331-01975-102 Demand Defrost - Installation

Article ID: 100
Last updated: 10 Nov, 2020

York Heat Pump

Re: Replacement Demand Defrost Control Board - S1-33101975102


  1. Power off unit totally - 240V & 24V
    • Pull unit disconnect.
    • Disconnect high voltage power to air handler
  2. Record positions and colors of original wiring.
  3. Remove old defrost control board.
    • Phillips screws in corners.
  4. Install replacement board, utilizing original screws.
  5. Set the Defrost Curve Selection Jumper to the proper position.
    • For any new setting to take effect 24V power must be removed and reapplied.
  6. Re-attach wiring and power-up the unit - 240V & 24V.


When the control board is replaced the jumper MUST be placed in a numbered position. Select the proper jumper position.

  • Position #1 is recommended for reciprocating compressors.
  • Position #2 is recommended for scroll compressors.
  • Do not use Position #3 or 4 unless instructed to do so by technical support.

If the jumper is missing or left in the P position, the replacement control will not energize the compressor.

► When the jumper position is changed, the control will not act upon the jumper changes until the thermostat calls are de-energized or power (24VAC) to the control is cycled.

The control will display the active defrost curve using the X/L terminal when the heat pump is operating in a defrost cycle that has been forced using the TEST input. For instance, the X/L output will be energized with two flashes when defrost curve 2 is active.


When Defrost Jumper Position #2 is selected the compressor is shut down for 30 seconds entering and exiting defrost mode.

The delay is present in a normal defrost but IS NOT present when the TEST pins are shorted to initiate a defrost cycle.

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Article ID: 100
Last updated: 10 Nov, 2020
Revision: 14
Views: 329
Comments: 0
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