A/C Compressor Clutch
The A/C Compressor is belt driven. The pulley of the compressor rotates
whenever the engine is operating. The compressor only operates when the compressor
clutch has been energized. The clutch is engaged when the Compressor Relay
passes current to the Compressor Clutch Coil.
Compressor Relay
The Compressor Relay receives two sources of voltage:
| • | Circuit Breaker #20 provides voltage at all times to Compressor
Relay terminal 30 through the GRN/RED (207) wire. |
| • | When the Ignition Switch is in the RUN position, Circuit Breaker
#6 provides power to the Compressor Relay coil from the Blower Relay contacts,
through the LT GRN (210) wire. |
The Compressor Relay contacts are normally open. When the Compressor
Relay is energized, the contacts close. The contacts apply voltage through
the LT BLU (203,208) wire to the A/C Compressor Clutch Coil. Because the
A/C Compressor Clutch Coil is grounded internally through its case, the coil
is energized when voltage is applied.
The Compressor Relay is energized when a ground path is provided for
the relay coil through the GRN/RED (213) wire. The Air Conditioning Mode Switch
provides this ground path through the Thermo Switch.
The Thermo Switch performs the following functions:
| • | Senses the temperature of the interior vehicle air |
| • | Cycles to ground when the temperature goes above the set value |
| | This action energizes the Compressor Relay coil. |
The A/C Pressure Cutoff Switch cycles the compressor off when the following
conditions exist:
| • | The compressor is otherwise enabled. |
| • | The freon in the system reaches a set pressure. |
A/C Pressure Cutoff Switch
The A/C Pressure Cutoff Switch performs the following two functions:
| • | The high pressure cutout section of the switch is normally closed
during the operation of the A/C Compressor. |
| | The switch opens if the pressure in the A/C refrigerant lines is too
high. |
| | This action interrupts the power to the A/C compressor relay. |
| • | The low pressure cutout section of this switch cycles on and off
in response to evaporator temperature. |
| | The switch opens just above the freezing point. This action prevents
the system from freezing. |
| | The temperature switch closes as the evaporator temperature rises. This
action allows the compressor to run and to maintain system cooling. |
Thermo Switch
The Thermo Switch provides additional protection from icing conditions
in the evaporator core by performing the following actions:
| • | Sensing the evaporator core temperature. |
| • | Removing ground from the compressor relay coil when the temperature
falls below a set value. |
