Package Unit: YCY_F

Re: Heating - Code 4

Code 4 = High Limit Switch Open

► The F-Series (2 thru 4 Ton Models) of the YCY package units utilize a standard, PSC Blower Motor that is controlled by the Ignition Control Board (IGN). The 5 Ton model uses 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 3. Check Limit Switch
  • No Airflow Present --> Set the thermostat Fan switch to "On"
    • Still no Airflow --> Step 2. Check Blower Motor

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 IGN Board.
  • No Power = No Call from the Thermostat
• Check for 230V at the Fan Terminal Block (FTBA) from the "Red" wire to the "Black" and "Blue" wires.
  • No 230V Present = Bad Ignition Control Board
  • 230V Present at FTBA + No Blower Operation = Bad Blower Motor or Bad Capacitor

3. Check Limit Switch

• Set the thermostat to call for heat.
• Check for 24VAC between "Gnd" and "R" on the IGN.
  • No Power = No Power from Transformer
• Check for 24VAC between "Gnd" and "W1" on the IGN (1st Stage Heat).
  • No Power on "W1" = No signal from thermostat
  • Power on "W1" + IGN Flashing Code 4 = Limit Open (Blower should be running)
• 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).

4. 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 IGN.
  • 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 --> Check Air Filter & Indoor Coil
  • Lower than Rated Temperature Rise + Limit Opens = Bad Limit Switch