GSZ14 - Defrost Problem, Outdoor Coil Frozen

Goodman Heat Pump: SSZ14/GSZ14

Re: Defrost Problem, Outdoor Coil Frozen

The Goodman SSZ14/GSZ14 Heat Pump uses a Time & Temperature Defrost Board.

► There are two different defrost boards used on these models. 

• PCBDM101 = Simple Time & Temperature Defrost Board
• PCBDM133S = Advanced Time & Temperature Defrost Board with Extra terminals: "Cont" = Output to Contactor, "PS1" & PS2" = Pressure Switch Inputs.

CHECKOUT:

1. Check Operating Status

• If the outdoor unit is running, check for 24VAC at the contactor.
  • No Power + Unit Operating = Stuck Contactor
• If the outdoor unit is not running, set the thermostat to call for heat.
• Ensure that the compressor and outdoor fan start and run properly.
  • No Outdoor Fan Operation → Step 2. Check Fan Motor
  • Compressor & Outdoor Fan Operating → Step 3. Check Defrost Board

2. Check Fan Motor

• With the compressor operating, use a multi-meter to check for 230VAC power between the motor's Purple and Black wires.
  • No Power = Bad Defrost Board or In Defrost Mode
  • Power + No Operation ⇒ Possibly a Bad Fan Motor or Capacitor.
    • Check the physical temperature of the motor.
      • A Hot Motor = Motor may be overheated and out on its internal overload (motor may have to cool).

3. Check Defrost Board

• Check Board Power
• 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.
• Check Defrost Thermostat
• ► The Defrost Thermostat should close its contacts at 30deg and open at 60deg.
• Check for 24VAC between "C" and "R-DFT" (Red) on the defrost board.
• Check for 24VAC between "C" and "DFT" (Red) on the defrost board.
  • No Power on Either Terminal = No Power on "R" or Bad Defrost Board
  • Power on Both Terminals = Defrost Stat Closed, Ready for Defrost
  • Power on One Terminal Only = Defrost Stat Open, Not Ready for Defrost
    • Cold Coil + Open Defrost Stat = Bad or Disconnected Defrost Stat
    • Warm Coil + Open Defrost Stat ⇒ It may be necessary to temporarily bypass the stat by placing a jumper across "R-DFT" and "DFT".
• Force a Defrost Cycle by jumping the Test pins on the defrost board.
  • A defrost cycle should initiate within 5 seconds.
    • Defrost Stat Closed + No Defrost Cycle = Bad Defrost Board
    • Initiates Defrost + Terminates Quickly = Wrong Stat Location (Must be on a coil feeder line between the metering device and coil)
    • Normal Defrost Cycle ⇒ Check refrigerant pressures in defrost mode: Should come-up to approx. 300-350psi (Head) and at least 100psi (Suction) to terminate.

DEFROST MODE

• Connect a thermometer to the liquid line near the outdoor unit.
• Initiate a Defrost Cycle by jumping the TEST pins.
• Monitor system pressures and the liquid line temperature while the unit is in a defrost cycle.
• Suction and Discharge pressure should slowly climb as the coil warms.
  • Suction Pressure, Discharge Pressure and Liquid Line Temperature Don't Increase ⇒ Check Heating Refrigerant Charge pressures (below)

4. Check Heating Refrigerant Charge

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

• Blue ⇒ True Suction Pressure Port
• Red ⇒ High Pressure Port (Either refrigerant line)

• Monitor pressures as the system operates.
• ► If the outdoor coil is still frozen, suction pressures will be low.

• Low Pressure Issues
  • Low Suction + Low Discharge + 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 + High Discharge + Expansion Valve Frosting = Bad Expansion Valve