York Air Handler: AHP/MP
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.
Qty |
Possible Causes: |
|
Stuck Heat Relay |
|
Bad Control Board |
|
Bad Limit |
|
Shorted Heater |
|
Stuck Contactor (OD Unit) |
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.
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.