Fridge controller
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Fridge is a Dometic CR50 compressor fridge
The fridge works well and keeps our food cool and supplies ice for the gin, I wanted a proper fridge freezer for our travels, as we cook a lot and want to keep
our food fresh.

I was never really happy with the way the built in thermostat controlled the fridge and I never really had any real idea of the temperature inside the fridge
I decided to replace the thermostat with a thermister linked to a microprocessor controller
I have fitted the thermister inside the fridge where the existing thermostat takes the temperature

After much research I went with a W1209 (less then £4 on eBay)
The advantages are massive
There is a constant display of fridge temperature
The compressor cut in / cut out temperature can be set precisely
The temperature can easily be adjusted
The controller is not effected by vibration

Gives great confidence as I now know the fridge is cold enough at all times
Additional temp shift mod
I thought it could be handy to get the fridge to run one degree colder when driving as power is always available from the split charge system
The idea being that when the van is stopped it would at least 1 degree below the compressor restart temp
This feature works by putting a resistor in parallel with the existing thermister, this spoofs the
controller into think the fridge is 1 degree warmer than it really is, there is a relay that is switched from
the cab (next to the headlight beam adjust) that powers the relay (only active when the ignition is on.
Diagram below.


Future modifications may include data logging,
I have left the system so I can switch back if I ever would choose to do this ! 

Pic of the controller mounted in the cupboard next to the fridge
not working
Fridge temperature shift circuit


Manual 1
Manual 2