Evaporator fan not working – Hotpoint Mistral F/F FF71S

[very_hot_point]

Hello all,

New member, first post and all that… From reading all the other Mistral posts it looks like I’m lucky to have had one of these f/f freezers that was bought in Feb 2000 and until now hasn’t gone wrong!

I have the usual ‘evaporator fan not blowing’ problem. Have done a full defrost, which didn’t make a difference – but after which I noticed that there must have been at some point (whether recently or not) a large buildup of ice on the evaporator, as it had actually forced the metal drip tray to which the heater coil is attached a couple of cm out of its recess (i.e. away from the back of the freezer) on the right hand side. Before defrosting I also saw sheet ice on the polystyrene backing to the freezer compartment, which turned out to be saturated with water. Normal or not?

Also on the right hand side there is some flexible white cabling that is glued onto the bottom reverse side of the aluminium panel in several loops before returning back to the large white connector plug. (I’m not referring to either the thermal fuses or the heater coils).

My question is, what does this loop of thin cable do? I assume it isn’t a thermistor like the other two green / yellow thermistors in the freezer compartment that are frequently discussed? At one point along the cable loop there is a black bulge which may contain a resistor of some sort. Is it a plain and simple thermostat (i.e. on or off) and something to do with the defrost process? Only I ran the freezer without it and it still seemed to go through a defrost cycle.

I ask as some of the cable loops have come free from where they’re glued to the back of the aluminium panel, probably due to ice in the past. Can I just superglue them back on or do I need special glue – ie is the contact with the aluminium plate sensitive to what is being measured? There are also a few black marks along the wire (which may not be anything sinister as I do still get a resistance reading from it, although it never changes: 2.9 kiloOhms even when the freezer is at its coldest?)

I checked the thermistors and the yellow (evaporator) thermistor was consistently ½ – 1 kiloOhms lower than the green (freezer) thermistor as the readings increased with temperature dropping to -16 degrees C. Then suddenly the yellow thermistor dropped from 18 kiloOhms to 9 kiloOhms – and then only got up to 11 kilo ohms by -24 degrees. Meanwhile the green thermistor had reached 36 kiloOhms by that temperature.

I assumed this meant the yellow thermistor had packed in as the resistance / temp should be a smooth curve? So I swapped them around in their sockets just to see if I could get the evaporator fan to start based on the reading from the green thermistor (this is probably my downfall but I do like to experiment, often at my cost!). Of course the freezer temperature reading on the control panel (now being taken from the yellow thermistor) was significantly higher than it should be according to my digital thermometer – so the readings were probably never right for the fan to start.

I’ve now swapped the two thermistors back again, and the strange thing is the freezer temperature reading is little different to when it was being taken from the yellow thermistor – i.e. it barely goes below zero even though my digital thermometer shows the freezer is still cooling properly.

No change to the evaporator fan – it does work (when tested on 240v AC mains), but ever since the problems started it only spins up briefly when you first turn the appliance on or open the fridge door and nothing more. The fridge door switch is operating correctly.

So, some questions:
– What is this loop of cable glued onto the aluminium panel, and do I need to fix it?
– Has the green thermistor been damaged as well as the yellow one and does this point to the PCB being at fault – or were they not actually swappable and that was what affected the green one? If so, more fool me as I notice the green ones are currently out of stock, D’OH!
– I read another thread about someone changing the thermistors to no effect, but then replacing what appeared to be a perfectly good evaporator fan with another actually cured it. Why is this?

Thanks in advance for any helpful posts!

[very_hot_point]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

A picture paints a thousand words… (and I’m sorry there were at least a thousand words above!!)

This is what I meant by the yellow resistor looking like it’s failed – or is it meant to have this temperature profile?

But before I go to the trouble of replacing it, can anyone help me identify what this wire loop does and whether it is critical that it is all glued securely to the back of the aluminium plate?

[kwatt]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

That’s a defrost heater.

K.

[very_hot_point]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

Ah, good – that helps, thanks very much. That explains why I was getting a constant 2.9 kiloOhms reading from it (when unplugged) at whatever temperature!

However I assume it doesn’t do the bulk of the heating – there is a much larger diameter metal tube into which wires go and which is integrated around the evaporator coils in the normal fashion (in fact you can see the stains from it in the photo above).

This bigger heater still worked (ie. it was hot to the touch) even when the plate and wiring above was removed.

