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

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The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Bob Minchin" wrote in message
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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?