K 3500 Truck 4WD V8-5.7L VIN R (1998)
Refrigerant Pressure Sensor / Switch: Description and Operation
Pressure Cycling Switch
The refrigeration cycle (on and off operation of the compressor) is controlled by a switch that senses the low-side pressure as an indicator of evaporator
temperature. The pressure cycling switch is the freeze protection device in the system and senses refrigerant pressure on the suction side of the system.
This switch is mounted on a standard service low-side fitting. This switch also provides compressor cutoff during cold weather.
Additional compressor protection results from the operating characteristics of the low-side pressure cycling system. 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 will be noticed at high outside (ambient) air temperatures.
If replacement of the pressure cycling switch is necessary, it is important to note that this may be done without removing the refrigerant charge. A service
fitting is located in the pressure switch fitting. During replacement of the pressure switch, a new O-ring seal must be installed and the switch assembled
to 4.5 N.m (40 lb in).
