Relays and Sensors

COMPRESSOR CONTROL RELAY
The compressor clutch coil is energized through the compressor control relay. This relay is activated by the PCM in A/C modes. The PCM provides cut-off of the relay under certain operating conditions such as wide open throttle.

A/C REFRIGERANT PRESSURE SENSOR
The electronic A/C refrigerant pressure sensor is mounted to the line between the condenser and the evaporator. The output to the PCM is variable.

The output of the PCM depends on the pressure inside of the line. A higher pressure will result in a higher voltage output.

The PCM constantly monitors the A/C system pressure in order to achieve the following effects:
^ Disengage the A/C clutch if the pressure is above 2700 kPa (440 psi).
^ Disengage the A/C clutch if the pressure is below 285 kPa (38 psi).
^ Boost the idle air control in order to compensate for the A/C load at idle.
^ Control the cooling fan operation. Refer to Electrical Cooling Fan Diagnosis.

Replace the pressure sensor if the pressure sensor fails. The pressure sensor is not repairable. Refer to LINK.

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

HIGH PRESSURE CUTOFF SWITCH
The system has a high pressure cutoff switch. This switch normally closes at 1035-1379 kPa (150-200 psi). The switch opens at 2827-3103 kPa (410-450 psi) in order to interrupt the voltage to the compressor clutch coil. This stops the compressor from cycling, and prevents the pressure relief valve from discharging refrigerant and oil.

PRESSURE CYCLING SWITCH
A switch that senses the low-side pressure as an indicator of evaporator temperature controls the refrigeration cycle, the ON and OFF operation of the compressor. The pressure cycling switch is the freeze protection device in the system. The switch senses refrigerant pressure on the suction side of the system. The switch mounts 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 may be insufficient in closing the contacts of the pressure switch. In the event of a low charge, insufficient cooling accompanied by rapid compressor clutch cycling is noticeable at high outside or ambient air temperatures. DO NOT remove the refrigerant charge in order to replace the pressure cycling switch. The pressure switch fitting has a service fitting. During the replacement of the pressure switch, install a new O-ring seal and assemble the switch to the specified torque of 4.5 N.m (40 lb in).