York Gas Furnace: P1XU

Re: Flashing Code 3

Code 3 = One or More Pressure Switch(es) Open with the Inducer Energized.

• The P1XU gas furnace has a 2-stage gas valve and 2-speed inducer fan motor.
• There are two, Dual-Port Pressure Switches which monitor both low and high speed operation of the inducer motor.
  • The low pressure port (-) of both switches goes to the inducer motor and the high pressure (+) goes to the burner compartment (differential pressure).

► This code will go away once the switch(es) close.

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 & Runs Normal → Step 2. Check Pressure Switch
  • 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 3. Check Condensate Drainage
• Listen for sounds of water in vent piping.
  • If water is gurgling in vent, look for low spots in the vent piping that will hold water.
    • Vent Pipe must have a constant slope back toward the furnace (no traps, sags or droops).

2. Check Pressure Switch

• The inducer motor starts in Hi Speed (must close 1LP + 2LP), then drops to Low Speed (must close only 1LP).
  • Hi Speed + Code 3 ⇒ Check Both Switches
  • Lo Speed + Code 3 ⇒ Check 1LP Switch
• Check for 24VAC between each side of the switch and C on the control board.
  • Power on Both Sides = Switch Closed
  • Power on One Side Only = Switch Open ⇒ Check Differential Pressure
• Use a pressure meter to check the pressure at the switch.
  • Watch for water in the pressure switch hoses.
  • On a two-hose switch, be sure to check "differential pressure" by checking both sides at the same time.
• Compare actual pressure to the pressure rating on the switch.
  • Pressure Well Above Rating + Switch Open = Bad Switch or Water in Switch
  • Pressure Near or Below Rating = Clogged Drain or Restricted Vent / Intake ⇒ Continue
• Remove the burner box cover & re-check the pressures.
  • Little or No Improvement = Clogged Drain or Restricted Vent
  • Drastic Improvement = Restricted Intake 
    • Note: It is OK to operate with the burner cover removed as long as there is sufficient combustion air.

3. Check Condensate Drainage

• Remove each drain hose from the drain trap and check the hose.
  • Water pours out of a hose = Clogged Drain Trap ⇒ Remove and flush the drain trap.
• Make sure all drain hoses are clear and have a downward slope.