Fridge Freezer Thermostat

I've got a Hotpoint fridge freezer - upright, 2-door affair. Top half is the fridge, bottom half is the freezer. The unit has a single compressor and there's only one mechano-electrical thermostat - in the fridge compartment with the end of its sensor tube connected to the back of the fridge 'cold plate' heat exchanger.
Last week the thermostat packed up. I called out a local appliance repair firm and they changed the thermostat. However, even on its warmest setting it ran too cold - the freezer was at least -24C and the fridge compartment was too cold: the water in the drain gutter under the 'cold plate' on the fridge rear wall was frozen.
Today they came to replace the new thermostat, but it seems that the it was not faulty because the same thing is happening with this second replacement thermostat.
I have dismantled the original, failed thermostat and notice there are 2 adjustment screws and 3 contacts. I notice that the middle contact is connected to one of the outer contacts at all times unless the thermostat is turned to Off, and that the 2 outer contacts appear to make and break depending on whether the sealed bellows has triggered them. I can't figure out why there are 3 contacts, though and there's no circuit diagram. But I imagine that the 2 factory preset screws control the temperatures at which the compressor comes on and goes off. I'd be grateful for some advice on how these thermostats work and how best to go about tweaking the screws.
(Is there a heater in the fridge 'cold plate' or does it defrost naturally during the compressor off part of the cycle?)
Any clarification of the functioning would be much appreciated.
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Follwing the replacement of the cold control thermostat in my Hotpoint fridge with a "universal" one and problems getting it to run without freezing everything, I contacted a brilliant site www.fridgedoctor.com and they sent me the circuit diagram of the cold control thermostat and I can now see that it was incorrectly fitted. This site also produces an excellent book and cd that I've sent off for on fridge repairs.
I have also discovered the function of the 2 factory preset screws in the thermostat as follows:
Hotpoint RF60 - 20 year old fridge freezer. The freezer is at the bottom and there's a single cold control in the fridge governing both units. This thermostat failed. The repair firm fitted a universal replacement and caused me no end of trouble as it ran too cold even with the control knob set at its lowest.
There are 2 factory preset screws in the body of the thermostat and here are my findings on what they do.
The first screw - the External screw - has its head on the outside of the body of the thermostat. This screw shifts both the make and break temps of the contacts i.e. the temps at which the compressor comes on and goes off. Clockwise shifts both temps warmer. (Anti-clockwise the reverse.)
The second screw- the Internal screw - has its head visible through a hole in the top of the body adjacent to the external screw. This screw, like the cold control knob, only shifts the break point of the contacts i.e. the temp at which the compressor switches off. Anticlockwise makes it switch off at a warmer temp etc.
I found a screw under the plastic cover plate behind the contacts. It acts as a stop for the contacts. I did not find any effect on temp of adjusting this screw.
Hope this helps someone in the future to avoid the trouble I've had.
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Book marked against the day - thank you.
Mary

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On Wed, 19 Apr 2006 11:01:40 +0100, Mary Fisher wrote:

Dunno. Our fridge/freezer thermostat's just gone and I thought it mightbe worth a look. Unfortunately the site is (a) commercial: pay to look (b) USAnian.
However there's a yahoo group appliance-repair at http://finance.groups.yahoo.com/group/appliance-repair / (dunno why it's in the finance section)
This is more of a DIY group (ISTR it was started by an inmate of our very own group).
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I'll look at that too! In the absence of anything one keeps straws, against the day :-)

Mary
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Mary Fisher wrote:

Another superb post for the archive - future generations will thank you one day.
Do let us know what you're bookmarking tomorrow Mary, I can hardly wait!
Mathew
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wrote in message

http://www.bialith.com/Teaching/PathologyPG/BAMscEndometrium.pdf
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Mary Fisher wrote:

Get well soon.
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:-)
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