The blower motor relay provides battery voltage to the blower motor assembly during high blower motor assembly speed. The blower motor resistor provides power to the blower motor assembly in all other speed settings.

The compressor relay provides battery voltage to the compressor clutch coil. The powertrain control module (PCM) controls the relay on four cylinder engines. The vehicle control module (VCM) controls the relay on six cylinder engines.

The system is also equipped with a high-pressure cutout switch. This switch opens at 2827-3050 kPa (410-440 psi) in order to interrupt the voltage to the compressor clutch coil. Opening the switch stops the compressor from cycling. The switch prevents the pressure relief valve from discharging refrigerant and oil.

A low pressure cutout switch protects the compressor. A low-charge condition opens the switch. This switch prevents the compressor from running in cold weather.

Pressure Cycling Switch (4.3L)

A pressure cycling switch controls the refrigeration cycle (the ON and OFF operation of the compressor). The switch senses the low-side pressure as an indicator of evaporator temperature. The switch protects the system from freezing. The switch senses refrigerant pressure on the suction side of the system. This switch is mounted on a standard service fitting on the accumulator. This switch also provides compressor cutout during cold weather.

The low-side pressure cycling system also protects the compressor. Low-side pressures might not close the contacts of the pressure switch if a massive discharge occurs in the low side of the system. Low-side pressure also might not close the contacts if the orifice tube clogs. Insufficient cooling and rapid compressor clutch cycling are noticed at high outside temperatures in the event of a low charge.

You can replace the pressure cycling switch without removing the refrigerant charge. You must install a new O-ring seal when you replace the pressure switch. The switch must be assembled to the specified torque of 4.5 N·m (40 lb in).