Low Idle With A/C On (Econoline 4.6L, 5.4L & 6.8L)
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2002 Mercury Sable, 2002 Mercury Mountaineer, 2002 Mercury Grand Marquis, 2002 Mercury Cougar, and 2002 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, step 10) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - GASOLINE & NGV article.