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Hello,
UK whitegoods were kind enough to explain Miele’s policy on parts and third party repairs.
Not sure then that anyone here will be able to help, but just in case anyone does know….any help appreciated!
We have a Miele KFN12923 index 20-164 fridge freezer.
The compressor works, but the fridge has stopped cooling.
the freezer was cold, but iced up with a lot of ice around the evaporator.
Is this likely to be due to one of the temperature sensors having failed?
If so, is it easy enough to know which one to replace, and which one should I buy for this unit?
Many thanks for your help.
Michael.
Hi Michael
Probably not a sensor problem, the sensors are difficult to test on this unit as the connections are in the pcb housing at the rear of the cabinet, bottom left.
Your issue could be as simple as the freezer drain has blocked with ice and restricted the fans airflow and causing the rest of the coil to then over ice.
If the freezer is found to be not getting to temperature, due to over icing the fridge section cooling is shut off untill the freezer regains correct temp, but wont happen untill the freezer coil is completley defrosted along with the drain.
Turn the unit off for several days with the freezer door open, of course without knowing the amount of ice that needs to melt, it could need a longer off period.
Tony.Tony,
so grateful for your helpful advice: I think you are probably right. I took the white plastic cover off the back of the freezer compartment, and the evaporator coil was heavily iced up. It is at my son’s flat, so it has been left for a few days to completely defrost. I think I will reassemble it and see how it goes.
It is in theory a “frost free” unit, but perhaps we shouldn’t take that completely literally.
You are definitely right about testing the sensors. For anyone interested in this now pretty old model, the main PCB is fitted horizontally at the bottom RHS of the unit [looking from the rear], next to the compressor. The sensor wires run through the back wall down the back behind the condenser. They disappear behind a plastic moulding, where they go over the top of the main pcb and plug in at the back. it is hard to see which is which as they are all white insulated wires. You have to remove a plastic cover from the PCB enclosure, take off a perspex splash cover, unplug some power wire plugs from the from edge of the PCB, and then you can slide it forwards until you can get to the thermistor wire plugs at the back. The plugs are pretty small so its not easy to get multimeter probes on the connectors.
As far as I can see there is
1. an air sensor in the fridge behind a small screw on cover: there is red marking on the wire at the head end and the plug and edge of the PCB are marked red. This read 6.33 k Ohm at room temperature [20 C?] and 13.9 k Ohm with the head dangling in a cup of ice water [~0C]
2. an air sensor in the freezer compartment on the back wall, no marking on the wire or plug, marked whit on the PCB, read 6.59 k ohm at room temp and 12.95 k Ohm in ice water
3. A freezer sensor with a green marked plug at the PCB, PCB edge marked green, reads 8.16 k Ohm at RT, could not get the head in ice water
4. A freezer sensor with a black marked plug at the PCB, PCB marked black, reads 6.59 k Ohm at RT, could not get the head in ice water.
So I THINK the thermistors I can see are NTC rated 4.7 k Ohm at 25 C, and guess they behave more or less as they should in my crude test, except for the one marked green.
I THINK that the sensors I cant really get to [Black and Green] are a thermistor in the evaporator coil, and a very small PCB fixed at the top front of the freezer compartment in a duct that runs from where the fan is to a grill just inside the door. possibilities are that the thermistor in the coil is the one that reads 8.16 kOhm at RT and it has gone bad and isn’t controlling defrosting properly, OR that it is the small PCB that reads 8.16 k Ohm, and that this is nothing to worry about as it is a different kettle of fish to the other thermistors. I am guessing obviously. I could look further, say do continuity tests on the wires an get the little PCB out, but I ran out of time.
I have written all this down as I spent quite a while ferreting about with wires and so on, and it may just be of help to someone.
I am going to do as Tony suggests, totally defrost, put it all back together, and see how it goes. If it ices up again in a ridiculously short time, I will maybe investigate more. If I find out more, I intend to update here FWIW.
Michael.
Well done Michael for getting as far as you did with accessing the sensor connections, the green sensor is foamed into the rear wall of the fridge and is the evaporator sensor, the red is the fridge air sensor. The white one is the freezer air sensor that clips to the rear wall panel, the black is the freezer evaporator sensor pushed into the bottom of the freezer evaporator coil, there is also a temperature fuse behind the foam insulation at the left which acts purely as a one time blow at around 83c in the event of overheat, all the sensors are as you state 4.7 khOm and should be tested with a thermometer when checking resistance.
Resistance readings are 25c = 4.7k, 20c = 5.9k, 15c = 7.3k and at 0c = 15.3k.
The sensors are all the same with the exception of the fridge evaporator which requires a kit to replace it due to it being foamed in.
Providing the icing was not caused by a blocked freezer drain or the door left slightly ajar or an issue with the heater or blown thermal fuse the the freezer evaporator sensor which you advise was reading 8.6khOm indicates a temperature reading of around 17c and appears OK, this sensor terminates the defrost cycle and then actvates the freezer fan with door closed once the coil has reached between -20 to -25c.
Tony.
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