An insulated ice making compartment is provided in the fresh food compartment of a bottom mount refrigerator. The ice making compartment may be integrally formed with the liner of the fresh food compartment, or alternatively, may be modular for installation anywhere in the fresh food compartment. A removable bin assembly with a front cover normally seals the ice making compartment to maintain the temperature in the compartment. A cold air duct formed in the rear wall of the refrigerator supplies cold air from the freezer compartment to the ice making compartment. A return air duct directs a portion of the air from the ice making compartment back to the freezer compartment. An air vent in the ice making compartment directs another portion of air into the fresh food compartment. A control system provides for controlling refrigerator functions in a manner that promotes energy efficiency. The refrigerator has a modular water tank assembly housed in a cavity in the back wall of the cabinet.