Any refrigeration experts out there?

So, I've got my kegerator (a used True TDD-1), which was working great for a couple of weeks after I picked it up. However, it now has a problem where it periodically will stop cooling, and actually warm the air in the kegerator. Up to maybe 15 degrees above ambient temperature. If I shut off the cooling and then turn it back on, it tends to reset it and start cooling normally again. Anyone have any ideas on what might cause this?

Stuck thermostat?? Just a guess.