Gas Furnace: TUX1/TDX1

Re: Flashing Code 3

Code 3 = Pressure switch fault

A Code 3 will result from either of the following conditions:

• Pressure switch contacts "Closed" when the inducer motor is commanded OFF.
• Pressure switch contacts "Open" when the inducer motor is commanded ON.

► If the pressure switch is in the "Closed" position when a call for heat is initiated, the control board will flash a Code 3 and NOT power the inducer motor.

CHECKOUT:

1. Check Sequence

• Activate a call for heat from the thermostat (confirm 24VAC between "W" and "C")
  • Inducer Fan Starts → Step 3. Check Pressure Switch
  • No Inducer Fan + Code 3 ⇒ Remove one wire from the pressure switch.
    • Inducer Motor Starts = Pressure Switch Stuck Closed
    • Inducer Still Doesn't Run → Step 2. Check Inducer Motor

2. Check Inducer Motor

• With "W' energized, check for 120V power at the inducer motor wiring plug:
  • Pressure Switch Open + No Power = Bad Control Board
  • Power + No Fan = Bad Inducer Motor or Capacitor

3. Check Pressure Switch

• Check Switch Contacts
• With "W" energized and the Inducer Running:
• Check for 24VAC from both sides of the pressure switch to "C".
  • Power on Both Sides = Switch Closed
  • Power on One Side Only = Switch Open
    • Inducer Running + Switch Closed + Code 3 = Bad Control Board
• Check Pressure
• Hook-up a pressure gauge to the pressure switch hoses.
  • On a 2-hose switch, connect the (-) side to the inducer and the (+) to the burner box to read "differential" pressure.
• Monitor the system pressure as the furnace operates.
  • Pressure Well Above Rating + Open Switch = Bad Pressure Switch
  • Pressure Near or Below the Switch Rating = Vent/Intake Issue ⇒ Check the negative pressure at the inducer and burner box individually.
    • Inducer Negative Pressure Low = Vent or Drain Problem
    • Burner Box Negative Pressure High = Intake Problem

4. Check Condensate Drain

• Listen for the sound of gurgling water in the inducer.
• Disconnect and check the drains from the inducer and/or collector box.

5. ADPS Switch Setting

• The ADPS switch will sometimes fail to re-open when set for the lowest setting.