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Hi, looking for help with my Miele KFN8762 fridge freezer. For the last three years, every six months the fridge temperature begins to rise (3c normally up to 8/9/10+) and I’ve become familiar with simply giving the whole thing a 24 hour defrost. First the fridge temperature rises and then the freezer loses temperature from -18 up. There is always an iceberg on the freezer evaporator so I remove the plastic cover to give it a good thawing out. Then I usually put it back together and then it’s good for another 6 months or so. So this happened approximately 3 weeks ago. 11 days later the same issue happened, rising fridge temperature to 9/10c which I thought unusual. Initially I suspected the defrost heater element and found a donor fridge to poach bits off to make mine good. There was just a small amount of ice this time mostly around the top of the evaporator and the drain, I thawed it out, and fitted the element. I also cleared the drain thinking it might be blocked. The temperature was ok for about 4-5 days, holding the freezer at -18c and now the fridge is rising again to 7/8/9c when the door is opened no more often than usual to do a meal. It also seems to take ages to come back down to 3C. The compressor does feel hot to touch but after the temperatures have settled again it will cut out. Ie not running continually. I checked the freezer evaporator again this time and it wasn’t iced up at all. The fridge and freezer drains are all clear. Is it the fridge sensor playing up (which one there are 2?)? Or could it have lost some refrigerant? Can anyone point me in the right direction?
Evaporator sensor brings on the fan when coil reaches around -20c and then also terminates the defrost around 10c, is the fan running ? quick look on opening the door should see blades slowing down, is the thermal fuse OK ? it is a one time use fuse that shuts the heater off around +83c if a fault occurs from the coil getting too hot, is the drain cap above the compressor clean, remove and check ensuring the seal is inserted as it was on removal for inspection.
Hi Tony, Both the fridge and freezer fans are running and slowing down when I open each door. Not absolutely every time though. I assume the thermal fuse is the red small square component that screws to the evaporator casing and is inline as part of the Defrost element assembly. Before fitting the element which was a fiddly task in itself, I checked the resistance at the connector. Somewhere on the internet it said it should be 200-300ohms and mine fitted at time was 400ohms. I measured the used one I took off another machine at about 300ohms so fitted it to mine. Being a bit novice I assume that means there’s also continuity’ and hence the fuse hasn’t blown?! All i did with the freezer drain plug was poke it clear with my screwdriver. I could see my screwdriver poking through above the compressor. It seems like a black rubber nipple of a sort. Should I really remove it to clean it properly then? The fridge is currently at 9c but I’m asking it to be 3C. The freezer is exactly as I ask at -18c.
Its sometimes difficult to diagnose a fault without being in front of it for us, as we would be checking temperatures at the various sensors and then checking their resistance to confirm they are reading OK and sending that information to the board.
The air sensor in the fridge generates the fridge display and turns the compressor off at the correct temperature and switches the solenoid valve to freezer gas flow only, the fridge evaporator sensor switches the valve back and turns compressor on after the fridge evaporator has defrosted, Same with freezer sensors, air generates display and cuts off compressor and the evaporator starts the fan ( with door shut ) at around -20 to -25c and during defrosts ends it when coil is defrosted at around +10c.
The black nipple is a drain valve, which opens slightly to allow the freezer defrost water to dribble out, and then closes causing an air tight seal in the drain. It maybe worth cleaning the valve or fitting a new one if it is allowing air to enter the freezer, causing ice to form in the drain and can lead to excessive ice in the drain channel below the freezer coil from the defrost water and builds up to the bottom of the coil, this stops fan airflow and then this could cause the top of the coil to frost up with snowy ice, which the normal action of the heater can not remove.
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