On 29/09/2017 19:10, Mr Pounder Esquire wrote:
Bob Minchin wrote:
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?

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.

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.