Hotpoint Mistral warm fridge / cold freezer

[mikevernon]

My Hotpoint Mistral Plus is suffering the common problem of no cooling in the fridge but normal cooling in the freezer. The fan which circulates cold air to the fridge section is no longer running.

I’ve emptied and defrosted it, and removed the plastic plate at the rear of the freezer section. The fan blades rotate freely and there’s no sign of the motor being burnt out. I’ve unplugged both the thermistors (green and yellow plugs) and tested their resistance. One is 3.65k ohms and the other is 1.68k, and both readings fall as soon as I warm them with my fingers. I think that suggests they are both ok? Can anybody confirm?

How can I test the fan and what should I test next? I’m very reluctant to change the control module because the fridge is now quite old, but if there’s something else I can test before deciding to scrap it I’d like to try.

Any helpful suggestions would be much appreciated.

[mikevernon]

Re: Hotpoint Mistral warm fridge / cold freezer

After trawling through lots of very similar problems posted on this forum I’ve reached 3 conclusions:-

1. I don’t properly understand how this F/Freezer works

2. The majority of people posting on here know as little as I do, and often less

3. The most likely cause of the problem is a faulty yellow thermistor

Having looked at the advice page on this website I had decided that both thermistors were ok because they both showed decreasing resistance as I warmed them in my fingers (testing simply involves unplugging the plastic connector blocks and inserting the multimeter leads into the two terminals). I ignored the fact that the yellow one showed less than half the resistance of the green one, at around 1.5kohms.

I was sidetracked by the fact that I couldn’t see the evaporator fan running (the one behind the back panel in the freezer compartment, not the one at the bottom next to the compressor). I read that it doesn’t operate until the freezer temp has fallen below -15 degrees, so I ran the freezer until it reached -20, but still no fan. This made me think the fan might be faulty, or maybe the control board, but I hate the idea of diagnosis by trial and error, replacing parts until the problem goes away.

I then decided that if the yellow thermistor switches the fan on and off, I should try disconnecting it. Sure enough, with the thermistor unplugged, the fan runs. So that has convinced me that the yellow thermistor is very likely to be the problem, and since they are available on ebay for £5.99, I’ll take the risk.

If that doesn’t fix it, does anybody want a free Hotpoint Mistral Plus in green?

[mikevernon]

Re: Hotpoint Mistral warm fridge / cold freezer

Yippppeeeee!!! Success!!!

The new thermistor arrived this morning and has cured the problem, BUT I was very confused at first because the new one had exactly the same resistance as the old one at room temperature. Warming them in my fingers produced a similar drop in resistance, so at that point I very nearly gave up and took the freezer to the local tip.

But as a last resort I put both the old and new thermistors into a working freezer for 5 minutes then re-measured their resistance. And this time there was a big difference. The new one showed a resistance of around 13 kohms, but the old one had actually fallen to around 1.5 kohms, showing that it was defective at lower temperatures.

I hope my experience will help somebody else on here.

[Mikethelad]

Have the freezer working at -22 but the fridge not. I have fully defrosited and did not resolve. I have now changed the yellow thermistor and again this has not helped. Do I need to re-assemble all the panels in order to test as I have not. Also are getting a lot of condensation on the freezer door, not sure why this is

[Wirplit]

My now 20 year old but previously faultless Mistral ff 93 recently developed same problem. My fan however was fine. The problem was the defrosting system. When I took the back of the freezer off I could see the evaporator was frozen up and bad enough to block the air vent to the upper fridge part. I cleared out the ice and it worked fine again until it again the fridge started to warm and again opening up the freezer back the ice had built up again. This leads me to believe that there are 3 possible faults all relating to the defrost system.
1. The defrost heater itself is not working. 2. The timer for setting off the defrost heater at specified times to go through defrost process and start off the heater. 3. the thermostat that determines when the heater comes on or when it needs to go off?. Obviously 2 and 3 cant both control the defrost heater so I expect it is the timer and that is set to go onto defrost at specified times …but perhaps the thermostat has a part to play too.
Apparently the defrost heater can burn out and a continuity test should determine that. I will try this next.
As for the timer… well not sure even which part it is. This seems most likely cause in fact but what does part look like?
I have an exploded diagram from hotpoint https://parts.hotpoint.co.uk/category/model_ff93s/all_parts but this just has numbers 521 or 520? without descriptions. No such part is of course available there at least.
Anyone know more? Specifically about how the defrost timer operates/ where it is etc?

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