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Refrigerator with two compressors - How do they do it?
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soldar:
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?
edy:
I'm not sure if this helps:

https://homeguides.sfgate.com/single-vs-dual-compressors-refrigerators-88472.html

It 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

soldar:
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.

soldar:
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.
Bassman59:

--- Quote from: soldar on July 29, 2019, 06:56:04 pm ---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 ...
--- End quote ---

Not 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.
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