AHX/MX Air Handler - Flashing Code 5

York Air Handler: AHX / MX

Re: Flashing Code 5

Code 5 = Multiple Extended Limit Trips

A Fault Code 5 is generated from the following sequence of conditions:

• If the limit switch opens for a long duration (Fault Code 4), the control will energize the blower until power is removed from the control.
• If the limit switch opens for a second long duration period during a single call for heat (Fault Code 5), the control will enter a "soft lockout" which will keep the blower locked on and lockout the heat outputs for one hour.
  • After the one-hour period has passed, the control will re-energize electric heat according to the thermostat inputs using normal timings.
  • The blower will remain locked on from the first long duration limit opening.

Checkout:

1. 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

2. 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.
    • Limit Closed + Code 3 or 4 = Bad Control Board

3. Check Blower 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 Motor
    • 230VAC + No 24VAC = Bad Control Board

4. Check Heat Relays

• Make sure there is no call for auxiliary heat.
  • Remove any low voltage wiring from the White and Brown wires.
• Check amperage of each heater
  • No Call for Heat + Amperage = Stuck Heat Relay or Bad Heater Board
    • Remove the low voltage wires from the heat relay and recheck amperage.
      • Amperage Goes Away = Bad Heater Board
      • No Low Voltage + Amperage = Stuck Heat Relay