Goodman Gas Furnace: GMH95 / GCH9

Re: Flashing Code 3

Code 3 = Pressure Switch failed to close with the inducer energized.

► There are 2 Pressure Switches in the furnace.  Only the Inducer Pressure Switch will cause a Code 3. The Drain Pressure Switch (labeled as Front Cover Switch) breaks power to the gas valve.

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

CHECKOUT:

1. Check Control Board / Inducer Motor

• Start the furnace with a call for heat.
  • Inducer motor should start within 15 seconds.
    • Inducer motor starts & runs normally → Step 2. Check Pressure Switch
    • Inducer motor hums but does not start = Bad Inducer Motor or Item in Inducer ⇒ Remove inducer & check
    • Inducer motor does not attempt to start & shows Code 3 ⇒ Check for 115V power to inducer.
      • Power + No Inducer = Bad Inducer Motor
      • No Power = Bad Control Board

2. Check Pressure Switch

• Switch Contacts
• Check for 24VAC between each side of the pressure switch (YEL) to C and (Org) to C.
  • Power on One Side Only = Switch Open ⇒ Check Switch Pressure
  • Power on Both Sides + Code 3 = Bad Control Board
• Switch Pressure
• 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/Restricted Vent or Bad Inducer Blower Wheel
  • Pressure Well Above Rating + Switch Not Closed = Bad Switch