Goodman Heat Pump Won't Defrost

Article ID: 110
Last updated: 26 Jan, 2023

Goodman Heat Pump: GS13

Re: Won't Defrost

The Goodman GS13 Heat Pump uses a Time & Temperature Defrost Board.

  • A defrost thermostat mounted to the outdoor coil closes at approximately 30 deg. and opens at approximately 60 deg.
  • An adjustable setting on the board allows adjustment of the time between defrost cycles to either 30, 60 or 90 minutes.
  • When the board receives 24VAC on the "Y" terminal the timer starts. When the compressor runtime exceeds the set defrost time, and the defrost thermostat is closed, a defrost cycle will be initiated.

Qty Possible Causes:
1 Bad or Disconnected Defrost Stat
Bad Defrost Board
Stuck Contactor
Low Refrigerant Charge
Bad Cond Fan Motor / Capacitor
Mis-Located Defrost Stat
Stuck Reversing Valve
Defrost Timer Set Too Long


1. Check Operating Status

2. Check Fan Motor

  • With the compressor operating, use a multi-meter to check for 230VAC power between the motor's Black and Red wires.
    • No Power = Bad Defrost Board or In Defrost Mode
    • Power but No Operation = Bad Fan Motor or Capacitor

3. Check Refrigerant Charge

Hook-up refrigerant gauges to the pressure ports on the unit.

  • Blue ⇔"True Suction" Low Pressure
  • Red ⇔ High Pressure (either refrigerant line)
  • Monitor pressures as the system operates.
Normal Pressure Range
Refrigerant 0-30 Deg O/D 30-50 Deg O/D
  • 20-40 Suction
  • 150-225 Discharge
  • 40-75 Suction
  • 170-260 Discharge
  • 70-100 Suction
  • 250-320 Discharge
  • 100-135 Suction
  • 250-375 Discharge
  • If a Liquid-Line Sight Glass is installed, observe for bubbles in the sight glass (after the system has been operating for at least 5 min.)
    • Bubbles = Low Refrigerant Charge
  • Low Pressure Issues
    • Low Suction + Low Discharge + Bubbles in Sight Glass + Expansion Valve Frosting = Low Refrigerant Charge
      • Try adding refrigerant through the Low Pressure gauge.
        • Suction and Discharge Pressures should gradually increase as refrigerant is added.
        • If the Discharge Pressure increases but the Suction stays low or drops = Bad Expansion Valve
    • Low Suction + Low Discharge + Clear Sight Glass + Expansion Valve Frosting = Bad Expansion Valve

4. Check Defrost Board

  • Check for 24VAC between "C" and "R" on the defrost board.
    • No Power = Mis-wired Low Voltage
  • Check for 24VAC between "C" and "Y" on the defrost board.
    • No Power on "Y" + Unit Operating = Stuck Contactor
  • Check for 24VAC between "C" and "DFT" on the defrost board.
    • No Power = Defrost Stat Open (Not ready for defrost)
      • Cold Coil + Open Defrost Stat = Bad or Disconnected Defrost Stat
      • Warm Coil + Open Defrost Stat = Normal
        • ​​​​​​​It may be necessary to temporarily bypass the stat by placing a jumper across "R" and "DFT".
  • Speed-up the timer by jumping the Test pins on the defrost board.
    • A defrost cycle should initiate within 5 seconds (Outdoor Fan Stops, Reversing Valve Switches to Cool Mode, Energizes Aux Heat).
      • Power on "R" and "Y" + No Defrost Cycle = Bad Defrost Board
      • Outdoor Fan Stops + Reversing Valve Doesn't Switch = Stuck Reversing Valve, Bad Rev Valve Coil or Loose Wiring to Coil

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Article ID: 110
Last updated: 26 Jan, 2023
Revision: 15
Access: Public
Views: 1353
Comments: 0
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