Domestic fridge question

[Amateur]

Hi, I have a question about a domestic fridge freezer, but I'm wondering if anyone can give any ideas as to what's wrong please as any help, especially before Christmas(!) is much appreciated please.

I have a Liebherr fridge freezer, dual compressor, digital control panel at the top with digital LED display for the temperatures. The freezer section is pretty much separate and works perfectly set to -20C and maintains this temp constantly (VOE HVY 57AA R600a compressor).

The fridge on the other hand (VOE HVY 44AA R600a compressor) is set to 4C but varies between 4C and about 12C on a daily, but random basis. There's good ventilation to the grill at the back which is clean and when the compressor is running it seems to work correctly. I.e. the evaporator gets cold enough to freeze the condensation that forms on the panel at the back of the inside of the fridge and the fridge temp falls to 4C without problem.

My first thought was a thermistor problem, so I checked the internal temp of the fridge and that also shows a 4C - 12C variation in line with the fridge's own digital display. So the fridge's own thermistor must be working ok. So the fridge knows that it is well above 4C, but the compressor doesn't start up and remains cold to the touch.

Could there be something wring with the PTC starter attached to the compressor in that it is taking far too long to reset and hence stopping the compressor from starting? Or could there be another thermistor that is somehow preventing the fridge from running?

Any help much appreciated please!

[TERRENAS]

Nothing wrong with your fridge. Its working properly.

[Amateur]

Nothing wrong with your fridge. Its working properly.

Thanks for the reply, but are you sure? From new for several years it always maintained a solid 4C, perhaps a degree or so higher if the door was opened a lot during cooking, etc but it soon went back down to 4C.

Milk / drinks, etc were always cold to drink. Only recently has it started reaching up to around 12C and stays at this high temp for hours on end. When it is at 12C, milk and drinks feel like they've been left out of the fridge for an hour or so and meat doesn't feel cold to the touch - that doesn't seem right to me and certainly wasn't how it behaved for the first few years of its life

[install monkey]

any fans inside the fridge?

[Amateur]

any fans inside the fridge?

Hi, no fans.

A bit more info:
There are 3 temp sensors coming into the control board, 1 goes to the freezer and it looks like 2 go into the fridge section, although I can't see where exactly. If I unplug them I get F1, F2 and F3 fault codes, so they are not open circuit. The temp readings for the fridge and freezer on the LED display are accurate, so I assume at least of of the 3 sensors work ok.

Do you know what the 3rd sensor would be for? Some kind of defrost monitor for the evaporator?

The control board has mains in, mains out for the light and mains outputs for the freezer and fridge compressors. I've been monitoring the live output for the fridge compressor and when the output is live, the compressor runs, so the compressor and its starter seem fine.

Something seems to be stopping the control board from sending the live to the compressor when the fridge temp gets high.

[Amateur]

* 2 of the 3 sensors work ok.

[TERRENAS]

Thanks for the reply, but are you sure? From new for several years it always maintained a solid 4C, perhaps a degree or so higher if the door was opened a lot during cooking, etc but it soon went back down to 4C.

Milk / drinks, etc were always cold to drink. Only recently has it started reaching up to around 12C and stays at this high temp for hours on end. When it is at 12C, milk and drinks feel like they've been left out of the fridge for an hour or so and meat doesn't feel cold to the touch - that doesn't seem right to me and certainly wasn't how it behaved for the first few years of its life

Fridges have a fixed cut in temperature of 11°C, one of the two sensors on the fridge compartment reads the temperature of evaporator and the other reads the ambient temperature , I guess you have a faulty evaporator sensor (not necessarily open), this is the sensor that normally control the cut in and cut out of compressor but when this sensor is faulty, the board starts automatically use the ambient sensor for that propose. And that's why now you have a fluctuate reading on display, now it display ambient temperate.

[hookster]

Have you checked the thermal protection on your compressor sounds like the safety circuit is holding off compressor start.

[NewmanRef]

Hi Amateur,

Unfortunately domestic is not my speciality, but it sounds like it could be one of two problems. What is the make of the digital control? Is there a separate control for freezer and chiller?

It could be the compressor differential setting- how many degrees above the set point temp before the compressor starts. Could this have been adjusted by dog? Cat? Kids? You when pissed?

Or sticky compressor relay on control- does the controller display a symbol to show compressor running? Often a snow flake or similar. If so, when this is displayed you should have voltage on the live out of the control. If not, dodgy relay, new control required.

[xxargs]

How is logic board powered - with small transformer and regulate circuits or using cheap capacitive divider method ???

if later alternatives - check the voltage divider capacitor have proper capacitance - if to low capacitance (wear out depend of electrical high voltage spike and so on), logic board can have very strange and non logical behavior depend of starving of power