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York Air Handler - Disable Limit Monitoring - Code 3

Article ID: 121
Last updated: 29 Aug, 2017

York Air Handler: MP, MX, MV, AHP, AHX, AVY

Re: Disable Code 3

The control board in the air handler monitors the limit switch in the aux heaters.

If the limit trips 3 times during a single heating cycle the board will go into a lockout and flash a code 3. This causes the fan to run continuous (even with thermostat off) and de-energizes the heating outputs.

  • The diagnostic will NOT flash or provide any indication at the thermostat.

To reset: Line or Low Voltage Power to the air handler control board must be cycled.


AS A LAST RESORT it is possible to disable the board's limit monitoring without disrupting the limit shut-down of the heaters.

Be sure to check all other low airflow possibilities before performing this operation!


The BROWN wire on the 6-wire plug of the heater board provides limit monitoring.

Cutting and splicing the BROWN wire with the RED wire as shown below keeps all limits in series without allowing a Code 3 on the board.

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Article ID: 121
Last updated: 29 Aug, 2017
Revision: 8
Views: 81
Comments: 0
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