Refrigerator with two compressors - How do they do it? - Page 1
Forum section: electronics / general

author: soldar
author_rank: Super Contributor
timestamp: July 29, 2019, 06:56:04 pm
content: My refrigerator should have been replaced some time ago but I kept it until it could not keep up with the recent heat wave we had.The freezer was at -40ºC but the refrigerator part would barely go lower than 15ºC. Clear sign of needing refrigerant but the thing is not worth repairing.Of course, this is the worst moment of the year to buy a refrigerator because of all that crap about supply and demand. So I know what model I want to buy and I know how much I want to pay but in this case Supply does not meet Demand so Demand will have to wait two or three months until Supply comes to its senses in Autumn.In the meanwhile I am lucky enough to have acquired from a neighbor that was leaving and abandoned a Liebherr refrigerator, two doors, bottom freezer (I don't really care about the bottom freezer).Anyway, it works and will fill in for some weeks. I noticed it has two compressors. I always thought refrigerators with two compressors had one for the freezer and one for the refrigerator, both working independently from each other, each with their own thermostat.I can't totally confirm it but it seems this one may not work like that. It seems to have one compressor running most of the time and the other kicks in now and then. I cannot follow the refrigerant tubes as they are hidden. Maybe I can spend time trying to see what gets cold where and when.So I have a feeling the arrangement may be more like a traditional refrigerator: refrigerant evaporates in freezer first and then goes to refrigerator. Except maybe in this case the refrigerator has a second unit to help when needed.I don't know. I just thought it was two entirely separate units but now it seems it may be more compliucated than that.Does anybody know anything about this?

author: edy
author_rank: Super Contributor
timestamp: July 29, 2019, 07:12:07 pm
content: I'm not sure if this helps:https://homeguides.sfgate.com/single-vs-dual-compressors-refrigerators-88472.htmlIt sounds like there is a separate compressor for freezer and separate for refrigerator. Depending on the cooling required and number of times you are opening the doors, you may hear one compressor go on more often than the other. But it seems it is just a separate circuit through each compressor to the corresponding coil and blower, each dedicated to it's side of the unit (either to the freezer side or refrigerator side).Alternatively, it could work by two stages like this, but this is more for needing to drop the temperature really low which I am not sure if needed:And then you have this type of system which has two expansion valves to evaporator coils/fans but 1 compressor/condensor coil here, I guess to alter the flow between the 2 compartments as needed:https://aip.scitation.org/doi/pdf/10.1063/1.4968264

author: soldar
author_rank: Super Contributor
timestamp: July 29, 2019, 07:42:11 pm
content: Thanks, that's informative but I don't think it is the case.Another problem is that the refrigerator is supposed to have a sticker inside with model number and other information but the sticker is gone and I cannot find manuals or other information. I can only see the model Liebherr 35 Spezial Tropic. I believe the basic model is 35 and "Tropic" is because they make the same model for different ranges of temperatures and "tropic" is the higher one.If I search for Liebherr 35 I find some information but no model has the same panel as mine.It clearly has two separate compressors and the condenser coil in the back is clearly divided in two parts so I would guess totally separate circuits.I am beginning to think it may be defective. It is always using 100 W minimum and one compressor is very hot but the corresponding condenser coil is not warm. Hmmm, There may be a reason the neighbor left it behind.I may need to hurry up to buy the new one.I need to check if that compressor is OK or is just burning electricity. Both refrigerator and freezer have good temperatures but the power consumption is way too high.

author: soldar
author_rank: Super Contributor
timestamp: July 29, 2019, 09:53:46 pm
content: I have been investigating a bit more and, as far as I can tell, both circuits are independent but the freezer compressor seems to run, or at least use 100 W, 100% of the time. I don't think that's normal and I need to look into it more.I still wonder if there might be some link between both refrigerating systems...There's still something I don't quite understand.

author: Bassman59
author_rank: Super Contributor
timestamp: July 29, 2019, 11:09:01 pm
content: Quote from: soldar on July 29, 2019, 06:56:04 pmNot true! If the freezer is cold, then the compressor is working and it doesn't need refrigerant.Usually the cooling coils are in the freezer compartment behind a plastic cover. That cover has a small fan on it. Behind the cover near the coils you'll see a little bit of ducting that leads to the refrigerator part, and there's a mechanical damper that controls the airflow through that duct.Pull off that plastic cover -- I bet the coils are covered with frozen condensate. In that case, the air can't circulate through the coils so cold air doesn't get down to the fridge box. This is a sign that your defrost timer is not working, or the defrost heating element by the coils is not working. Both are easy and cheap repairs.You should defrost the coils with a heat gun and lea the fridge cool off for a couple of hours. I bet it'll get cold.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 29, 2019, 11:31:39 pm
content: Some "digital" refrigerators have two evaporators plumbed in series or a sectioned evaporator, the freezer evaporator right after the expansion valve. Temperature control can be shifted between the sides by adjusting fan speeds. Apparently, while the more common design of a damper to control the airflow is cheaper to make, the evaporator being cold enough for the freezer dehumidifies the refrigerator section, not so nice for fresh fruit and vegetables.As for troubleshooting, check that all the fans are in working order as well as the damper and motor driving it, if present.

