York Gas Furnace: TM9T

Re: Flashing Code 3

Code 3 = The normally open (1LP or 3LP) pressure switch contact did not close after the inducer was energized.

► This is a "Soft Lockout" which will automatically reset after 1 hour.

► There are 3 pressure switches on this furnace. 1LP (1st Stage Switch) and 3LP (Condensate Switch) are wired in series to the pressure switch input.

► The 2LP (2nd Stage Switch) wires in separately and will cause a Code 13.

CHECKOUT:

1. Check Inducer Motor Operation

• Start the furnace with a call for heat from the thermostat.
• Observe and listen to the inducer motor operation.
  • Inducer Motor Starts and Runs Normally → Step 2. Check Pressure Switch
  • Inducer motor hums but does not start normally:
    • Bad Inducer Motor or Capacitor
    • Item in Inducer or Melted Blower Wheel ⇒ Remove inducer & check
  • Sound of water "slurshing" = Water in Inducer ⇒ Remove the Inducer, pour out water, re-install inducer → Step 3. Check Condensate Drainage
• Listen for sounds of water in vent piping.
  • If water is gurgling in vent, look for low spots that will hold water.
    • Pipe must have constant slope back toward furnace.

2. Check Pressure Switches

• 1LP (1st Stage Switch)
• Check for 24VAC between "C" on the terminal block and the Blk/Org wire on 1LP.
• Check for 24VAC between "C" on the terminal block and the Wht wire on 1LP.
  • Power On Both Sides = Switch Closed ⇒ Check 3LP Switch
  • Power on One Side Only = Switch Open ⇒ Check 1LP Pressure (below)
• 3LP (Condensate Switch)
• Check for 24VAC between "C" on the terminal block and the Wht wire on 3LP.
• Check for 24VAC between "C" on the terminal block and the Red/Grn wire on 3LP.
  • Power On Both Sides = Switch Closed
  • Power on One Side Only = Switch Open ⇒ Check 3LP Pressure (below)
• Check 1LP Pressure
  • Use a pressure meter to check the pressure at the 1LP switch.
    • Watch for water in the pressure switch hoses.
  • Compare actual pressure to pressure rating on the switch.
    • Pressure Near or Below Rating = Blocked or Restricted Vent
    • Pressure Well Above Rating + Open Switch = Bad Switch or Water in Switch
      • Water in Switch is usually caused by a mis-run pressure switch hose.
• Check 3LP Pressure
• Use a pressure meter to check the pressure at the 3LP switch.
• Compare actual pressure to pressure rating on the switch.
  • Pressure Near or Below Rating = Blocked Drain
  • Pressure Well Above Rating + Open Switch = Bad Switch

3. Check Condensate Drainage

• Check the Robber Drain Coupling on the inducer outlet.
  • On horizontal runs, make sure the drain outlets are pointed slightly down-hill.
  • Remove drain hoses.
    • Water running out of coupling = Clogged Drainage
  • ► Make sure there is nothing inside the drain coupling clogging the drain outlet.
• Check drain hoses from the collector box.
  • Make sure all drain hoses are clear and have a downward slope.
  • ► Make sure the drain outlets are not clogged.
• ! Make sure there is an "Air-Gap" in the PVC drain immediately upon exiting the furnace !
  • Any trap after the collector box before an air gap will cause drainage issues.
• In extreme cold conditions, be cautious of Frozen Drains.