Back in November 2002 I had the then 22 year old fridge thermostat fail so I made an electronic one. I put a thermistor in a piece of steel 3 inches diameter and 2 inches high. As has been mentioned, that more accurately represented the temperature of objects in the fridge. Ran it to a comparator with *zero* hysteresis and then to a micro that looked for a full five minutes of uninterrupted over temp or under temp and switched the motor relay accordingly. Also put a pair of 90mm fans at the bottom of condenser, facing upward, at the back of the fridge. Also a single fan inside the fridge that blew directly on the evaporator. And put an hour meter on the motor. The compressor duty cycle dropped from 60% with the original thermostat down to 31% with the new thermostat and fans. The compressor would switch on roughly once every hour. Ran it till October this year then put it out in the rubbish when other parts of the 39 year old fridge were leaking water. Interestingly, the inside fan, a Sunon ball bearing unit ran 24/7 in 4 deg C ambient for just under 150,000 hours without any trouble at all and still sounded like it had years of life left in it.