TG9S/GY9S - Flashing Code 3

York 90% Gas Furnace: TG9S

Re: Flashing Code 3

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

►The code description on the blower door says, "Vent or Termination Problem" which is a possible cause, but not the most likely.

This gas furnace has two pressure switches:

• A low pressure switch that monitors for a clogged drain (typically -0.20" w.c.).
• A higher pressure switch that monitors the negative pressure from the inducer (typically around -1.00" w.c.).

Either switch open after the inducer motor is commanded to start will generate a Code 3.

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.
    • Inducer Motor Starts → Step 2. Check Inducer
    • Inducer Motor Does Not Start + Code 3 ⇒ Check for 115V power to inducer.
      • Power + No Inducer → Step 2. Check Inducer
      • No Power = Bad Control Board

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)
• 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 Common.
    • 24VAC On Both Sides = Switch Closed → Check Vent Switch
    • 24VAC On One Side Only = Open Switch ⇒ Check Switch Pressure (below)
  • Switch Pressure
  • Remove the Low Pressure Switch hose from the Collector Box.
    • Water Runs Out of Collector Box = Clogged Drain → Step 4. Check Condensate Drainage
  • Inspect the pressure switch hose for a:
    • Loose hose
    • Dry-rotted, cracked hose
    • Clogged hose
  • 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
        • ** A York Service Letter changes a .40" drain switch to a .20" **
• ​​​​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 ⇒ Use a pressure meter to check the Switch Pressure (below).
  • Switch Pressure
  • Remove the High Pressure Switch hose from the Inducer Motor.
  • Inspect the pressure switch hose for a:
    • Loose hose
    • Dry-rotted, cracked hose
    • Clogged hose
  • 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 - should loop up so water drains back to the inducer (not the pressure switch).

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.