Trane Package Unit: 4YCC4

Re: Flashing Code 4

Code 4 = High Limit or Roll-Out Switch Open

* After 4 limit trips during a single call for heat, the control will enter a 1-Hour Soft Lockout and flash Code 4.

CHECKOUT:

1. Check Limit Circuit

• Primary Limit (located behind the blower housing)
• On the ignition control board, check for 24VAC between PP-9 >> 37A (OR) and Gnd.
• Check for 24VAC between PP-8 >> 39A (OR) and Gnd.
  • Power on Both = Primary Limit Closed ⇒ Check Roll-Out Limit
  • Power on One Only = Primary Limit Open
    • Open Limit + Cool Heat Chamber = Bad Limit
    • Open Limit + Hot Heat Chamber → Step 2. Check Temperature Rise
• Roll-Out Limit (located on the right-hand side of the burner manifold)
• Check for 24VAC between PP-8 >> 38A (OR) and Gnd.
• Check for 24VAC between PP-6 >> 49A (PR) and Gnd.
  • Power on Both = Roll-Out Limit Closed → Step 2. Check Temperature Rise
  • Power on One Only = Roll-Out Limit Open ⇒ Manually reset the roll-out limit and check for a Bad Inducer Blower Wheel or a Bad Heat Exchanger.

2. Check Temperature Rise

• Initiate a call for heat (Reset the control if necessary by cycling power.)
• Ensure that the burners fire and the blower motor starts withing 60 seconds.
  • Burners + No Blower Operation ⇒ Check for 24VAC between 73A (PR) and Gnd after the burners light.
    • Power + No Blower = Bad Blower Motor
    • No Power = Bad Ignition Control Board
• Monitor the heat exchanger temperature rise.
  • Temperature Rise > Furnace Rating → Step 3. Check Filter
  • Temperature Rise < Furnace Rating + Limit Opens = Bad Limit

3. Check Air Filter

• Remove the air filter and re-check the temperature rise.
  • Temperature Rise Becomes Normal = Clogged or Under-Sized Air Filter
  • Temperature Rise Still > Furnace Rating → Step 4. Check Gas Pressure

4. Check Gas Pressure

• Activate a call for heat and monitor the manifold gas pressure when the gas valve opens.
  • Natural Gas = 2.5" w.c. minimum to 3.5" w.c. maximum
  • LP Gas = 9" w.c. minimum to 11" w.c. maximum
    • Pressure Below Maximum → Step 5. Check Duct Static/Blower Speed
    • Pressure Above Maximum ⇒ Lower Manifold Gas Pressure & Re-check Temperature Rise

5. Check Duct Static/Blower Speed

• Check the return static pressure (in the blower door if possible).
• Check the supply static pressure.
  • High Duct Static = Above 0.5" w.c.
    • High Return Static + Low Supply Static = Restricted Return Ductwork or Clogged Coil
    • Low Return Static + High Supply Static = Restricted Supply Ductwork
    • Normal Duct Static ⇒ Increase the blower speed by moving 73A (PR) at the motor from Terminal 4 (Med Hi) to Terminal 5 (Hi) and re-check the temperature rise.