York Air Handler: AHX/MX

Re: Flashing Code 2

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

Code 2 = Limit switch opened two times with NO CALL FOR HEAT.

• This is a Hard Lockout condition that will keep all heater outputs off.
• The blower will de-energize 5 minutes after entering Hard Lockout.

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

Checkout:

1. Check Heaters

• Open the air handler blower compartment.
• Check for 24VAC on W1 and W2.
  • Power Present ⇒ Disconnect low voltage wiring from W1 & W2,
• Check heater amperage.
  • Amperage Present → Step 2. Check Heater Board

2. Check Heater 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
• At the white molex plug on the heater board, check for 22VDC between:
  • "Purple" to "Brown
  • "Yellow" to "Brown"
  • "Gray" to "Brown"
    • No 24VAC Power on W1 or W2 + 22VDC Present = Bad Control Board

3. Check Heat Relays

• With high voltage power applied, check amperage on each heater individually.
  • No Heater Drawing Amperage → Step 4. Check Limit
  • Heater Drawing Amperage ⇒
    • Trace back to the controlling relay.
    • Remove one high voltage wire from the relay.
      • Amperage Still Present = Shorted Heater
      • Amperage Goes Away = Bad Heater Relay

4. Check Limits

• 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 Closed ⇒ Re-attach molex plug and re-power air handler.
    • Still Code 2, 3 or 4 = Bad Control Board

5. Check Compressor Contactor

• It is possible that a stuck compressor contactor could generate enough heat in the air handler to trip a heater limit.
• Check the outdoor unit for a Stuck Contactor or signs of a potentially sticking contactor.