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BEKO TFF577, runs OK for a couple of months before eventually the evaporator is completely jammed with ice requiring some diss-assembly of plastics and manual defrost.
I have replaced:
- main control PCB (4360620385)
- temperature control PCB (4360635285, which is a variable resistor plus pass-through connectivity for I think the air temperature sensor mounted at the evaporator air inlet)
However, problem persists. It’s not clear to me:
- If there’s a defrost heater, how this is wired or accessed
- If there’s a separate defrost stat.
Any help, wiring diagram, or exploded view would be greatly appreciated. Also how to remove the evaporator plastic cover, as it appears the whole evaporator is attached and moves with it.
Oddly and, it took me a few mins to work this out, the complete evaporator unit at the top is sold as one complete assembly that you can’t split down.
So the heater and any stats in there one or around the evaporator you can’t get as a spare part. 🙁
K.
Wow, not a very environmentally friendly design then. Thank you.
Oddly it looks like it has partially defrosted this morning. Maybe the defrost cycle is simply too short and over time the problem compounds.
Next step crash-course on Amtel MCU coding…
Mostly for the benefit of the search:
As suspected, the wiring defrost stat is connected via the PCB behind the temperature control knob. Therefore, the sensor can be tested easily from this point without cutting anything with the aid of a couple of sewing pins (and obviously a multimeter then connected to them, to read the measured resistance across the sensor):
[IMG2=JSON]{“width”:”400″,”height”:”343″,”data-align”:”none”,”data-size”:”full”,”src”:”https://i.postimg.cc/vm1rtGCG/Screenshot-2020-05-07-at-20-24-43.png”}[/IMG2]
The stat *can* be replaced, it’s mounted behind the air inlet at the top and the correct part is 4394720185. There is no cable slack whatsoever. Therefore, the old sensor needs to be cut as close to it as possible, to leave enough cable left to strip back to solder to. The full loop mounting clip also needs to be cut as the replacement sensor is a little larger due to the heat shrink and the flat end of the heat shrink also needs trimming a little:
[IMG2=JSON]{“width”:”400″,”height”:”296″,”data-align”:”none”,”data-size”:”full”,”src”:”https://i.postimg.cc/wT7jv3Nx/Screenshot-2020-05-07-at-20-24-18.png”}[/IMG2]
Having replaced the stat, the defrost is again working but it still doesn’t fully clear the evaporator, especially at one side.
Because of the connection behind the control knob, it seems doable to add a resistor inline to the sensor to bring it back in to spec and/or alter the defrost profile. The PCB does nothing whatsoever except provide a connection to it. I intend to add maybe 4k7 resistor inline and see that helps… the resistance of the sensor reduces as temperature increases, therefore adding some resistance will make the controller think the evaporator is colder than it is, hence extending the defrost cycle (hopefully).
Another update for the benefit of the search: the freezer was continuing to frost up. Seems to be a design flaw for frequent use, the defrost cycle is simply too short and the problem compounds. The accessible sensor is the air temperature sensor, whilst the defrost sensor is buried somewhere in the evaporator and inaccessible (as noted in post 2).
However, this is easy to fix for almost no money!
The control PCB is mounted in a section at the top in the back and can be accessed by removing one screw from the plastic cover. Warning: this PCB contains exposed live mains terminals! Unplug the freezer before opening and testing this.
The pinout is as follows and known-good multimeter test values:
[TABLE=”border: 0, cellpadding: 0, cellspacing: 0″]
[TR]
[TD=”width: 87″]Main PCB[/TD]
[TD=”width: 87″]Colour[/TD]
[TD=”width: 136″]Description[/TD]
[TD=”width: 87″]Good Reading (at -18*C)[/TD]
[TD=”width: 87″]Notes[/TD]
[/TR]
[TR]
[TD]KN1[/TD]
[TD]Blue[/TD]
[TD]Supply Neutral[/TD]
[TD] [/TD]
[TD] [/TD]
[/TR]
[TR]
[TD](Mains)[/TD]
[TD]Brown[/TD]
[TD]Supply Live[/TD]
[TD] [/TD]
[TD] [/TD]
[/TR]
[TR]
[TD] [/TD]
[TD]Yellow[/TD]
[TD]Defrost heaters[/TD]
[TD]300R[/TD]
[TD]Test to neutral[/TD]
[/TR]
[TR]
[TD] [/TD]
[TD]Black[/TD]
[TD]Compressor/Fan[/TD]
[TD]20R[/TD]
[TD]Test to neutral[/TD]
[/TR]
[TR]
[TD] [/TD]
[TD] [/TD]
[TD] [/TD]
[TD] [/TD]
[TD] [/TD]
[/TR]
[TR]
[TD]KN2[/TD]
[TD]Blue/White[/TD]
[TD]Dial[/TD]
[TD]30k[/TD]
[TD](position 2)[/TD]
[/TR]
[TR]
[TD](Sensors)[/TD]
[TD]Red[/TD]
[TD]Intake NTC Sensor[/TD]
[TD]30k[/TD]
[TD](-18*C)[/TD]
[/TR]
[TR]
[TD] [/TD]
[TD]Black[/TD]
[TD=”colspan: 2″]Dial/Intake Common[/TD]
[TD] [/TD]
[/TR]
[TR]
[TD] [/TD]
[TD]Brown[/TD]
[TD]Defrost NTC Sensor[/TD]
[TD]30k[/TD]
[TD](-18*C)[/TD]
[/TR]
[TR]
[TD] [/TD]
[TD]Yellow[/TD]
[TD]Deftost Common[/TD]
[TD] [/TD]
[TD] [/TD]
[/TR]
[/TABLE]
The defrost heater can be tested by checking resistance across yellow and blue on KN1. Should be about 300R, giving 180W defrost heater power.The defrost stat can be checked, should read about 30k with the freezer at normal -18*C state, by checking across KN2 brown and yellow.
To extend the defrost time, we need to make the control board think the stat is colder than it is. Since it’s a negative coefficient sensor, all we need to do is add a series resistor. I’ve found 4k7 works perfectly (1/4w is fine) – total cost about 1p. This can be added to either brown or yellow on KN2 by cutting one of those wires and adding inline, either soldered and heat-shrinked or other suitable connection method, I used some phone cable jelly crimps for simplicity:
Result is a full defrost and a completely clear evaporator after a week of operation 🙂
Unfortunately I can’t upload the image (60KB) as I don’t have enough quota left. But anyway it’s super simple, one resistor cut in to a wire.
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