Refrigerant Pressure Sensor / Switch: Description and Operation

Pressure Cycling Switch:

PRESSURE CYCLING SWITCH

This switch controls evaporator temperature. It cycles the compressor clutch off when the evaporator temperature gets too low. It cycles the compressor back on after the evaporator temperature has increased (see accompanying figure). This cycling causes slight increases and decreases in engine speed to maintain desired cooling and prevent the evaporator from freezing.

When the ignition switch is turned "OFF" with the system operating, the refrigerant will flow from the high-pressure side of the expansion tube (orifice) to the low-pressure side until the pressure is equalized. This may be detected as a faint sound of liquid flowing for 30 to 60 seconds and is a normal condition

The cycling pressure switch provides inherent compressor protection so a separate low pressure switch is not necessary. The switch also acts as an ambient switch since at ambient freezing temperatures it will not allow the compressor to engage. Adjusting the set screw one-half turn left or right will rise or lower the settings 20.7 kPa (3 psi).