The A/C relay is activated if the A/C switch is ON while the blower is running and system operation is enabled the ECM. Power is then supplied to the A/C compressor electromagnetic clutch and A/C system is operated. The A/C compressor is switched out to prevent it running when full engine output is required or there is a risk of overheating.The ECM also inhibits compressor operation on starting to permit running conditions to stabilize.