System Configuration Diagram For A/C relay control, the driving condition is detected by means of input signals from
the various sensors, and the A/C relay is controlled in accordance with the driving condition. The A/C-ECU applies system voltage to the engine-ECU when the air conditioner is running. When an A/C ON signal is input to the engine-ECU, the engine-ECU turns on the power transistor.
This causes current to flow to the power coil of the A/C relay. The relay switch then turns
on to operate the A/C compressor magnet clutch.
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