York Gas Furnace: TM9X/TM9E

Re: Flashing Code 9

Code 9 = Reversed Polarity or Grounding Problem

CHECKOUT:

1. Check Line Voltage/Ground

• Check the inlet power wiring to see if there is a ground wire, and make sure that it is connected to the furnace Gnd.
• Check and record the voltage reading between L1 & Neutral (probably Black & White).
• Check the voltage reading between L1 and the Gnd.
  • (L1 to Neutral) Greater Than (L1 to Gnd) = Improper Grounding
  • (L1 to Neutral) Less Than (L1 to Gnd) = Loose Neutral
• Check voltage reading between Neutral and Gnd.
  • Any Voltage Reading = Back-Feed Voltage from Another Appliance (Not on a dedicated circuit).

2. Check Control Board Wiring

• At the furnace control board, disconnect the Black wire attached to "Line".
• Check voltage reading between Black wire and Gnd.
  • Should read full line-side voltage (Approx. 115VAC)
  • ​​​​​​​A Low or No voltage reading would indicate reversed polarity (Line & Neutral).

3. Check Low Voltage Polarity

• Check voltage reading from "R" to Gnd.
  • ​​​​​​​Should read full transformer secondary voltage (Approx. 24VAC)
• Check voltage reading from "C" to Gnd.
  • ​​​​​​​Should read 0V.
  • Any voltage reading could indicate a loss of grounding.

4. Check Flame Sensor & Control Board

• Check for a shorted flame sensor by checking resistance between Pur on Pin#2 of the board and Gnd.
  • ​​​​​​​Any resistance = Shorted Flame Sensor
• Try switching the two wires on the Load (24VAC) Side of the transformer.
  • Board Still Flashes Code 9 ⇒ Replace Control Board