I was looking around to find out if there was a better way to do defrosting than my current method (which is very basic, if the return temperature is less than X for however long then defrost).
I came across this interesting article:
Why Are Heat Pumps So Dumb About Frost?
So it got me thinking. I have noticed that frosting is related to external dew point so a combination of humidity sensor, barometric pressure and temperature seems a good combination.
There are really cheap pressure/temperature/humidity sensors available, the BME280 being one so seems like a good idea to order some and experiment...
Acuario