author: soldar
author_rank: Super Contributor
timestamp: July 30, 2019, 06:51:27 am
content: Quote from: Bassman59 on July 29, 2019, 11:09:01 pmLet me put this mildly: you are wrong and you have no knowledge or experience in refrigeration.The first sign of any refrigeration system in need of refrigerant is that the evaporator temperature decreases because pressure decreases and yet the unit will not pump as much heat as it should. This is true in refrigerators as it is in air conditioners. An air conditioner should not make ice and if it starts making ice it is a good sign it needs refrigerant. A -40ºC temperature in the freezer is not normal, it is too low, a sign the system needs more refrigerant (and work at higher evaporator pressure). I speak from experience on all counts.Anyone with some experience, even if it is just as an owner, can tell you this. Please inform yourself. You only need to use Google.The rest of your post is also wrong so I won't address it.

author: soldar
author_rank: Super Contributor
timestamp: July 30, 2019, 06:57:11 am
content: Quote from: NiHaoMike on July 29, 2019, 11:31:39 pmNo fans anywhere. This is a conventional traditional conservative fridge.On the one hand I think it is simply two separate systems altogether, one for freezer one for refrigerator. On the other hand I am not so sure. It could be that the freezer somehow "bootstraps" with the refrigerator part as shown byedy's diagram above.

author: Nauris
author_rank: Regular Contributor
timestamp: July 30, 2019, 04:52:06 pm
content: Quote from: soldar on July 30, 2019, 06:57:11 amBut how could it bootstrap if it has two separate condenser? Maybe it has half-blocked capillary or tired compressor or something like that making it run all time? I would just disconnect wires to compressor if you don't really need that freezer.

author: soldar
author_rank: Super Contributor
timestamp: July 30, 2019, 05:29:44 pm
content: Yeah, I am confucious. My wife says to stop messing around and just buy a new fridge even if it costs more. She's probably right but, what the heck, I want to play around. She says my economies are not economies but econoshits. She's probably right but I have fun messing with things.We had the same issue over a split A/C which had lost some refrigerant and they were asking way too much to recharge. I stuck to my guns and finally got a guy to do it for about half the price. (He broke the condensate drain tube while doing it but we don't talk about that.)Regarding the fridge I am thinking if the control unit might have a stuck relay which just keeps the compressor on. Once I have another fridge I can look into it but now it is the one I have in use.Next project is going to be building an air compressor with the dead fridge compressor. I need to start planning that.发自我的华为手机

author: christopherwatkins
author_rank: Newbie
timestamp: June 10, 2020, 08:35:32 pm
content: Guys, thank you for your comments. We have a Samsung refrigerator and it often breaks, especially I am concerned that the icemaker breaks every 2 months and I am tired of fixing it. I decided we'd better spend a little more money and buy a good refrigerator. If you can recommend a good refrigerator, I will appreciate your advice. During the research, my attention was drawn to this siteianboer.com.au. I liked the characteristics of the refrigerators they have, if anyone has had experience buying an industrial refrigerator, please let me know.

author: amyk
author_rank: Super Contributor
timestamp: June 11, 2020, 02:46:15 am
content: Quote from: christopherwatkins on June 10, 2020, 08:35:32 pmThe archiac bump post will get an equally archiac recommendation: A GE Monitor Top. (Despite their age, they are actually extremely efficient. Used ones in working condition sell for astronomical amounts.)

author: Labrat101
author_rank: Unknown
timestamp: June 11, 2020, 08:12:21 pm
content: Its what is called a cascade system .were the second compressor acts as the condenser of the first stage .I have not see one of these for over 40 yrs .each system will have a different gas .in our old lab we had a freezer for testing equipment to work @ -60 c for ships working in the antarticit used B13a and R13a .B13a was a custom gas . they both have different properties and are quite difficult to set up so both systems are balanced.There are a few different gasses that these system work with .Your diagram is correct but you need a tech that works with these units .Warning be careful one stage will have R13 it is very high pressure and I believe its been banded now .I actually built a few of these sub cooling fridges in the 70 & 80 for the company I worked for .each one is custom built for the customer.I guess this freezer is not 40 yrs old .The newer fridges use R*** A butane derivative