For 1990-2009 cars

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 no requested

• | To disengage when the engine load must be reduced

Battery voltage is supplied to the powertrain control module (PCM) when the heater and A/C control mode selector knob is in the following modes:

• | MAX A/C

• | NORM A/C

• | BI-LEVEL

• | DEFOG

• | DEFROST

The voltage signal tells the PCM that A/C compressor operation is requested.

Under normal operating conditions, the following actions occur:

1. The PCM supplies a ground to the relay coil of the A/C compressor control.
2. The relay energizes.
3. Voltage is supplied to the A/C compressor clutch through the relay center fuse.
4. The A/C compressor clutch engages.
5. 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.

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 current which results from voltage spikes. Voltage spikes generate from the collapsing magnetic field of the A/C compressor clutch coil. Voltage spikes occur every time the coil de-energizes.