Ducane Gas Furnace: 92AF

Re: Flashing Code 3

If, after the vent blower is energized, the pressure switch does not close, the control will keep the blower on and wait for the switch to close. The diagnostic code for this problem is 3 short flashes followed by a pause.

► The diagnostic code will go away once the pressure switch closes.

CHECKOUT:

1. Check Heat Sequence

• Start the furnace with a call for heat.
  • Inducer motor should start within 15 seconds.
    • Inducer motor starts & runs normally → Step 3. Check Pressure Switch
    • Inducer motor does not attempt to start & shows Code 3:
      • Check for 115V power to inducer.
        • No Power = Bad Control Board
        • Power + No Inducer → Step 2.  Check Inducer Motor

2. Check Inducer Motor

• Start the furnace with a call for heat.
• Observe and listen to inducer motor operation.
  • Inducer motor hums but does not start:
    • Bad Inducer Motor or Capacitor
    • Item in Inducer or Melted Blower Wheel (Remove inducer & check)
      • Remove Inducer, check for obstruction, re-install inducer → Step 4. Check Condensate Drain

3. Check Pressure Switch

• Check for 24VAC between each side of the pressure switch and "C"
  • Power on Both Sides + Code 3 = Bad Ignition Control Board
  • Power on One Side Only = Pressure Switch Open
• Use a pressure meter to check the pressure at the switch.
  • On a two-hose switch, be sure to check both sides at the same time (differential pressure)
• Compare actual pressure to pressure rating on the switch.
  • Pressure Near or Below Rating = Blocked or Restricted Vent
    • Check Each Pressure Side Individually 
      • Inducer Side Low = Blocked or Restricted Vent
      • Collector Box Side High = Clogged Drain
  • Pressure Well Above Rating + Open Switch = Bad Pressure Switch 

4. Check Condensate Drainage

• The furnace drain must be trapped.
• The trap must have an air gap immediately after the trap.