Carrier 80% Gas Furnaces: 58ZAV

Re: Flashing Code 31 / Fault Code 31

Light Pattern = 3 Short Flashes + 1 Long Flash (- - - , —)

Code 31 = Pressure Switch Failed to Close

On Carrier 80% Furnaces, the Pressure switch is wired in series with several other possible vent safeties, including a Blocked Vent Switch, Draft Safety Switch, Auxiliary Limit and Low Gas Pressure Switch.

Therefore, a Fault Code 31 is caused by one of the following:

• Pressure Switch failed to close or re-opened after closing.
• Draft Safety Switch Open
• Blocked Vent Switch Open
• Auxiliary Limit Switch Open
• Low Gas Pressure Switch Open

CHECKOUT:

1. Check Furnace Operation

• Start furnace with a call for heat.
  • If there is 24V on "W" at power-up, the furnace will run the blower for 90 seconds and flash a Code 12.
• Inducer motor should start and run.
  • No Inducer + Code 31 → Step 2. Check Inducer Motor
  • Inducer Runs + Code 31 → Step 3. Check Safety Circuit

2. Check Inducer Motor

• With a call for heat, check for 115VAC between the Black and White wires of the 3-pin plug for the inducer motor.
  • No Power = Bad Control Board
  • Power + No Inducer = Bad Inducer / Capacitor or Blocked Inducer Wheel 

3. Check Safety Circuit

• Check for 24VAC between "24V Com" and the Orange wire on Pin #3 of the 9-pin plug.
  • No Power = Bad Control Board
• Check for 24VAC between "24V Com" and the Yellow wire on Pin #4 of the 9-pin plug.
  • Power on Pin #3 + Power on Pin #4 + Code 13 = Bad Control Board
  • Power on Pin #3 + No power on Pin #4 = Open Circuit ⇒ Check Each Switch
    • Draft Safety Switch
    • Check for 24VAC between "24V Com" and both sides of the Draft Safety Switch.
      • Power on Both Sides = Switch OK
      • Power on One Side Only = Open Switch
    • Blocked Vent Switch
    • Check for 24VAC between "24V Com" and both sides of the Blocked Vent Safety Switch (if used).
      • Power on Both Sides = Switch OK
      • Power on One Side Only = Open Switch ⇒ Check Venting System!
    • Auxiliary Limit
    • Check for 24VAC between "24V Com" and both sides of the Auxiliary Limit Switch (horizontal or counterflow models - mounted in blower compartment).
      • Power on Both Sides = Switch OK
      • Power on One Side Only = Open Switch  ⇒ Check Blower Motor
    • Pressure Switch
    • Check for 24VAC between "24V Com" and both sides of the Pressure Switch (if used).
      • Power on Both Sides = Switch OK
      • Power on One Side Only = Open Switch ⇒ Check Pressure Switch
    • Low Gas Pressure Switch
    • Check for 24VAC between "24V Com" and both sides of the Low Gas Pressure Switch (if used).
      • Power on Both Sides = Switch OK
      • Power on One Side Only = Open Switch ⇒ Check Gas Pressure