Refrigerant Pressure Sensor / Switch: Description and Operation

A/C Refrigerant Pressure Switch


The A/C refrigerant pressure switch is located in the liquid line, between the condenser and the orifice tube.

The A/C refrigerant pressure switch consists of two separate switches, the first is the A/C refrigerant pressure switch, the second is the A/C high pressure switch. The A/C refrigerant pressure switch acts to cycle the compressor on and off under conditions of abnormally low or abnormally high refrigerant pressure.

If the pressure drops below 196 kPa (28 psi) or rises above 3140 kPa (455 psi), the A/C refrigerant pressure switch opens and signals the A/C compressor control module to shut down the compressor. The A/C high pressure switch acts to cycle the cooling fans (the main radiator fan motor and the auxiliary radiator fan motor) from low to high speed operation. The change in refrigerant pressure affects the temperature of the refrigerant because the refrigerant pressure and temperature are proportional (temperature increases when pressure increases).

With the A/C on and refrigerant pressure below 1226 kPa (178 psi), indicating low refrigerant temperature, the A/C high pressure switch is closed, thus allowing both cooling fans to operate at low speed. If the refrigerant pressure exceeds 1520 kPa (220 psi), indicating high refrigerant temperature,

The A/C high pressure switch opens, thus allowing both cooling fans to operate at high speed. When the refrigerant pressure and temperature return to normal, the fan speed is reduced to low. The change in fan speed improves the condenser's ability to lower refrigerant temperatures and pressures.

Reasons for abnormally low refrigerant pressure are either an insufficient refrigerant supply or very low refrigerant temperatures. Reasons for abnormally high refrigerant pressure include extremely high refrigerant temperatures or an overcharging of the system during service.