Fridge controller - also see data logger
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Fridge is a Dometic CR50 compressor fridge - that has a standard Secop 12v compressor controller built in.
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 as I assume this is about optimal for temperature measurement.

After much research I went with a W1209 controller (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 - within 0.1 of a degree.
The temperature can easily be adjusted
The controller is not effected by vibration

I have wired in the relay of the new controller to switch the existing fridge controller, this is to keep the fridge as standard as possible while still having the accurate control of the micro processor system.
This modification gives great confidence as I now know the fridge is cold enough at all times.

Forced ventilation
The area behind the fridge was getting hot, the fridge needs to move a lot of heat from the compressor and heat exchanger, when this area gets hot the fridge is less efficient.
When the van was built there was a small vent 

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 when the engine is running.
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 - now installed and working, see link at top of page.
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

Fridge temperature shift circuit


Manual 1
Manual 2

Setup
To set minimum temp the fridge will get to - short press on set and display will flash use the up / down buttons to set - usually set to 7 degrees

To set the hysteresis
Press and hold the set button until P0 is shown
step to P1  - this is the difference between the set temp and the temp the fridge will cut back in again - usually set to 1 to 1.5 degrees

SO if the set temp is set to 7 degrees and the P1 is set to 1 degree the fridge will run until down to 7 degrees then stop - when the temp drifts up to 8 degrees the fridge will run again

Nothing else should need setting
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