The battery voltage is supplied at all times to the No. 1 blower relay through the HTR A/C fuse and the RED wire. When the control assembly is in the OFF position, all the blower relays de-energize. In this state, a voltage path through the relay contacts to the blower motor does not exist. The blower motor does not run.

With the low blower speed selected, the current flows through the No. 1 relay to the top of the resistor board (A) and to both resistors.

With medium #1 blower speed selected, the current flows through the No. 1 relay, to the No. 2 relay, to the center of the resistor board (A), and one resistor to the motor.

With medium #2 blower speed selected, the current flow is the same as in medium #1. In addition, a parallel current path goes through resistor (B) and the No. 3 blower relay to the blower motor. This provides a parallel path with a value less than one alone, but more voltage than for medium #1 blower speed.

With high blower speed selected, No. 1 and No. 2 blower relays are off. Relay No. 3 is on. Relay No. 3 provides a parallel battery feed circuit to the blower motor.

This system is equipped with a compressor pressure switch that is normally open. The switch activates at 2758-2758 kPa (380-400 psi). The switch releases at 1724 kPa (250 psi).

The switch drives the recirculation door to the closed position in order to reduce the system load and decrease the system high-side pressure.

The system also has a high pressure cutoff switch. This switch is normally closed. The switch opens at 2827-3103 kPa (410-450 psi) in order to interrupt the voltage to the compressor coil. This stops the compressor from cycling, and prevents the pressure relief valve from discharging refrigerant and oil.

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. Assemble the switch to 4.5 N·m (40 lb in).