York Air Handler: AHX/MX

Re: Flashing Code 3 - Fan Running Continuous

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

If the limit switch opens multiple times during a single call for electric heat the control will flash a Code 3 and energize the blower until power is removed from the control.

The control will continue to cycle the heat outputs on and off as the limit re-closes and opens.

The constant fan operation will signal the homeowner that a problem has occurred and a service call is required.

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

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

Checkout:

1. Check Cabinet Insulation

• Open the blower compartment and look for loose insulation that could block one or both sides of the blower.
  • The most effective repair is to screw one or more metal straps the full length of the loose insulation.

2. Check for Water on Control Board

• Especially in counter-flow applications, the control board is extremely susceptible to water damage from condensate overflow.
  • If there is water in the base of the air handler, or if the control board has obvious signs of water damage ⇒ suspect a Bad Control Board

3. Check Limits & Board

• Turn off power to the air handler.
  • It is best to turn off power at the breaker box as this test may bring you into contact with the inlet power wiring.
• Disconnect the white molex plug from the air handler control board.
• On the plug (not the board) check resistance between the Red and Brown wires.
  • No Resistance Red to Brown = Open Limit
  • Resistance Red to Brown = Limit circuit closed ⇒ Re-attach molex plug and re-power air handler.
    • Still Code 3 or 4 = Bad Control Board

4. Check Blower Speeds/Operation

• Activate a call for Fan by one of the following methods:
  • At the thermostat, turn the "Fan" switch to "On".
  • At the air handler control board, place a jumper wire between "R" and "G".
• X-13 Motor (AHX/MX)
  • Check high voltage plug for 230VAC
  • Check for 24VAC between "C" and "Red" at motor.
    • 230VAC + 24VAC on Red + No Blower = Bad Blower Motor
    • 230VAC + No 24VAC = Bad Control Board

5. Check Air Filter

• With the filter in, run the unit in "Em Heat" and check the temperature rise.
• Remove the air filter and recheck the temperature rise.
  • Little or No Change = Filter (may need replaced but) Not the Cause
  • Big Change = Clogged or Restrictive Air Filter
    • Be cautious of the expensive 3M Filters from Lowes (Very Restrictive!)