system controller 26 may be arranged to determine the optimum operating dew point temperature of the anteroom 14 and to control the anteroom 14 at this optimum operating dew point temperature so that air infiltrating from the anteroom 14 into the freezer 12 will not cause fog ice and or snow in the freezer 12 additionally the system controller 26 in response to the frost sensors 48 and 50 controls conditions in the anteroom 14 so that ice will not accumulate in the anteroom 14 at the bottom of the opening of the door 10 or in the freezer 12 at the top of the opening of the door 10 accordingly the system controller 26 flags the fan and coil unit 52 in the anteroom 14 so as to cause the speed of the fan in the fan and coil unit 52 to increase to maintain better air circulation and mixing and also flags the fan and coil unit 52 to convert to heating mode when the ice from the opening of the door 10 is removed and the dry bulb temperature of the anteroom 14 is operating at set point the system controller 26 flags the fan and coil unit 52 to operate at normal conditions also the system controller 26 is responsive to the coil frost sensor 76 that is positioned to sense frost build up on the evaporator coil of the fan and coil unit 62 in order to reduce this frost build up by increasing the speed of the fan of.