TUD/TDD - Flashing Code 3

Trane Gas Furnace: TUD1/TDD1

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 they should be open.
• Pressure switch contacts "open" when they should be closed.

► 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 between the White & Black 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 Only One Side = Switch Open
    • Switch Closed + Code 3 = Bad Control Board
• Check Pressure
• Hook-up a pressure gauge to the pressure switch hoses.
• Monitor the system pressure as the furnace operates.
  • Pressure Well Above Rating (typically .60" w.c.) + Open Switch = Bad Pressure Switch
  • Pressure Near or Below the Switch Rating (typically .60" w.c.) = Vent Problem, Damaged Blower Wheel or Item in Inducer ⇒ Remove the inducer and check the inducer wheel.
    • Inducer Wheel Ok ⇒ Check the Vent

4. ADPS Pressure Switch Set Too Low

• An ADPS pressure switch with an adjustable dial sometimes fails to re-open if set too low.