York Rooftop Unit: Predator DH, DM

Re: Ignition Control - Flashing Code 6

Flashing Code 6 = Main Limit Switch Open or Aux Limit Switch Open

The main limit and auxiliary limit are wired in series. Therefore either switch open on a call for heat will generate a code 6 on the Ignition Control board.

CHECKOUT:

1. Check Ignition Control Board

• Start the furnace with a call for heat.
• At the Ignition Control Board (IC) check for 24VAC between "L" and "C".
  • Power Present + Code 6 = Bad Ignition Control Board
  • No Power = Limit circuit open → Step 2. Check Limits

2. Check Limits

• Main Limit (located under burners)
• Check for 24VAC from each side of the limit (Yel and Blu) to "C".
  • Power on One Side Only = Open Limit 
    • Open Limit + Cool = Bad Limit Switch
    • Open Limit + Hot → Step 3. Check Air Flow
  • Power on Both Sides + No Power on "L" = Broken Wire Between Main Limit & IC Board
  • No Power on Either Side ⇒ Check Aux Limit
• Aux Limit (located in blower compartment)
• Check for 24VAC from each side of the limit (Red and Blu) to "C".
  • Power on One Side Only = Open Limit ⇒ Reset and check for No Airflow
  • Power on Both Sides + No Power at Main Limit = Broken Wire Between Aux & Main Limit
  • No Power on Either Side = Broken Wire Between Main Control & Aux Limit

3. Check Airflow

• Check the blower belt.
• Check the air filters.
• Check blower motor operation.