Goodman Heat Pump: GS13

Re: Time & Temperature Defrost Board

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.

Defrost Cycle

During a defrost cycle, the control board does the following:

• Sends 24VAC to the reversing valve to switch into cooling mode.
• Stops the outdoor fan by energizing the onboard fan relay and breaking ole leg oh high voltage power to the fan.
• Sends 24VAC out the "W2" terminal to energize the electric heaters in the air handler. 

Force a Defrost Cycle

If the defrost thermostat is closed, you can force a defrost cycle by shorting the "Test" pins on the defrost board.

Shorting the Test pins does not immediately activate a defrost cycle but, instead, speeds-up the timer in the board.

• Remove the jumper once defrost initiates.
• The defrost cycle will terminate when the defrost thermostat re-opens, the defrost timer expires or the indoor thermostat satisfies.

Test Defrost Board

1. Make sure the board is getting power.
   • Check for 24VAC between "R" and "C" on the board.
2. Make sure the thermostat is calling for compressor.
   • Check for 24VAC between "Y" and "C" on the board.
3. Make sure the defrost thermostat is closed.
   • Check for 24VAC between "DFT" and "C" on the board.
   • If the outdoor temperature is below 30 deg and the heat pump is running, the defrost thermostat should be closed or it is faulty.
   • If the outdoor temp is too warm, it may be necessary to place a jumper between "R" and "DFT" to simulate a closed defrost thermostat.
4. See if the board will initiate a defrost.
   • Move the jumper from one of the Time positions to the Test position.
   • Give the board at least 5 seconds to initiate defrost.
   • If the board fails to initiate defrost, re-test Steps 1-3.
     • Voltage present at all three points and no defrost would indicate a bad defrost board.

While in Defrost:

1. Make sure the reversing valve switches.
2. Make sure the outdoor fan stops.
3. Make sure W2 energizes.
   • Check for 24VAC between "W2" and "C" on the board.
   • Also a good idea to make sure that the heaters function.