York Gas Furnace: PT9

Re: Flashing Code 3

Code 3 = The 1LP pressure switch contact did not close during 1st stg heat operation, or the 2LP pressure switch contact did not close during 2nd stg heat operation

► The 1LP switch is typically rated for 0.75" w.c. and the 2LP switch is typically rated for 1.25." w.c.

► Both switches are 2-port (negative port from the inducer, positive to the enclosed burner box).

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 → Step 2. Check Pressure Switch
  • Inducer motor hums but does not start:
    • 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

• 1st Stage Heat
• Run the furnace on 1st stage only (un-hook W2 at the furnace if necessary).
• 1LP Switch Contacts
• Check for 24VAC between "C" on the terminal block and the  Blue  wire on 1LP.
• Check for 24VAC between "C" on the terminal block and the  White  wire on 1LP.
  • Power On Both Sides = Switch Closed ⇒ Check 2nd Stage Heat
  • Power on One Side Only = Switch Open ⇒ Check 1LP Pressure (below)
• Check 1LP Pressure
  • Use a pressure meter to check the pressure at the 1LP switch.
    • Must check positive & negative pressure together.
  • Compare actual pressure to pressure rating on the switch.
    • Pressure Near or Below the Switch Rating (0.75" w.c.) = Vent/Intake Issue ⇒ Check the negative pressure at the inducer and burner box individually.
      • Inducer Negative Pressure Low = Vent or Drain Problem or Inducer Problem ⇒ Remove inducer & check for obstructions or damaged wheel.
      • Burner Box Negative Pressure High = Intake Problem ⇒ Remove the burner box cover to see if pressure improves.
    • Pressure Well Above Rating + Open Switch = Bad Switch or Water in Switch
• 2nd Stage Heat
• Run the furnace at full heating (place a jumper between W1 & W2 if necessary).
• 2LP Switch Contacts
• Check for 24VAC between "C" on the terminal block and the  Org  wire on 2LP.
• Check for 24VAC between "C" on the terminal block and the  Blk  wire on 2LP.
  • Power On Both Sides = Switch Closed
  • Power on One Side Only = Switch Open ⇒ Check 2LP Pressure (below)
• Check 2LP Pressure
  • Use a pressure meter to check the pressure at the 2LP switch.
    • Must check positive & negative pressure together.
  • Compare actual pressure to pressure rating on the switch.
    • Pressure Near or Below the Switch Rating (1.25" w.c.) = Vent/Intake Issue ⇒ Check the negative pressure at the inducer and burner box individually.
      • Inducer Negative Pressure Low = Vent or Drain Problem or Inducer Problem ⇒ Remove inducer & check for obstructions or damaged wheel.
      • Burner Box Negative Pressure High = Intake Problem ⇒ Remove the burner box cover to see if pressure improves.
    • Pressure Well Above Rating + Open Switch = Bad Switch or Water in Switch

3. Check Condensate Drainage

• Remove the drain hoses from both Robber Drain Couplings on the inducer outlet.
  • Water running out of coupling = Clogged Drainage
  • On horizontal runs, make sure the drain outlets are pointed slightly down-hill.
  • ► Look inside the drain fittings to make sure there is no obstruction.
• Remove the drain hoses from the inducer motor and collector box.
  • Water running out of collector box or inducer = Clogged Drainage
  • Make sure all drain hoses are clear and have a downward slope.
  • ► Look inside the drain fittings to make sure there is no obstruction.
• Remove the hoses from the condensate trap.
  • ​​​​​​​Water running out of hoses = Clogged Drainage
• Remove the condensate trap and make sure it is not clogged.
• ► In extreme cold conditions, be cautious of frozen drains.