A/C Pressure Switches

A/C Pressure Switches:

The A/C system is protected by two pressure switches. The A/C high pressure switch opens when the A/C line pressure exceeds a predetermined value (3140 kPa (455 psi)). The A/C low pressure switch opens when the A/C line pressure falls below a predetermined value (196 kPa (28 psi)). When the A/C compressor control module sees an open in either signal, the A/C clutch relay control circuit is no longer grounded, thus shutting off the compressor. The A/C refrigerant pressure sensor is located next to the condenser fan motor in the liquid line, between the receiver/ dryer and the evaporator. The A/C refrigerant pressure sensor incorporates both the high and the low pressure switches in one unit.

The A/C compressor control module monitors the evaporator temperature sensor which is mounted on the inside of the evaporator housing. The evaporator temperature sensor converts evaporator core temperature into a resistance value. Using this resistance value, the A/C compressor control module can sense when the evaporator temperature drops below 0°C (32°F). If this occurs the A/C compressor control module removes the A/C compressor clutch relay coil ground. This prevents evaporator frost and ice build-up which reduces airflow and reduces the cooling capacity of the unit.