The compressor for the air conditioning system is belt-driven
by the engine through the A/C compressor clutch. The clutch allows the compressor
to perform the following functions:
| • | To engage for A/C and defroster operation |
| • | To disengage when the air conditioning is not requested |
| • | To disengage when the engine load must be reduced |
Battery voltage is supplied to the Powertrain Control Module (PCM) when
the A/C control is activated or when the heater- A/C control mode selector
is placed in any of the following modes:
The voltage signal tells the PCM that A/C compressor operation is requested.
Under normal operating conditions, the following actions occur:
- The PCM supplies a ground to the relay coil of the A/C CLU relay.
- The relay energizes.
- Voltage is supplied to the A/C compressor clutch coil through
the relay center fuse.
- The A/C compressor clutch coil engages.
- The compressor runs.
If the PCM determines that the engine load should be reduced, such as
during full throttle conditions, the PCM de-energizes the A/C CLU relay in
order to disengage the compressor clutch coil. The de-energization occurs
even though the voltage signal from the heater-A/C control is still
present at the PCM.
The A/C CLU diode provides a path for the high current that results
from voltage spikes generated from the collapsing magnetic field of
the A/C compressor clutch coil. Voltage spikes occur every time the
coil de-energizes.
