Home >> Buick >> 2015 >> Regal GS, AWD >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> HVAC System - Automatic >> Diagnostic Information and Procedures >> DTC P0645, P0646, or P0647: Air Conditioning (A/C) Compressor Clutch Relay >> Conditions for Running the DTC