AHP/MP Air Handler - Flashing Code 3

York Air Handler: AHP/MP

Re: Flashing Code 3

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

Code 3 = Limit switch opened multiple times during a single call for electric heat.

► The control will energize the blower until power is removed from the control.

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

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

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

4. 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".
• PSC Motor (AHP/MP)
  • Check for 230VAC between "WHT" and "?" at motor.
    • 230VAC + No Blower = Bad Motor or Capacitor
    • No 230VAC = Bad Control Board

5. Check Air Filter

• With the old filter in, run the unit in "Em Heat" and check the temperature rise.
• Replace the air filter (if dirty) and recheck the temperature rise.
  • Little or No Change = Filter (may need to be replaced but) Not the Cause
  • Big Change = Clogged Air Filter