A control is provided for controlling the operation of a climate control system, which includes a processor that is capable of receiving power from a low voltage power supply adapted to be connected to an external alternating current power source, or a second external low voltage power supply. The processor is capable of storing diagnostic information pertaining to the operating status of at least one component of the climate control system. The processor is configured to retrieve stored diagnostic information from memory pertaining to the climate control system and send the diagnostic information to the display means when the processor receives power from the external low voltage power supply and detects the absence of a connection to an external alternating current power source.