GMP - Flashing Code 3

Goodman Gas Furnace: GMP

Re: Flashing Code 3

If, after the vent blower is energized, the pressure switch does not close, the control will keep the blower on and wait for the switch to close. The diagnostic code for this problem is 3 short flashes followed by a pause.

► The diagnostic code will go away once the pressure switch closes.

CHECKOUT:

1. Check Control Board

• Start the furnace with a call for heat.
  • Inducer motor should start within 15 seconds.
    • Inducer Starts & Runs Normally → Step 3. Check Pressure Switch
    • No Inducer + Code 3 ⇒ Check for 115V power to inducer.
      • Power + No Inducer → Step 2.  Check Inducer Motor
      • No Power = Bad Control Board

2. Check Inducer Motor

• Observe and listen to inducer motor operation.
  • Inducer Motor Starts and Runs Normally → Step 3. Check Pressure Switch
  • Inducer Starts buts Is Unusually Loud:
    • Bad Inducer Blower Wheel
    • Item in Inducer ⇒  Remove inducer & check.
  • Inducer Motor Hums but Does Not Start:
    • Bad Inducer Motor or Capacitor
    • Item in Inducer ⇒ Remove inducer & check.

3. Check Pressure Switch

• Switch Contacts
• Check for 24VAC between each side of the pressure switch (YEL) and Gnd.
  • Power on One Side Only = Switch Not Closed
  • Power on Both Sides + Code 3 = Bad Control Board
• Switch Pressure
• Inspect the pressure switch tubing for a:
  • Loose hose
  • Dry-rotted, cracked hose
  • Clogged hose
• Use a pressure meter to check the pressure at the switch.
• Compare actual pressure to pressure rating on the switch.
  • Pressure near or below rating = Blocked or Restricted Vent 
  • Pressure well above rating + Switch Not Closed = Bad Switch