Relays and Switches

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.

COMPRESSOR RELAY
The compressor relay provides battery voltage to the compressor clutch coil. The relay is controlled by the vehicle control module (VCM).

HIGH PRESSURE CUTOFF SWITCH
The system is also equipped with a high pressure cutoff switch. This switch is normally closed, and opens at 2827-3103 kPa (410-450 psi) to interrupt the voltage to the compressor clutch coil. This will stop the compressor from cycling and prevent the pressure relief valve from discharging refrigerant and oil.

PRESSURE CYCLING SWITCH
The refrigeration cycle (on and off operation of the compressor) is controlled by a switch that senses the low-side pressure as an indicator of evaporator temperature. The pressure cycling switch is the freeze protection device in the system and 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 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 could be insufficient to close the contacts of the pressure switch. In the event of a low charge, insufficient cooling accompanied by rapid compressor clutch cycling will be noticed at high outside (ambient) air temperatures.

If replacement of the pressure cycling switch is necessary, it is important to note that this may be done without removing the refrigerant charge. During replacement of the pressure switch, a new O-ring seal must be installed and the switch assembled to the specified torque of 4.5 Nm (40 lbs. in.).