"John Woodgate" wrote in message
...
I read in sci.electronics.design that Sam Goldwasser
wrote (in )
about 'Frost free / Auto defrost?', on Tue, 10 Aug 2004:

So you heat your food when the compressor isn't running?
'Heat' is a big word. It's about a 5 W heater embedded in the cooling
coil plate.
These systems normally also have a fan from the cooler module. This is
switched off, when the cooler is being defrosted. So the main freezer
contents only 'warm', by perhaps half a degree in the entire cycle.

That forms an
oscillator with a frequency dependant on ambient temperature and the
quality of the fridge's insulation. I guess what you mean is that
it
defrosts until another thermostat says there isn't any more ice.

No, just the one thermostat. It opens at about 0 C, stopping the
compressor, and the heater then warms up the plate to about 5 C, when
the thermostat closes again and cuts off the heat. I won't go to law on
the precise temperatures.
It is worth making a comment here about the 'Hotpoint' units, that have
had some significant bad reports here. I have one. A few months from new,
it developed the sort of problem being discussed. The engineer who came
said it was a known problem with the module, and replaced it with a new
design. The original system was a fairly basic mechanical timer, and
thermostat. The new module was a solid state system, with a temperature
pickup that had to be attached to the cooler assembly. I have had this now
for over eighteen months, without any problems at all. Hopefully new units
would have this design.

Best Wishes