Hi speedy May be it depends on the brand...when you turn off the refrigerator the cooling lines(inside the fridge ,behind plastic covers) build up moisture and it turn into water,it normally get drain into the water collecting basket,but when you turn it on after a while the water vapor on lines can turn into hard ice.In the long run if this pattern continues mechanical(thermostat and coil pack) and ventilation holes can get blocked from ice...just remove the plastic plate behind your defrezzer. If you have a failing thermostat you can see ton of hard ice covering the mechanism...