Engine Position Sensor (8.3, 9 Liter) or Crankshaft Sensor (15 Liter) is failed
Mid range clutch solenoid coil or its wiring shorted to power
Temperature select pot open/shorted to power
Engine Position Sensor signal is failed (no signal at engine controller pin A9)
Mid range clutch solenoid coil or its wiring shorted to power
If Inadequate air flow is problematic, so clogged air filters, evaporator core air flow restricted, faulty blower fan motors, defective blower switch or faulty wiring or loose connections.