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Home >> Mercury >> 2009 >> Sable Base, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 185 (HVAC Control System - General Information) >> Diagnosis And Testing >> Climate Control System >> Pinpoint Tests >> Pinpoint Test J: The A/C Is Always On >> Normal Operation
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Normal Operation

WARNING: This page is about a different car, the 2005 Mercury Montego, 2005 Ford Freestyle, and 2005 Ford Five Hundred. However, it is still accessible from the selected car via links, so may be relevant.

Under normal operation, when A/C is requested, a message is sent over the MSCAN bus to the instrument cluster, then from the instrument cluster through the HSCAN bus to the PCM (EATC systems) or a voltage is sent to the instrument cluster through circuit 1424 (TN/BK) then a message from the instrument cluster through the HSCAN bus to the PCM (EMTC systems).

Ignition voltage for the A/C clutch relay switch is provided through circuit 3028 (DB/YE). When the PCM energizes the relay, ignition voltage is supplied to the A/C clutch through circuit 1810 (LG/OG). Ground is supplied for the A/C clutch through circuit 1205 (BK).

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