Rate of change temperature control for transport refrigeration systems

A method of controlling the load temperature of a transport refrigeration system to a selected set point temperature, by operating modes which include a high capacity cooling mode and a lower capacity cooling mode, comprising the steps of:

• switching between the higher capacity cooling mode and the lower capacity cooling mode at predetermined load temperatures relative to set point,
• starting a timer having a programmable time-out period when the operating mode changes to the lower capacity cooling mode,
• monitoring the load temperature relative to set point during the lower capacity cooling mode,
• programming the time-out period of the timer in response to predetermined differences between the load temperature and set point, with the length of the time-out period varying indirectly with the magnitude of the predetermined difference temperature,
• said monitoring step including the step of providing a control signal when set point is not reached within a period of time after entering the lower capacity cooling mode which is a function of time and load temperature relative to set point, and to the programmed time-out period of the timer,
• and forcing a change from the lower capacity cooling mode to the higher capacity cooling mode in response to said control signal.