Hotpoint FFP187BG – Clear Ice Buildup Problems

[sbuk_wg]

Model: Hotpoint FFP187B

Hi All, Hoping an expert might be able to provide some assistance. (I work for an engineering company but have nothing to do with white goods, so i may be a bit unclear or using the wrong terminology for which i apologise in advance)

My 10 year old Fridge/Freezer is having a few issues.. Its a frost free model, and the problem im having is a huge buildup of hard clear ice which forms in the drain tube (it appears to be an unheated hole), and freezes solid along the back of the drip ledge on the back under the evaporator/defrost heater leading to the hole, then freezes upwards and outwards.

The evaporator appears to be working perfectly (it gets freezing all over, and the freezer is -8 to -11 depending on settings in use), the defrost heater meters ok (~380ohm), and when powered with 240V heats up nicely. (see my first photo on a thermal camera), so my suspicion lies with the thermal fuse/thermistor element in there?

The first issue is im not sure exactly what kind of device it is.. I assumed a thermistor but its usually described as a thermal fuse or cutout on spares sites. Its marked 72′ 20/08 16002346300.

I believe the modern version (which I have bought along with a new defrost element) is the one shown in photo 2 attached..

Its marked TF 72C 17/15 16002346300. I notice that the new one has very shiny green potting on the back where the wires enter, where my old one is dirty green and doesnt actually appear to be sealing the wires any longer.
What is confusing me though.. is that both of them appear to meter the same. Theres 4 wires (i expected 2) as shown in the diagram, and it meters out (in room temp) around 1ohm bewtween the 2 blues, 1ohm between the 2 yellows, and open circuit between either pair of blues or yellows to either of its opposing colors.

Im also not 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} sure its installed in the correct place. The third photo I attach n here

shows the evaporator and i’ve highlighted in red the defrost element. The green square is where the TF device is currently installed, however someone did come out to look at the freezer before i decided too have a go (they couldnt figure it out), and I have a niggling feeling it used to be installed where the yellow square is marked. (I could be wrong here though).

So..

1, does my analysis of the thermal fuse/thermistor/cutoff being the issue make sense?

2, where should the thing be installed? Should it be nearer to the defrost heater? or is it meant to be measuring the evaporator getting to 72C at the top there?

3, how do i properly test the TF with the 4 wires with a meter..?

Thank you in advance.

Sam

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