TM8E - Flashing Code 3

York Gas Furnace: TM8E

Re: Flashing Code 3

If, after the induced draft blower is energized, the pressure switch does not close, the control will keep the inducer 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 Control Board

• 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 + Inducer Does Not Run → 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/Capacitor or Item in Inducer ⇒ Remove inducer & check
• Ensure that the pressure switch closes.
  • Pressure switch fails to close → Step 3.  Check Pressure Switch

3. Check Pressure Switch

• Switch Contacts
• With the wires attached to the switch, check for 24VAC between each terminal of the switch and "C" Common.
  • 24VAC On Both Sides = Switch Closed 
  • 24VAC On One Side Only = Open Switch ⇒ Use a pressure meter to check the Switch Pressure (below).
• Switch Pressure
• Remove the Pressure Switch hose from the Inducer Motor.
• Connect a pressure meter to the Hose End or the Inducer Motor pressure port.
• Compare actual pressure to the pressure rating on the switch.
  • Pressure Near or Below Rating = Clogged or Restricted Vent
  • Pressure Well Above the Rating + Open Switch = Bad Switch