PM9 - Flashing Code 5

York 97% Modulating Gas Furnace: PM9

Re: Flashing Code 5

Flashing Code 5 = Rollout Switch or Aux Limit Switch (on inducer)

The rollout switches and the aux limit switch are wired in series, so either switch opening during a call for heat will cause a Code 5.

CHECKOUT:

1. Check Rollout Switch

• Reset the furnace by cycling power.
• Start a call for heat by energizing "W".
• Monitor the LED on the furnace board for a lockout indication.
  • If the furnace fires and operates → Step 2. Check Aux Limit Switch
  • If the board immediately goes into a Code 5 ⇒ Check for 24VAC to "C" on each side of the Rollout Switch.
    • Power on Both Sides → Step 2. Check Aux Limit Switch
    • Power on One Side Only = Tripped Rollout Switch ⇒ Push reset button and recheck a heat cycle.

2. Check Aux Limit Switch

• Check for 24VAC to "C" on each side of the Aux Limit Switch (mounted on the inducer housing).
  • Power on One Side Only = Open Aux Limit Switch ​​​​​​​
    • Open Switch + Cold Inducer = Bad Aux Limit Switch
    • Open Switch + Hot Inducer ⇒ Wait for limit to reset then → Step 3. Check Gas Pressure
  • ​​​​​​​Power on Both Sides ⇒ Allow furnace to operate and recheck 24VAC across switch immediately when furnace shuts off.

3. Check Gas Pressure

• Start the furnace in Test Mode and force 100% firing rate.
• Check manifold gas pressure.
• Manifold Pressure should be between 2.5 - 3.5" w.c.
  • ​​​​​​​Lower gas pressure if necessary.
    • ​​​​​​​Adjustment screw is a small Allen screw under a small cap on the outlet side of the gas valve.

4. Check Vent Temperature

• Drill a small hole in the exhaust pipe near the furnace.
• As the furnace operates, monitor the flue temperature.
  • Normal 90% Furnace exhaust temperature = 100 - 130 deg. F.