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TM9X/TM9E - Flashing Code 3

Article ID: 605
Last updated: 9 Mar, 2023

York Gas Furnace: TM9X/TM9E

Re: Flashing Code 3

Code 3 = Furnace Pressure Switch failed to close on a call for heat.


  • This gas furnace has two pressure switches (PS1 & PS2) - a higher pressure switch to monitor the negative pressure at the inducer motor, and a lower pressure switch to monitor for a clogged drain at the bottom of the collector box.
  • Either switch open with the inducer motor operating will cause a Code 3.

Qty Possible Causes:
5 Bad Inducer Motor
2 Water in Pressure Hose
2 Water in the vent (improper slope)
1 Mis-Configured Hoses
Water in inducer (clogged drain)
Clogged or Restricted Vent
2 Bad Pressure Switch
Clogged / Frozen Drain
Item Stuck in Inducer Motor
Bad Ignition Control


CHECKOUT:

1. Check Control Board

  • Start the furnace with a call for heat.
  • Ensure that power is present on "W" by checking for 24VAC between "W" and "C".
    • No Power = No Call for Heat
    • Power = The Inducer motor should start within 15 seconds.

2. Check Inducer

  • Observe and listen to the inducer motor.
    • Inducer motor runs normally → Step 3. Check Pressure Switches
    • Inducer motor hums but does not start = Bad Inducer Motor/Capacitor or Item in Inducer ⇒ Remove inducer & check
    • Sound of Water "Slurshing" = Water in Inducer ⇒ Remove Inducer, pour out water, re-install inducer → Step 4.  Check Condensate Drainage
      • The only logical way for water to get into the inducer is by condensation over-running the rain gutter on the inducer outlet.
    • Listen for sounds of water in the vent piping (near the furnace and at the vent termination).
      • If water is gurgling in the vent, look for sags or low spots in the vent piping that will hold water.
        • The vent piping must have a constant slope back toward the furnace.

3. Check Pressure Switches

  • Ensure the drain and pressure switch hoses are in the proper location for the furnace orientation. (See attached file below)
  • Make sure there are no sags in the pressure switch hoses that could hold water.
  • Start the furnace with a call for heat.
  • Check Drain Switch (Low 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 ⇒ Check Vent Switch
      • 24VAC On One Side Only = Open Switch ⇒ Check Switch Pressure
    • Switch Pressure
    • Remove the Low Pressure Switch hose from the Collector Box.
    • Connect a pressure meter to the Collector Box pressure port.
    • Compare actual pressure to the pressure rating on the switch.
      • Pressure Near or Below Rating = Clogged Drain → Step 4. Check Condensate Drainage
        • Pressure Well Above the Rating + Open Switch = Bad Switch or Water in Switch
  • ​​​​Check Vent Switch (High Pressure Switch)
    • Switch Contacts
    • With the wires attached to the switch, check for 24VAC between each terminal of the switch and Common.
      • 24VAC On Both Sides = Switch Closed 
      • 24VAC On One Side Only = Open Switch ⇒  Check Switch Pressure
    • Switch Pressure
    • Remove the High Pressure Switch hose from the Inducer Motor.
    • Connect a pressure meter to 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 or Water in Switch
      • ​​​​Water in Switch is usually caused by a mis-run pressure switch hose.

4. Check Condensate Drainage

  • Check the rain gutter on the inducer outlet.
    • Remove the drain hose and look into the coupling for any blockage.
    • Make sure the drain hose is clear.
      • On horizontal runs, make sure the drain outlets are pointed slightly down-hill.
  • Check the drain hose from the collector box.
    • Make sure all drain hoses are clear and have a downward slope.
  • IMPORTANT! Make sure there is an "Air-Gap" in the PVC drain immediately upon exiting the furnace.
    • Any trap after the furnace before the air gap will cause drainage issues.
    • A tee running up to the air conditioner coil will act as an air gap.
  • In extreme cold conditions be cautious of Frozen Drains.

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Article ID: 605
Last updated: 9 Mar, 2023
Revision: 22
Access: Public
Views: 287
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