Fixing a mini fridge

From Roberto De Almeida at

Adventures on repairing a mini fridge using YouTube videos and an Arduino

Close up of a kegerator

Lately I have developed a strange attraction to fridges, which I attribute mainly to 2 things:

  1. They are used in homebrewing for fermenting and serving beer. Lagers in particular need to be fermented in a temperature range (from 45 to 55 °F, or 7 to 13 °C) that is hard to maintain: a fridge will be too cold, and room temperature is too warm. A common solution is replacing the fridge thermostat with one rated for higher temperatures. For serving beer, homebrewers will often modify fridges so they have taps, like the image above; this is called a "keezer" or "kegerator".
  2. I have very little understanding of how a fridge works.

This is the reason why I was excited to find an old mini fridge abandoned at Facebook, with the sign "please dispose of me" and a sticker that said "basura". The fridge was dirty and with mold inside, and with luck that would be the ionly reason why it was being thrown away.

I brought the fridge home this Saturday, cleaned it up thoroughly, and crossed my fingers as I plugged it on. Nothing. Well, this was my opportunity to fix a fridge! So I woke up on Sunday determined to have it working. Together with Lidia I started to watch YouTube videos that explained "how to fix a fridge".

The first step was checking the thermostat. I was hoping that the problem would be in the thermostat, since it could be easily replaced, instead of being a problem with the compressor or with the actual cooling system. The thermostat was mechanical, and after testing it with a multimeter and a glass of ice we discovered it was always closing the circuit.

Thie meant two things: the thermostat was indeed bad, but it was not the only problem, because it would mean that the fridge should be always on. We removed the thermostat and simply connected the wires, and plugged the fridge on again. As expected, nothing happened. Something else was broken.

We went back to YouTube. The next step was testing the compressor, according to another video, by measuring the resistence across different pins. We had the same exact compressor as one of the videos, and as soon as we removed the start relay we noticed it was rattling! This meant that it was bad, exactly like in one of the videos!

Excited, we biked to Fry's and Lowe's in a search for replacement parts for the thermostat and the relay, but we couldn't find either. We would have to order online, and wait a few days before testing that the fridge would actually work. Instead of waiting, we decided to cannibalize a kegerator that we had also picked up in San Francisco this Saturday. Since it used the same compressor, we removed the relay, plugged it in our fridge and turned it on.

It worked!

This meant all we had to do now was to order the relay online and put it on the kegerator. As for the thermostat, I decided to build my own one, using an Arduino, instead of relying on a mechanical thermostat. The Arduino thermostat uses a PID controller, allowing the fridge to work in much more efficient cycles by monitoring the derivative of the temperature.

Overall, it was a very empowering experience -- getting something that was trash, and make it work again. We have a working fridge that looks just like new, and all for a cost that is negligible compared to how much we learned and the fun we had.

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