Refrigerant Pressure Sensor / Switch: Description and Operation

PRESSURE CYCLING SWITCH

The pressure cycling switch controls the ON and OFF operation of the compressor. This switch, which is mounted on a low-side fitting, is the freeze protection device in the refrigeration system. The pressure cycling switch operates by sensing the low-side refrigerant pressure as an indicator of the evaporator temperature. During cold weather, the pressure cycling switch also provides compressor cutoff.

The operating characteristics of the low-side pressure cycling system provide additional compressor protection. If a massive discharge occurs in the low-side of the system, or the orifice tube becomes plugged, low-side pressures could be insufficient to close the contacts of the pressure switch. In the event of a low charge, insufficient cooling accompanied by rapid compressor clutch cycling is noticeable at high ambient air temperatures.

Do not remove the refrigerant charge in order to replace the pressure cycling switch. The pressure switch fitting has a service fitting. A new O-ring seal must be installed when replacing the pressure switch, and the switch must be assembled to the specified torque of 4.5 N.m (40 lb in).