Liebherr sensor values

[Luggsey]

I have just been given a faulty CUP es 4653 fridge freezer. Its in spotless condition and superb quality so I’m hoping to fix it!
The compressor seems fine and soon got the freezer to -12 degrees where it stopped and maintains. The fridge doesn’t cool much so I assume it uses the freezer cold to cool it?
Anyhow I pulled out the temperature sensor from the fridge and have left it hanging out the back in the warm to see if the freezer temprature drops, which it does! I’m just checking now to see if the fridge is cooling but i8assuming it will.
So before I lash out £60+ on a temperature sensor (!!!!) Can anybody help me with table values for the fitted sensor so I can check it?
Thanks very much if you can help me keep the beautiful fridge freezer away from the recycling yard!
Cheers.

[Luggsey]

Ok, this is weird, by placing the fridge sensor outside the fridge cabinet and keeping the freezer running it got to -22 degrees but the fridge is not cold?
what am I missing here?
I dont understand the process of cooling the fridge, however its done its not working!
Its an old model and I dont think it has a defrost heater unless someone can guide me?
Its a basic control system, I only see one sensor?

[Tony R]

Temperature is controlled in both sections via the evaporator sensor in the fridge, depending on set the temperature ( fridge setting only ) the correct temperature will be obtained in the freezer, the refrigeration circuit is a loop, freezer first then fridge, once fridge is cold enough the sensor shuts down the compressor and restarts the compressor for cooling after the rear wall of fridge has defrosted. If the rear wall of the fridge is not freezing and compressor running constantly, then you may have a weak compressor or a shortage of gas, the last version of this model an index 20B-001 it was produced between 2004-2006, with two earlier versions produced before this, so what ever index you have they are old units.

[Luggsey]

Thanks Tony! Is the evaporator sensor a capillary driven unit? That’s the only component I dont recognize if its a capilliry stapped around a bulb on a dead end length of pipe sticking out from the back?
Have I understood correctly the fridge only gets refrigerant once the freezer is down to temp?
So there is a capillary driven valve of some sort? There is no extra wiring there so I assume so…?
I dont really get why if I put the fridge sensor outside the cabinet the freezer can go to -22 degrees but the fridge stays cold, if it were low on gas or the compressor was weak would that happen?
Wishful thinking I suppose.
Do these capillary units fail and if so is it repairable on an old unit like this? I could spend a few quid on it rather then buy new.
cheers.

[Tony R]

The capillary tube is the thin copper pipe wound around the filter drier, This is part of the refrigeration pipework containing the refrigerant and controlling its flow. There is no valve on this unit to divert the refrigerant to one or both of the compartments. The evaporator sensor is the white cable with sensor bulb, attached to the rear interior wall of the fridge by a screwed on plastic bracket. As stated the system is a single cooling circuit supplying refrigerant cooling to freezer and fridge. If the sensor has now been placed away from the rear wall of the fridge ( evaporator ) and the fridge is now cold as per your last post, then it is possible the sensor is faulty, but you said in your first post the fridge was not cold with sensor removed, so slightly confused now. But to recap the refrigerant flows to the freezer first and once frozen around the freezer walls, it then flows to the fridge, once the fridge rear wall is frozen the sensor will shut off the compressor and the fridge wall will start to defrost, but before the freezer has a chance to also defrost the sensor brings the compressor back on and the process is repeated.

[Luggsey]

Hmm, I think it may be low refrigerant then, im sure the fridge is warming slightly which I understand can happen when its low.
I will order a gauge and clamp connector and check it, thanks for the guidance.

[Tony R]

Not recommended, the refrigerant is R600a a highly flammable gas, and mass critical for amount in system, unless qualified it is not to be messed with.

[Luggsey]

Thanks for the heads up, I qualified as an explosive atmosphere electrician (Compex) testing aviation fuel storage, haven’t gone bang yet! I will be careful. ☠

[Luggsey]

Just an update on this job, finally sourced some kit at reasonable prices to allow experimental work to determine fault. I am very careful as previously noted but would appreciate guidance?
The low side of my circuit was in vacuum so I have added some refrigerant to approximately 2 psi. (I’m only trying to prove if this unit is worth saving) and the fridge is now cooling its evaporator ok?
I do have the capacity to fully vacuum and refill by weight which I may do later but for now is there a psi value I can go by? The compressor is warm but not excessively so, the high side is hot but cool at the bottom of the condenser and the low side at the compressor is lightly frosted. I will have to see how it stabilizes after a few hours?
I’m interested to know if anybody braizes pipes on R600 units? Seems like a dangerous profession!!
If I need to permanently seal up the pipework does this require the crimping method or do you guys get out the torch?

To add, fridge cooled and thermostat shut off and restarted so looks ok?
Frosting reduced on low side now, I am supposing that was normal while the compressor was working hard to initially cool the unit from room temperature?
Is it ‘normal’ for an R600 to need a refrigerant recharge after several years use? Or should I be looking for a leak with my lighter?

More update, low side is still frosting.
Fridge temperature seems wide going from -1 to 6 degrees, is this right on an older model without auto defrost?
Seems to work ok apart from that?
May add that this could be a tropical model as it came from Australia, will that make a great deal of difference?

[fkyriazid]

Tony R wrote: ….and restarts the compressor for cooling after the rear wall of fridge has defrosted……

Hi Tony, is the evaporator sensor that is in the fridge area (behind the light) responsible for understanding that the rear wall of the fridge has defrosted? And also, is this the one responsible to turn on the compressor when temperature rises too much? Or the open/close are also dependent on other sensors or the defrost system or ?

[Tony R]

Liebherr produce hundreds of models of units and each version of a certain types operates in different ways, some use one sensor in the fridge section to control temperature and defrosting, others have two sensors in the fridge and bio fresh units have three, there are also one or two sensors in the freezer compartment, some fridge freezers are a one circuit refrigerant flow and others use a solenoid valve, so as you can appreciate without being in front of the unit and having the full factory training it is sometimes impossible to advise precisely on faults and possible remedies posted on a forum.

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