The use of a low-pressure control to maintain box temperature on commercial medium-temperature applications has been a common practice for many years. It allows remote condensing units to be controlled without any additional control wiring between the refrigerated box and its compressor.
It works on the principle that there is a direct relationship between the pressure of the saturated refrigerant in the evaporator and its temperature.
A typical low-pressure control has two setpoints: its cut-in and its differential. In order for the control to work properly, both the cut-in and differential setpoints need to be set properly.Most manufacturers have stated values for the proper setpoints for their systems. However, these values usually only work well on self-contained or close-coupled systems. If the condensing unit is remotely located, the stated values may cause problems with the cooler.