York Gas Furnace: TM9T

Re: No Heat or Cool - Flashing Code 9

Code 9 = Indicates reversed line voltage polarity, reversed low voltage wiring, or Grounding problem

CHECKOUT:

1. Check Grounding & Power

• Inspect the incoming power for a connected Ground wire.
• Check voltage from "Neutral" to the grounded furnace cabinet.
  • Any voltage reading = Improper Ground or Reversed Line Voltage
    • Check voltage from "Hot" to the grounded furnace cabinet.
      • No Voltage = Reversed Line Voltage
      • Partial Voltage = Improper Ground

2. Check Neutral

• After confirming a good "Ground", check voltage from "Hot" to the grounded furnace cabinet.
• Compare voltage from "Hot" to "Neutral".
  • Low voltage between "Hot" and "Neutral" = Loose "Neutral" Wire
    • ​​​​​​​Look for a loose or burnt Neutral connection between the furnace and power source.

3. Check Low Voltage Polarity

• Turn off power to the furnace.
• Try reversing the two secondary (low voltage) wires at the furnace transformer.
• Re-apply power to the furnace.
  • ​​​​​​​Still Code 9 ⇒ Suspect a Bad Control Board​​​​​​​