Re: counter fridge not defrosting
Is the ice build up even over the rear panel ?.
If the ice build up is just near the top then it would be a refrigerant or compressor problem and on a small fridge would be beyond economical repair and is not a DIY job.
If it is evenly over the back then make sure you have wired the new thermostat correctly and check the compressor turns off with the stat set at zero.
If it runs with the stat at zero then the stat is wired incorrectly.
Bob