A method for operating a transport refrigeration unit during loading of product into a compartmentalized cargo box, the cargo box having at least a first compartment having a door and a second compartment having a door, the refrigeration unit having a refrigerant flow circuit including a refrigerant compressor having a suction inlet, a main evaporator operatively associated with the first compartment and a remote evaporator operative associated with the second compartment, connected in refrigerant flow communication in a refrigeration circuit, said method characterised by comprising the steps of: determining a degree of superheat in the refrigerant at the suction inlet to the compressor; comparing said degree of suction superheat to a lower limit for the degree of superheat at the suction inlet to the compressor; continuing operation of said refrigerant unit in a refrigeration mode if said degree of suction superheat is greater than said lower limit for the degree of superheat; and terminating operation of said refrigerant unit in the refrigeration mode if said degree of suction superheat is not greater than said lower limit for the degree of superheat and initiating a defrost of at least one of the main and remote evaporators (40, 50), wherein the step of initiating a defrost of at least one of said evaporators (40, 50) comprises at least one of: determining whether the door to the second compartment is open and initiating a defrost of said remote evaporator if the door to the second compartment is determined to be open; and determining whether the door to the first compartment is open and initiating a defrost of said main evaporator if the door to the first compartment is determined to be open. determining a degree of superheat in the refrigerant at the suction inlet to the compressor; comparing said degree of suction superheat to a lower limit for the degree of superheat at the suction inlet to the compressor; continuing operation of said refrigerant unit in a refrigeration mode if said degree of suction superheat is greater than said lower limit for the degree of superheat; and terminating operation of said refrigerant unit in the refrigeration mode if said degree of suction superheat is not greater than said lower limit for the degree of superheat and initiating a defrost of at least one of the main and remote evaporators (40, 50), wherein the step of initiating a defrost of at least one of said evaporators (40, 50) comprises at least one of: determining whether the door to the second compartment is open and initiating a defrost of said remote evaporator if the door to the second compartment is determined to be open; and determining whether the door to the first compartment is open and initiating a defrost of said main evaporator if the door to the first compartment is determined to be open. determining whether the door to the second compartment is open and initiating a defrost of said remote evaporator if the door to the second compartment is determined to be open; and determining whether the door to the first compartment is open and initiating a defrost of said main evaporator if the door to the first compartment is determined to be open.