Package Unit: YCY_G

Re: Heating - Code 4

Code 4 = High Limit Switch Open

► The G-Series of the YCY package units utilize a Variable Speed Blower and an ICM Control Board.

CHECKOUT:

1. Check Blower Operation

• Make sure the thermostat is set correctly and calling for Heat.
• Check to see if sufficient air flow is coming from the supply registers.
  • Airflow Present --> Step 4. Check Limit Switch
  • No Airflow Present --> Set the thermostat Fan switch to "On"
    • Still no Airflow --> Step 2. Check Blower Motor
    • Airflow with Fan "On" only --> Step 3. Check Ignition Control Board

2. Check Blower Motor

• If not already, set the thermostat Fan switch to the "On" position.
• Check for 24VAC power between "Gnd" and "G" on the ICM Board.
  • No Power = No Call from the Thermostat
• Check the ICM Board for the Green "Fan" light.
  • Power Present on "G" + No "Fan" Light = Bad ICM Board
• Check for 230V across the "Red" and "Black" wires of Fen Terminal Block (FTBA).
  • 230V Present on FTBA + ICM "Fan" Light On + No Blower Operation = Bad Blower Motor

3. Check Ignition Control Board (ICB)

• Set the thermostat to call for heat.
• Check for 24VAC between "Gnd" and "R" on the ICB.
  • No Power = No Power from Transformer
• Check for 24VAC between "Gnd" and "W1" on the ICB (1st Stage Heat).
  • No Power on "W1" = No signal from thermostat
  • Power on "W1" + ICB Flashing Code 4 = Limit Open (Fan outputs should be energized)
  • Power on "W1" + ICB Fast Flash = Wait 30 seconds after burners ignite for fan outputs.
• Check for 24VAC between "Gnd" and "Indoor Blower Lo" on the ICB.
• Check for 24VAC between "Gnd" and "Indoor Blower Hi" on the ICB.
  • 24V Power on "W1" + No Power on Indoor Blower "Hi" or "Lo" = Bad Ignition Control Board (ICB) 
  • 24V Power on Indoor Blower "Hi" or "Lo" + No Blower = Bad Blower Motor or Bad ICM Control Board

4. Check Limit Switch

• Set the thermostat to call for heat.
• Check for 24VAC between "Gnd" and "R" on the ICB.
  • No Power = No Power from Transformer
• Check for 24VAC between "Gnd" and "W1" on the ICB (1st Stage Heat).
  • No Power on "W1" = No signal from thermostat
  • Power on "W1" + ICB Flashing Code 4 = Limit Open (Fan outputs should be energized)
• With the blower motor operating, check the discharge air temperature from the unit.
  • Cool Air Temperature + Limit Still Open = Bad Limit Switch
  • High Air Temperature --> Allow the furnace to cool (limit should reset).

5. Check Temperature Rise

• Set the thermostat to call for full heat.
• With the blower operating, check the return air temperature entering the unit.
• Check for 24VAC between "Gnd" and "W2" on the ICB.
  • No Power = Thermostat not calling for 2nd Stage
• With the furnace operating in 'Full-Fire", check the supply air temperature leaving the unit.
• Compare the actual temperature rise with the nameplate rated temperature rise.
  • Higher than Rated Temperature Rise = Low Airflow or Gas Over-Fired
  • Lower than Rated Temperature Rise + Limit Opens = Bad Limit Switch