For 1990-2009 cars

Scan Tool Output Control | Additional Menu Selection(s) | Description
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A/C Compressor | Special Functions, Engine Output Controls | The scan tool displays on or off selections. This command allows you to turn the A/C MG relay ON or OFF. This on or off status information represents only what the scan tool has commanded, not what action was actually taken. The blower switch and the A/C switch must be in the ON position for the scan tool command to work. Engaging the A/C relay will also engage the cooling fans at low speed.