The following components enable the engine to drive the
A/C system compressor:
| • | The A/C compressor clutch |
| | The clutch allows the compressor to disengage when air conditioning
is not required. |
Battery voltage is supplied to the following components when the ignition
switch is in the RUN position:
| • | The HVAC control module |
| • | The A/C compressor clutch relay coil |
| • | The A/C compressor clutch relay contact |
| | The A/C compressor clutch relay contact is normally open. |
The A/C compressor clutch coil must be energized in order to drive the
A/C compressor clutch. The clutch coil is energized when the clutch relay
is energized. The relay contact on CKT 59 (DK GRN) supplies voltage
to the clutch coil. Diode D104 in the harness is reverse-biased. Diode D104
prevents current flow bypassing the clutch coil to the ground. The following
conditions occur when the relay coil is de-energized:
| • | The collapsing magnetic field of the clutch coil forward-biases
the diode. |
| • | Energy dissipates from the magnetic field. |
The A/C Compressor Clutch Relay is energized when a ground path is provided
for the relay coil on CKT 459 (DK GRN/WHT). The following components
provide this ground through contact-equivalents in the module:
| • | The Powertrain Control Module (PCM) on diesel engines only |
| • | The Vehicle Control Module (VCM) on gasoline only |
The above modules may stop the compressor operations while otherwise
enabled under certain operating conditions. Refer to Engine Controls for these
conditions.
The VCM or PCM modules enable A/C compressor clutch operations when
a voltage input is received from the HVAC control module on CKT 762
(DK GRN/WHT). Two switch contacts in series between the HVAC control module
and the VCM/PCM module may isolate this voltage. The A/C compressor high pressure
cutout switch monitors the compressor high side pressure. When this pressure
exceeds a limit, the switch contacts open in order to stop the compressor.
This action reduces the pressure. This switch does not operate unless conditions
are unusual. The A/C compressor cycling switch monitors compressor low side
pressure in order to provide freeze protection. When the low side pressure
reaches a limit, the switch contacts open. When the pressure recovers, the
contacts close. This switch operates normally in order to cycle the compressor
while operating.
The HVAC control module places voltage on CKT 66 (LT GRN) under
the following conditions:
| • | The ignition switch is in the RUN position. |
| • | The mode selector switch on the module is at one of the following
detent positions: |
