White Rodgers 21V51U-843 Universal Two-Stage HSI Integrated Variable Speed (ECM) Furnace Control Kit

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This easy to install kit includes everything you need for quick and accurate replacement of all White Rodgers 50V51-XXX's and 50V61-XXX's. Simplifies stocking, installation and ensures peak system performance. 

Kit Includes:

  • Ignition Control Module
  • Wiring Harnesses for Amana/Goodman
  • Universal 120V Nitride Ignitor Kit - 21D64-2
  • Installation Instructions and OEM Cross-Reference


  • 16-pin variable speed circulator output for ECM (Electronically Commutated Motor)
  • Pushbutton fault history retrieval
  • Furnace status LED - tri-color (green, red and amber)
  • Heat fan OFF delay (dipswitch selectable)
  • Fan ON delay for cooling
  • Auto second stage delay (dipswitch selectable)
  • 120 VAC igniter output
  • 120 VAC humidifier output
  • 120 VAC electronic air cleaner output
  • 120 VAC two-speed inducer output
  • 2-Stage Gas Valve Output
  • OEM Application - Dipswitch Selectable
  • Fuse Protection - 3 Amp
  • CFM LED - (Green)
  • YLO, Y, W, W2, R, G, C, O, BK/DS/Dehum Terminals
  • Pressure Switch Inputs and Monitoring
  • Flash Microprocessor with Non-Volatile Memory
  • Flame Current Measurement Points

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  • 5
    Emerson 21V51U-843 Furnace Controller Kit

    Posted by Unknown on 29th Jan 2017

    I purchased the 21V51U-843 Furnace Control Kit to replace the original 50A51-507 Furnace Controller in my Trane XV 80 Furnace. The installation was pretty straight forward with the only modification required was drilling 2 additional 3/16” mounting holes into the bracket that supports the controller. I also removed the original 3A fuse with a short wire attached as it was redundant to the one that is now located onto the new controller. The new controller has most of its connectors in different locations and orientations so care must be taken in transferring controllers. Also, the thermostat terminal strip has some of its designations changed and in different locations. Care must be taken to insure that the interface wires are all connected to the proper terminals. All of the original wires and connectors were used with no modification and the end result was a clean install. In addition, care must be taken regarding all of the switch settings to insure proper operation similar to the old controller. I also replaced the original Ignitor with the 21D64-2 HotRod Ignitor provided with the Furnace Control Kit.

    The 21V51U-843 performed great with no apparent issues. One new feature is the tri-color LED used for status and diagnostics. The controller documentation covers the use of this LED which can be used for current status and any required trouble-shooting. In addition, there is a green LED that provides status on the Circulator, including the air-flow rate.

    I highly recommend the 21V51U-843 Kit as a replacement/upgrade to the 50A51-507 Controller.
    I would also like to state that Discount Plumbing Outlet was easy to work with and shipped very quickly.