Under normal operating conditions your wine / beverage cooler or kegerator should not show signs of frost buildup. However, if your unit is located in an area that is subject to high levels of humidity there may be the possibility of frost occurring, typically on the back interior wall of the unit. This occurs as warmer humid air enters the inside of the unit faster than the humidity can be removed by the cooling system. If possible, try limiting the number of times the door is open and closed.
Please refer to your instruction manual or visit the below help article for additional information on how to manually defrost your wine / beverage cooler or kegerator.