York Rooftop Unit: ZF120

Re: Heat Board - Code 3

If, after the induced draft blower is energized, the pressure switch circuit 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 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 230V power to inducer.
        • No Power = Bad Ignition 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 (Remove inducer & check)
• Ensure that the pressure switch closes.
  • Pressure switch fails to close → Step 3.  Check Pressure Switch

3. Check Pressure Switch

• Use a pressure gauge to check the pressure at the switch while the inducer is running.
• Compare actual pressure to pressure rating on the switch.
  • Pressure near or below rating:
    • Rusted Inducer Blower Wheel
    • Clogged Pressure Port
  • Pressure well above rating and switch doesn't close = Bad Switch