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 compressor
control.
- The relay energizes.
- Voltage is supplied to the A/C compressor clutch through the relay
center fuse.
- The A/C compressor clutch 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 relay of the A/C
compressor control in order to disengage the compressor clutch. The
de-energization occurs even though the voltage signal from the heater
and A/C control is still present at the PCM.
The diode of the A/C compressor clutch connects across the terminals
of the A/C compressor clutch. The 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.
