pairs of blowers are shown for example disposed for operation in the chamber 30 that is an upper pair of blowers 42 44 or fans are mounted to the top 22 of the housing 16 each of the blowers 42 44 includes a motor 46 48 respectively which is attached via a shaft 50 52 to a blower wheel 54 56 of the corresponding blower while the motors 46 48 are mounted external to the housing 16 the shafts 50 52 and blower wheels 54 56 are disposed in the chamber 30 each one of the upper blowers 42 44 is provided with a corresponding louvered housing 58 60 respectively the louvered housings 58 60 are disposed in the chamber 30 mounted to an inner surface of the top 22 of the housing 16 the remaining side walls of the louvered housings 58 60 can be selectively opened or closed as shown in fig1 and 2 to control and vary a flow rate of the chilling atmosphere in the chamber 30 for example as shown in fig1 and 2 louvers 62 64 of the corresponding louvered housings 58 60 are all in an open position for maximum circulatory air flow within the chamber 30 referring still to fig1 a lower pair of blowers 66.