York 90% Gas Furnace: YM9M

Re: Flashing Code 3

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

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

This gas furnace has two pressure switches:

• A higher pressure switch (PS1) that monitors the negative pressure from the inducer (typically around -.67" w.c.).
• A low pressure switch (PS2) that monitors the collector box pressure for a clogged drain (typically -0.20" w.c.).

► ONLY the PS1 switch will generate a Code 3. (PS2 is wired in series with the Roll-Out Switches and will generate a Code 5).

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 + Code 3 = Bad Transducer or Bad Control Board ⇒ Unplug wiring to the transducer and re-try.

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 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 through the vent (clogged vent drain).
• Listen for sounds of water in the vent piping.
  • If water is gurgling in the vent, look for low spots that will hold water.
    • The vent piping must have a constant slope back toward the furnace.

3. Check Pressure Switches

• Make sure there are no sags in the pressure switch hoses that could hold water.
• Connect a "Tee" in the Pressure Switch hose from the Inducer Motor.
• Connect a pressure meter to monitor the operating pressure.
• Start the furnace with a call for heat.
• Step 1 - When the inducer motor starts, it should ramp up to close the switch contacts.
  • Switch contacts do not close at rated pressure = Bad Pressure Switch
• Step 2 - After the switch closes, the inducer motor should slow to open the switch contacts.
  • Switch contacts do not re-open = Bad Pressure Switch
• Step 3 - After the switch opens, the inducer should ramp up to once again close the switch contacts.
• Step 4 - After the switch contacts close for the 2nd time, the inducer should ramp to -1.0" w.c. and start an ignition sequence.
  • Inducer doesn't ramp to -1.0" w.c = Bad Transducer
• Step 5 - After firing and proving flame, the inducer should ramp back down to "Minimum Fire".

4. Check Condensate Drainage

• Check the rain gutter on the inducer outlet.
  • Remove the drain hose and look into the coupling for any blockage.
    • Water runs out of the coupling = Clogged Drain Hose
  • 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.