Six weeks after purchasing a new kegerator for home brewing, I was disappointed to find that it was short-cycling.  Sometimes it would turn on briefly for one or two seconds, then immediately shut off.  It would repeat this several times per hour.  Otherwise it was working fine, and there was no problem holding a constant temperature.  But these intermittent short bursts aren't good for the compressor ...or my ears.

After failing to find a solution with the manufacturer and knowing it was too late to return the unit, I decided to fix it myself.  All the hardware was in good condition.  An inspection of the circuit boards didn't show any obvious problems.  I had considered replacing the controller MCU with a new one, programmed with my own code.  But this was a no-name device without any markings.  The footprint was not compatible any common microcontrollers, making a substitution less straightforward.

The solution was to design a small PCB that fits inline between the front panel and the compressor relay.  Using a cheap ATTINY microcontroller to intercept the compressor control signal, I was able to filter out these glitches and enforce minimum on and off times.  I made a few extra boards in case someone else runs into the same problem.  It has been working fine for several years now and I have no complaints.

The project files are on github.