Hotpoint Mistral FF92S Fridge Freezer not cooling

[radaronse]

Hi there, this is my first post. I wonder if anyone could help me out please.

My Hotpoint Mistral FF92S Fridge Freezer is not cooling. The fridge temperature is +21, and the Freezer is -13. It sounds as if it is on with power to it, and the light in the fridge comes on and off as usual if you open the fridge door.

I have read a number of posts in these forums mentioning potentially faulty thermistors, but I cannot find any information on how to locate them? I can’t see how to get in from the back, so do you have to go into the freezer, and somehow remove the rear inside panel? I have yet to look as I don’t want to keep the freezer door open unless I have to, as I have a lot of food in there.

I hope someone will be able to point me in the right direction to troubleshoot this. Thank you.

[electrofix]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

these may be frost free but they can still ice up.

the way these work is to bring some cold air out of the freezer into the fridge to cool it down. if the ducts are blocked it fails

empty and defrost completely before you assume its anything else

Dave

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

Thanks Dave, I will give that a try and post back with the outcome.

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

The fridge freezer has been turned off for just over 24 hours to defrost (food emptied, and with doors open). It has now been turned on for about 30 minutes. The temperature of each zone when I turned it on was +24 Fridge, and +24 Freezer. Now after 30 minutes it is +24 Fridge, and +8 Freezer.

Obviously it will take some time to get down to the low temperatures, but I am concerned that the fridge temperature has not changed.

Perhaps foolishly, before I turned it on, I found the rear inside cover and removed it, so that when I turned it on I could see if the fan worked. The fan came on for a few seconds and then turned off. Next I put the cover back on, but I decided not to turn off the fridge freezer while I was doing this (as I’ve read that it can cause problems if it is turned on and off and back on in a short amount of time). It took 5-10 minutes to put the cover back on and get the door shut, and i noticed during this time that frost was now developing on some of the metal pipes. I am not sure if this is normal, or if I caused this by having the fridge freezer on with the door open (in hot/humid weather). I am concerned that I have now undone any good done by the 24 hour defrost.

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

Just an update…

The temperatures are now +25 Fridge and -13 Freezer. The freezer did go as low as -15, but came back up to -13. It hasn’t got any cooler for the past 2 hours (approx).

Is there anything else I could do?

Thanks. 🙂

[feefifofum]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

radaronse wrote:
Is there anything else I could do?

I’ve recently been doing some discovery with this model and detailed it in a couple of other threads:

“Hotpoint Mistral (FF92) mis-reading temperature?“
“Hotpoint Mistral FF91, freezer only reaches -9°C any ideas?“

In that latter thread check out my post entitled “Hotpoint Mistral temperatures and resistances” (Fri Aug 02, 2013 6:30 pm ) which describes how I discovered a thermistor positioning problem caused high temperature issues.

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

Hello feefifofum. Thanks for your reply.

I have previously read some of your posts with keen interest. I am not sure if these are the same ones or different, but I will gladly take a look through them in detail.

Another update on the present situation…

The temperatures are now +21 Fridge, and -22 Freezer. -22 is the norm for the freezer (before the problem started), which is good. I’ll keep an eye on it, and if nothing improves with the fridge, I’ll try some testing on it tomorrow.

[feefifofum]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

radaronse wrote:The temperatures are now +21 Fridge, and -22 Freezer. -22 is the norm for the freezer (before the problem started), which is good. I’ll keep an eye on it, and if nothing improves with the fridge, I’ll try some testing on it tomorrow.

Has the compressor turned off?

Run a self-test. Turn the appliance off. Hold down the Save button and re-apply power. Allow the appliance to go through its self-test program. After about 60 seconds it should operate the evaporator fan for about 20 seconds.

Have you checked the state of the motorised baffle in the top of the fridge compartment when the freezer has reached -22? Remove the cover from the top-left of the fridge compartment around the light. Press the door-closed detection switch. Is the motorised baffle open? Can you feel frozen air coming in from the freezer? If not, and the baffle is open, is the evaporator fan in the freezer operating?

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

I wasn’t able to do the testing at the weekend, but this morning I did try the self test at power on with the Save button. After a period of time (approx 30-45 seconds) I did hear what I thought was a fan, but it was rather quiet. It turned off again shortly after, like you said it would.

The freezer temperature went up to -11 at the weekend, and has been that way ever since. You mentioned that the motorised baffle check needs to be done at -22, but I took a look at -11 just to familiarise myself with it. It looked like this:

No air was coming in from the freezer.

I am not sure about the location of the evaporater fan. I have seen a fan behind this inside rear panel when I opened it a few days ago – is this the fan you are refering to?

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

Any suggestions with regards to the fan mentioned above?

Over the past week, the freezer temperature has been going up and down from -19 up to +8. I have heard that the temperature display is not very accurate, and tested the internal temperature of the freezer with a separate thermometer. Over a period of hours with readings over 1 hour apart, the temperature display was always 10 degrees lower than the separate thermometer reading I took from the inside of the thermometer (the separate thermometer remaining inside the freezer for the entire testing process).

Given that the freezer is not supposed to cool the fridge unless the freezer itself is below -15, and that the lowest temperature display reading I have seen since the problem started is -19, the above temperature test might imply that the internal freezer temperature is not ever getting any lower than -9, and therefore will not supply cold air to the fridge.

If this assumption is correct, what would cause the freezer to not be able to cool lower than -9?

[feefifofum]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

Sorry it took me so long to get back to you on this. The 2nd photograph you show is correct – the evaporator fan is behind that panel.

Measuring temperature accurately needs a digital thermometer and it needs to be touching some surface. I always stick the probe through the grill that has the freezer thermistor behind so they both should indicate similar temperatures.

I’ve found that the free air temperatue is often a lot warmer than the surfaces or the thermistors indicate, which makes sense.

As to the fluxtuations I’m still working on fixing our FF92 permanently. Yesterday, after a week of behaving correctly, I caught it when it went wrong again. Evaporator showed -39C, freezer -15C and fridge +18C.

This was caused by the evaporator fan not running and therefore the cold air not being circulated.

The cause is on the control PCB. The evaporator fan (pin 1 – rearmost – on the right-side 6-pin edge connector is connected in series to the positive thermal coefficient resistor (thermistor). This is a small grey-blue coin-like device about 8mm diameter on wire legs about 8mm long.

The voltage on the output (fan-side – rearmost leg) was ~7V whilst the input was 240V. The PTC was always very overheated – probably 50C or more.

Until I can replace it I’ve simply hot-wired it by wrapping a short length of 5 amp fuse-wire around its legs so it is bypassed.

I’m currently confirming the specification of the PTC and am planning on creating a kit of replacement thermistors that others can source themselves for less than £5, instead of the ridiculous £15 each that espares et al. charge.

[radaronse]

Re: Hotpoint Mistral FF92S Fridge Freezer not cooling

Thank you for the reply. Sorry I haven’t checked back for a while.

This is very interesting, and makes sense. I would be quite interested in hearing about your kit for replacement parts that might solve this issue.

[Author]

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