Low-pressure controls are used on many medium-temperature refrigeration systems to control case temperature. In order for this type of control to work properly, both its cut-in and differential pressure settings must be set correctly.
The control's cut in setting must be set to cycle the compressor back on at a pressure that will ensure adequate defrosting of the evaporator, and at a case temperature that is not too high for the product being refrigerated. For some applications, this may be at a saturation pressure corresponding to a 38°F saturation temperature.