Frost free upright freezer problem. Long Post

I have a Bosch full height upright freezer that is (meant to be) frost free. It has the evaporator at the top and a fan blows air around the cabinet to freezer the contents. Normally as good as good and anytime you look at the evaporator it is either completely clear or the slightest film of frost visible.

How do these things work? I assume that there is an electrical heater on the evaporator that comes on after the compressor switches off to melt the frost and the water drains away. If there is cooling demand, it either abandons the defrost if unfinished or perhaps allows it to finish and then commences cooling?

Am I on track?

The problem is that I noticed that the frost had built up seriously a few weeks back and the temperature was rising inside. We *think* that the door had got left ajar but no-one will confess to this. I then spent some time playing a hot air gun over the evaporator melted all the visible frost and after switching back on normal temperature was achieved.

But slowly over a period of weeks, the frost has been building up but the temperature has been maintained ok.

I can imagine a conflict between the defrost process and the demand for cooling. Maybe the defrost part uses a 'just above zero" temp sensor to signify frost clear and that is conflicting with the cooling cycle?

I wonder if the heating cooling algorithm can't cope with the remains of ice that I did not melt away fully and it is slowly building up again or perhaps if the heating element has failed.

In normal use (without the door being left ajar!) the only source of frost should be a bit of warm air let in when the door opens and so it does not need a huge defrost capability.

I have had one suggestion of letting the whole thing defrost naturally over a couple of days, but the trouble is that it holds the vast proportion of our frozen food stock and we would need a dedicated feeding frenzy over several weeks to empty the thing.

Thanks if you have read this far! Any suggestions please folks?

Reply to
Bob Minchin
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Two thoughts.

1 - you have a leaking door seal (or a leak elsewhere) that slowly allows moist air from the room into the freezer, or the door isn't shutting properly (BTDT etc).

2 - to defrost it, get a _large_ cardboard box and line it with sheets of polystyrene, say 1" or more thick, bottom, sides, and a panel for the top, all cut to size and close fitting. Freeze several plastic bottles of water, or get a good collection of ice packs / freezer packs, and freeze them. Put them in the box, along with the contents of the freezer. Repeat until freezer is empty, then turn freezer off, leave the door open, perhaps direct a fan heater into it set on 'low', and put plenty of old towels in the bottom and on the floor in front of it to mop up the melt-water.

The cardboard box/boxes will keep the stuff cold for long enough to allow the freezer to defrost.

Reply to
Chris Hogg

You summarised it quite well - My daughter had one (not Bosch) and I had to replace the timer as a gear had stripped I recall.

Reply to
DerbyBorn

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Reply to
DerbyBorn

This and other videos will reveal the operation:

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Reply to
DerbyBorn

If you can, take the cover off the evaporator plate and see if it is all frozen up inside. If it is, the timer could be the fault. Maybe. There should be/might be little white plastic plugs holding the cover in place.

Reply to
Mr Pounder Esquire

Thanks DB I'm not sure if mine has a timer module or if it is electronic. The badge on the front says "computer control" but that could be marketing garbage. I'll have to drag it out from the wall and see if there is a module round the back. I'll spend some time on YouTube thanks for the prompt. I should know that nearly everything appears there.

Bob

Reply to
Bob Minchin

The evaporator seems to be just tubes and fins with air blown through. I have a hunch that my hot air defrosting is just melting a little ice which then drips down onto other ice and freezes again.

I'll try looking at the control board again. It has a couple of triacs on it and I suspect they switch the fan and the heater.

If I can be certain which is the defrost heater, I might be able to power that up manually, leave the freezer loaded but switched off and accelerate the defrost process? Worth a go I reckon.

Bob

Reply to
Bob Minchin

That is what I have done to a frost free freezer a long while ago. I now avoid them.

If you can remove the rear panel inside the freezer then investigate and thaw all the ice you can see. The plastic doesn't take much heat so be careful.

Some posters have mentioned control and timer systems, but once the heat exchanger is clogged with ice, no heating (frost free) cycle seems able to clear it.

Reply to
Fredxxx

I called it a plate in error. Frost free do indeed have tubes and fins with a fan blower motor. My experience with refrigeration ended in 1999. So you did take the cover off then?

Reply to
Mr Pounder Esquire

New home fully modernised 9 years ago. There was no way a frost free fridge freezer was going in there. My conventional fridge freezer is set on Number 2 and works fine. The compressor is very quiet and does not run for too long. I am aware that the thermostat is getting to the end of its life, but I can get one from the net for about 10 quid. Dead easy to fit.

Yip.

Reply to
Mr Pounder Esquire

Yes the front cover is off exposing about 5 individual plugs, one of which I'm pretty convinced is the defrost heater having looked at pictures of replacement one. One pair of connections measures 280 ohms or about 200 watts on 240v which seems about right for the job.

Reply to
Bob Minchin

Not all frozen up then?

Reply to
Mr Pounder Esquire

Rather than carboard boxes, I have used the fridge, which is much easier and quicker than the freezer to empty by eating everything - especially if done at the right time of the week.

If there is a removeable panel in the back of the freezer, a hairdryer or a steam wallpaper stripper will soon clear any ice behind it.

Make sure that the drain is completely clear. Any ice in there will cause a continual build-up when the water from the heating cycle of the frost-free function cannot drain to the evaporation tray.

SteveW

Reply to
Steve Walker

Bob Minchin wrote in news:oqm2f6$fd1$ snipped-for-privacy@dont-email.me:

They can get overwhelmed with ice due to an "incident" and then the defrost time doesn't quite clear it. A full manual fefrost is the way to go.

Reply to
DerbyBorn

I had an old appliance which developed bad contacts on the mechanical time switch for the defrost cycle. For a while it was fixable, but eventually needed replacement.

It had a secondary related problem in that the drain tube (which, as seems usual, ran to a plastic tray on top of the compressor) had become blocked, so the melted ice was not draining away.

This leads to another caution - if you have had to do a serious manual defrost, the amount of water liberated will most likely be more than the catch tray can hold, so will probably overflow onto your flooring.

Chris

Reply to
Chris J Dixon

Bunged up drain hole to the evaporator tray? I had this on a Fridgemaster on. Unbunged it with a bit of stiff wire and no further build up I have to say though that these seem to be a bit of a black art sometimes. Clearly they work but to get the balance correct between removing the moisture and not letting it thaw out completely always seems counter intuitive. Brian

Reply to
Brian Gaff

over a few weeks. I am becoming convinced that a good defrost will sort it out but will try direct connection to the defrost heater with the contents inside and a thermometer monitoring the contents temperature.

Reply to
Bob Minchin

We had this some years back on a Whirlpool- it took their engineers ages to fix it - it was a simple timer sticking. We lost several freezer loads of food, it cost Whirlpool a fortunate.

As for defrosting manually, we 'turn around' ours in half a day or so. We have several freezers (we stock up on meat, fish etc at CostCo) and run one down so we can defrost one.

Reply to
Brian Reay

I defrost our conventional fridge freezer four times per year using a hair dryer. It takes less than 30 minutes to do this and gives me the chance to clean all of the drawers, chuck out of date stuff and clean the inside of the cabinet and the seals. People with frost free will probably not clean etc as they see no need. Sad is this. There is no way that a frost free appliance will ever enter our kitchen. Apart from insulation failure which is very rare these day there are two things that can fail with my conventional fridge freezer - thermostat = ?10 or less ---- compressor which is end of days. Now, take a look at the workings of a frost free lump of shit .....................

Reply to
Mr Pounder Esquire

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