f. That temp is insignificant. So anything upstream of the compressor it terms of temp would play almost absolutely zero role. It's the extreme change in pressure during the compression process(discharge) that increases the temperature significantly in order to defrost the system.
So no the heat strip is just for the customer's comfort.
When it’s 35 or lower outside my heat pump turns off and won’t turn back on until temperature outside is back to 35. So I will constantly run my heat strips for days until temp outside go back up you think my heat pump is broken?
So the compressor never turns off during the defrost cycle? When our unit cycles to defrost, the compressor stops running. The frost is staying put and that’s why I’m here.
8:25 I will respectfully disagree. I find the snap action thermostats failing (also thermistors failing) are the major cause of defrost issues. They get stuck and will not close. I've seen many encased in ice on a 15 degree day test open. If I smack them with the handle of my screwdriver, they will often close. I replace the thermostat and no more defrost issues. I also live and work in a much colder climate than Florida, maybe that's the difference.
the board drops out the yellow wire to disengage the contactor [ momentarily]
❤❤
How do ductless wall hung units that go into defrost overcome the cold outlet air temperatures into the conditioned space without back up resistance heaters ?
indoor fan should shut off while in defrost
@@mackenziegray2090 Are you sure? Standard heat pumps need the indoor fan running during defrost. Its hard to understand at times, but when the system in defrost the indoor coil it is acting as an evaporator, and it is absorbing heat while the refrigerant turns from a liquid to a gas. This refrigerant vapor then goes to the outdoor unit where it is compressed and condensed, which releases heat, with the outdoor fan off to concentrate the heat in the outdoor coil and melt the frost. If the indoor fan was off during this time, the refrigerant would not pick up much heat and the defrost cycle would not work. Please let me know if a ductless system has a different arrangement.
To get ohms from kiloohms, you don’t add 1000; you multiply by 1000 - that is, shift the decimal point three places to the right.
You are correct, he just misspoke.
@@chrisdeanndavison3626:
Customarily, the video editor puts “* multiply by 1000” as correction text at the point of the error in the video.
This error was not caught.
You are so smart 👍😁
USA-ers versus metric system
If you have rolling blackouts in very cold weather, the defrost board will lose its accumulated run time due to loss of memory. Then the frost will build up so thick you will not have any usable heat in very damp conditions.
That does not make sense. The compressor will not run during the power blackout so it will not ice up during this time. It starts accumulating run time below icing conditions and will defrost every 30, 60 or 90 minutes thereafter and clears its run time memory during every defrost cycle. If you are having rolling blackouts with that short of a duration, I do not believe the unit would heat anyway and that is more of a power supply problem than a heat pump problem.
@@Howie875 I’ll try again… if your outdoor coil is frosted up and near defrost cycle, and you lose power for a short time, the defrost timer loses its memory of the run time. So when power is back on, and the frost is still there if will not defrost for another 30,60,or 90 min. You have very little heat, and if conditions are causing frost build up, it will just run, run, you may have small amount of backup heat but that won’t heat your house without the proper heat pump capacity. I have seen this many times.
@@tbone9405 Let me clarify. After the unit misses it's defrost cycle, it is true it will have some frost on it and won't work as good as it should. But as soon as it comes back on, the defrost timer starts to work because the coil is frosted over and then it will defrost on the next cycle, either 30, 60 or 90 minutes and then will work perfectly again. Just missing one defrost cycle will not add that much extra frost on the coil. The outdoor coil gets plenty of heat from the hot gas line during defrost and most systems have a defrost termination, because all the ice melts before the timed defrost is over and if you do not terminate it, you will trip the high-pressure switch because the condenser fan is off during defrost. So, it's only a 30, 60 or 90 minute period of reduced capacity. The only time I have seen frost or ice so thick that it would not respond properly to a defrost cycle is on a system that has run for many, many hours without a defrost.
@@Howie875 This is how a defrost board works on a typical heat pump. The memory is on kept by voltage from the 24 volts coming from the hvac’s transformer, which is always on. The defrost is controlled on most heat pumps with a bimetallic thermostat, located in the outdoor unit attached to to the coil, it closes about 28 to 35 degrees. Then the defrost board starts counting minutes of run time, when it reaches 30,60 or 90 depending on the pin settings, it will initiate a defrost cycle, the mechanical bimetallic thermostat will typically open at 60 degrees. If power is lost the board will not keep the count. When power returns if will start over. The frost is still there because ambient temperature is below freezing at this point. Hopefully that helps. In more moisture prone areas this is problem. Also some power companies cause this problem, when they cycle the equipment for some programs. I was stating this issue for educational purposes, as I have experienced this in my many years of service, may not be a problem in your area, but someone may have experienced it. If your goal is to have the last word, then you can have it,lol
@@tbone9405 I have a very clear understanding of a defrost cycle. I have many years' experience myself. The only time you lose your accumulated run time is when you lose complete power, and if your losing complete power often enough to continually lose your accumulated runtime and interfere with defrost then you probably won't have enough power to heat the conditioned space anyway, and that is not a heat pump problem, that is a power supply problem. A power cycling program, if wired correctly, should have no effect on the defrost memory. A correctly wired cycling device normally just cycles of the compressor by de energizing the compressor contactor, and the board should interpret this as the thermostat being normally satisfied. An incorrectly wired cycling device that opens either the hot or common from the transformer would kill the accumulated run time memory. All I am saying, respectably, is that one missed defrost cycle is a problem that will self-rectify itself at the very next defrost cycle, period. I hope we can agree on that.
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How does the board enable quiet mode on the unit 🙋🏼♂️
It stops the compressor when going into and out of defrost, waits 30 seconds, energizes the reversing valve and starts the compressor. It reduces the typical noise when operating the reversing valve with the compressor on.
@@rj.parker thank you for your explanation. Very interesting
Good training guys! Please be an example to the young bucks and wear safety glasses when you’re face is right in front of electrical cabinet 😊
Stay safe
U are ama…
Not ice, FROST!
Long live gas boilers
Ty kalos[?] team for another great video