York Gas Furnaces: PUDD

Re: No Heat / Won't Come On

This condition is generally reported two different ways by the customer:

1. "The furnace won't do anything." - Indicating that there is no activity from the furnace on a call for heat.
2. "The furnace makes a noise, but it never blows-out hot air." - Indicating that the inducer motor runs, but ignition never takes place.

CHECKOUT:

1. Check Power

• Check for 24VAC between "R" and "C" on the transformer terminal block.
  • No Power ⇒ Check Blower Door Switch and High Voltage Power to Furnace
  • High Voltage but no Low Voltage ⇒ Check transformer.
• Set thermostat to call for Heat
• Check 24VAC between "W" and "C" on the transformer terminal block.
  • No Power = No Heat Call, Check Thermostat
  • Power & No Inducer = Bad Inducer or Bad Heat Relay
• Inducer Running --> Check for 24VAC between "TH" or "24V" on ignition control ad "C" on the terminal block.
  • No Power → Step 2. Check Safeties
  • Power present →  Step 3. Check Ignition Control

2. Check Safeties

• 1LP Pressure Switch (3-wire)
  • Check for 24VAC between "C" on the pressure switch (Red) & "C" on the terminal block.
    • No Power = Bad Heat Relay
  • Check for 24VAC between "NO" on the pressure switch (Yel) and "C" on the terminal block.
    • No Power = Pressure Switch Not Closed
• 2LP Pressure Switch (2-wire)
  • Check for 24VAC between "C" on the pressure switch (Yel) & "C" on the terminal block.
    • No Power = 1LP Switch Not Closed
  • Check for 24VAC between "NC" on the pressure switch (Brn) and "C" on the terminal block.
    • No Power = Pressure Switch Open
• Primary Limit
  • Check for 24VAC between the (Blk) wire of the limit to "C" on the terminal block.
    • No Power = Blown Fusible Link (Mounted in the burner compartment)
  • Check for 24VAC between the (Brn) wire of the limit to "C" on the terminal block.
    • No Power = Open Limit

3. Check Ignition Control

• Look for a flashing lockout light on the control.
  • Flashing Light = Lockout ⇒ Reset power and retry.
• Glow plug should begin glowing within 30 seconds of receiving power on "TH" or "24V".
• Gas Valve should energize within 60 seconds of powering the glow plug.
  • No Glow + Gas Valve Opens →  Step 4. Check Glow Plug
  • No Glow + No Gas Valve = Bad Ignition Control

4. Check Glow Plug

• Look for any visual cracks.
• Use a meter to test resistance of glow plug.
  • No resistance = Bad Glow Plug
• Check for 120V power to the Glow Plug during an ignition sequence.
  • No Power = Bad Ignition Control
  • Power present but no glow = Bad Glow Plug