In 2009, I wanted to build an Ethernet-enabled thermostat that logged temperature and humidity. I had some ideas for controling heating/cooling based on humidity as well temperature. I also wanted it to log and graph measurements for analysis.
During that time, our refridgerator/freezer began acting up. We wound find that it did not defrost properly and ended up with a warm refridgerator. At that time, I was using a microcontroller board from a company called Netburner and had already written code to read temperature sensors and do logging/graphing to a webpage interface.
I had three temperature sensors. I connected them to long wires and placed them in the:
I had read online that freezers contain small defrost switch to stop the defrost cycle early once the freezer area gets warm enough. Water had gotten inside of mine and frozen it in the always-open-circuit position. Oddly enough, it actually appeared to function fine when removed from the freezer but would later ice-up and fail. When the switch was bypassed, I noticed the freezer temperature would rise to ~40F during the defrost cycle. After a new switch was installed, I saw a similar pattern, but the defrost cycle was shortened by it. I ended up learning how freezers worked and only spent ~$20 on the replacement sensor -- much cheaper than a service call.