Low Idle With A/C On (Econoline 4.6L, 5.4L & 6.8L)
WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2003 Mercury Sable, 2003 Mercury Mountaineer, 2003 Mercury Marauder, 2003 Mercury Grand Marquis, and 2003 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
Check ACCS PID. Connect scan tool to Data Link Connector (DLC). Start engine and allow to idle. Using scan tool, access ACCS PID from PID/DATA MONITOR & RECORD menu. With A/C clutch engaged, ACCS PID value should indicate ON. On models where PCM cannot control A/C clutch on and off, PCM uses ACCS circuit to determine additional load on engine. If ACCS PID does not indicates ON, go to TEST KM: A/C CLUTCH RELAY & A/C CIRCUITS , step 10) under SYSTEM TESTS in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article.