So is the above some sort of secondary heater? Should I try to glue the wires firmly back on to the metal film with some sort of heat resistant glue or is it really not important?

Thanks…

[kwatt]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

Yes, drain heater by the looks of it and yes, it needs to be fixed to the film to work correctly.

K.

[very_hot_point]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

Ah that makes sense – to stop the drain hole being blocked with ice…

I hope the glue between the wire and the aluminium plate isn’t conductive in any way – the wire seems to be fully sheathed in plastic from what I can see of it. So all I need is heat resistant glue and not some sort of conductive glue?

If so I’ve found some Araldite resistant from -30 to +150 in the man drawer that should do the trick?

As the freezer is now behaving more strangely than it did before (not cooling as far) I’m planning to re-check both thermistors to see if the green one is playing up as well.

kwatt – if I need a green thermistor is there a way of getting one any faster than the month delay in your parts store? Cheeky to ask I know, but a month without a fridge could be a bit of a bummer!

Thanks for taking the time to reply.

[kwatt]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

No idea what glue is used as I’ve never split one, they come as a complete spare already bonded and we don’t mess with them.

Thermistors are a nightmare for these at the moment, there are very, very low if any stocks of them available and we suspect strongly that unless Indesit find an alternative supplier that they will become obsolete soon. So, short answer is, no.

I know other suppliers have been showing them as stock but I have heard that, when they have been ordered, they all of a sudden aren’t.

For almost all of us, if Indesit don’t have them, nobody does unless they happen to have some on the shelf and when they’re gone, they’re gone.

K.

[very_hot_point]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

OK well fortunately I don’t think anything sinister’s happened since I swapped the thermistors round, but it had me going for a bit yesterday!

I pulled them out so that they are dangling freely and I can now still get a -22 reading from the freezer as before. I suspect from the above readings that the yellow thermistor has gone though – and the perceived wisdom seems to be that you replace the green and yellow as a pair anyway and just cross fingers!

Fortunately found one website after about an hour of hunting that did have 1 green one left in stock. So looking forward to getting this fixed, hopefully, on Friday! In the meantime I’ll only put a few drops of glue to secure the drain heater wire back on, in case it’s the wrong sort of glue and I have to redo it later.

Grateful for your help and only sorry not to have been able to buy parts from your site. I suspect if this doesn’t work my patience will have gone and it’ll be a new freezer!

[Footman2]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

The fan will not work while you have the cover off or the doors open. It will come on for about 5 seconds when the power is switched on only in that state. Before you go to the trouble of replacing thermistors just allow enough time for any ice inside the duct tube from the freezer to the fridge to melt. This build up prevents cold air from being pushed up into the fridge from the freezer by the fan. This cannot work while you have covers off or the doors open of course. You can use a hair dryer to speed things up. Often the time taken to replace a thermistor is enough for the ice to melt and there you go thinking you have fixed the problem.

[very_hot_point]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

Thanks footman2 – I forgot to mention that I did poke some flexible wire down both tubes and didn’t encounter anything. It hasn’t been operational for over a week now and that has included long periods where I’ve left it to defrost with no power. I think I’m in the right area judging by the numerous posts about thermistor trouble with this model – but accept new
thermistors may not cure it! Fingers crossed.

Would still be grateful to hear from anyone who knows if the yellow thermistor is meant to have the temperature profile above? I can of course always compare with the new one when it arrives. 😆 😆

[very_hot_point]

Re: Evaporator fan not working – Hotpoint Mistral F/F FF71S

Good news all… One less hotpoint on the scrap heap!

It seems to have been the yellow evaporator thermistor as the new one that arrived didn’t have anything like the temperature profile I posted above (it was just a curve like the green thermistor). Worthy of note for anyone else testing theirs in future 😉

I replaced both thermistors as a pair just to be safe. I also glued the defrost drip tray heater wires fully back onto the rear of the aluminium plate using Araldite that was good from -30 to +150C. The first difference I noticed was that the refrigerant pump didn’t come on straight away when I powered it up, but instead the drip tray heater went through a 10 minute defrost cycle. Evaporator fan reactivated at about -15C. Then I knew I was in business.

This F/F was about £600 when new. I realise they’ve dropped in price since, but with the added cost of having to dispose of the duff one this was well worth repairing for £40!

Thanks for your help folks! 8)

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