A/C Condenser Fan
When the Ignition Switch is in the RUN position voltage is applied to
the coil of the Blower Relay 3 through Circuit Breaker #6. Since the coil
of Blower Relay is grounded at all times through G105, the Relay will energized,
close the relay contacts. Voltage is now applied at all times from Circuit
Breaker #24 through the now closed contacts of Blower Relay to the coil of
A/C Condenser Fan Relay. The coil is then grounded through the A/C Refrigerant
Pressure Cutoff Switch through the Control Assembly, which is case grounded.
The A/C Pressure Cutoff Switch will close when the A/C system pressure is
within specifications. When this switch closes, a ground path is provided
for the A/C Condenser Fan Relay, and the relay contacts will close. Voltage
is now applied from the Circuit Breaker #20 through the closed contacts of
A/C Condenser Fan Relay to the A/C Condenser Fan Motor. Since the A/C Condenser
Fan Motor is permanently grounded at G107, the fan will run.
A/C Compressor Clutch
The A/C Compressor is belt driven and the compressor's pulley rotates
whenever the engine is operating. The compressor only operates when the compressor
clutch has been 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 CKT 207 (GRN/RED). |
| • | When the Ignition Switch is in the RUN position, Circuit Breaker
#6 provides voltage to the Compressor Relay coil from the Blower Relay contacts,
through CKT 210 (LT GRN). |
The Compressor Relay contacts are normally open. When the Compressor
Relay is energized, the contacts close. The contacts apply voltage through
the CKT 203/208 (LT BLU) 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 CKT 213 (GRN/RED) to the Evaporator Temperature
Sensor. The HVAC Controller provides this ground path through the Evaporator
Temperature Sensor.
The Evaporator Temperature Sensor 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 Refrigerant Pressure Switch cycles the compressor off when the
following conditions exist:
| • | The compressor is otherwise enabled. |
| • | The refrigerant in the system rises above or falls below a set
pressure. |
A/C Refrigerant Pressure Switch
The A/C Pressure Cutoff Switch provides two functions
| • | The high pressure cutout section of this switch is normally closed
during operation of the A/C compressor. If pressure in the A/C refrigerant
lines goes too high, this switch will open, interrupting power to the A/C
Compressor. |
| • | The low pressure cutout section of this switch cycles the Condenser
Fan Relay on and off in response to refrigerant pressure. The switch opens
just above the freezing point, providing system freeze protection. The low
pressure switch closes as the system pressure rises, allowing the Condenser
Fan to run, maintaining system cooling. |
Evaporator Temperature Sensor
The Evaporator Temperature Sensor 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. |
