TM9Y - Flashing Code 4

York Gas Furnace: TM9Y

Re: Flashing Code 4

Code 4 has two possible meanings:

• Code 4 = Limit switch circuit is currently open.
  • If the limit switch circuit opens during a call for heat, the control will indicate 4 Red Flashes.
  • ► The control will operate the supply air blower and inducer while the open limit condition exists.
  • ► If the limit switch has not re-closed within five minutes, the control will assume that the blower is not functioning, will start a hard lockout and will begin to flash the 11 Red Flashes error code.
• Code 4 = Multiple limit openings during a single call for heat.
  • If the main limit switch opens five times within a single call for heat, the control will also indicate 4 Red Flashes and will enter a one-hour soft lockout.
  • ► During the one-hour soft lockout the supply air blower and inducer will remain off.

CHECKOUT:

1. Check Temperature Rise

• 1st Stage Heat
• Un-hook the thermostat wire from W2 at the furnace.
• Start the furnace with a call for heat.
• Check the temperature rise across the furnace.
• Compare the actual temperature rise to the rated temperature rise on the furnace nameplate. (typically 40 - 70 deg.)
  • Temperature Rise At or Above Maximum → Step 2. Check Air Filter
  • Temperature Rise Below Maximum and Limit Does Not Trip ⇒ Check 2nd Stage Heat (below)
  •  Temperature Rise Below Maximum + Limit Trips ⇒ Suspect Bad Limit
• 2nd Stage Heat
• Reconnect the thermostat wire to W2 at the furnace.
• Place a temporary jumper between W1 & W2.
• Start the furnace with a call for heat.
• Check the temperature rise across the furnace.
• Compare the actual temperature rise to the rated temperature rise on the furnace nameplate. (typically 40 - 70 deg.)
  • Temperature Rise At or Above Maximum → Step 2. Check Air Filter
  • Temperature Rise Below Maximum and Limit Does Not Trip → Step 6. Check Blower Off Delay
  • Temperature Rise Below Maximum + Limit Trips ⇒ Suspect Bad Limit

2. Check Air Filter

• Remove air filter and recheck temperature rise.
  • Temperature rise drops into normal range = Clogged or Restrictive Air Filter
  • Temperature rise still too high → Step 3. Check Gas Pressure

3. Check Gas Pressure

• De-energize the call for heat and allow the furnace to cool.
• Check the manifold gas pressure.
• 1st Stage Heat
  • Natural Gas = 1.5 to 2" w.c.
  • LP Gas = 6" to 8" w.c. 
• 2nd Stage Heat
  • Natural Gas = 2.5 to 3.5 " w.c.
  • LP Gas = 9" to 11" w.c. 
    • Pressure Above Maximum ⇒ Adjust Gas Pressure & Re-check Temperature Rise
    • Pressure Below Maximum + Still Over-Heating → Step 4. Check Blower Speed

4. Check Blower Speed

• Check the blower motor speed wire attached to the "Lo Heat" and "Hi Heat" outputs of the control board.
  • Red = Low
  • Yellow = Med Low
  • Gray = Med
  • Blue = Med Hi
  • Black = Hi
• If possible, increase the Heat blower speed and Re-Check Temperature Rise

5. Check Duct Static Pressure

• Check the return static pressure (in the blower door if possible).
• Check the supply static pressure (between the furnace and evaporator coil if possible).
  • High Duct Static = Above 0.5" w.c.
    • High Return Static + Low Supply Static = Restricted Return Ductwork
    • Low Return Static + High Supply Static = Clogged Coil or Restricted Supply Ductwork
      • Compare static on both sides of evaporator coil.
        • High Static Entering Coil + Low Static Leaving Coil = Clogged Coil

6. Check Blower Off Delay

• The Blower Delay Time is the amount of time the blower continues to run after the burners shut off.
  • The Default Blower Delay is set for 60 Seconds.
• There are two sets of Dip Switches above the LED Status light on the furnace control board.
  • One set has two switches for Continuous Fan Speed (CONT SPEED), and the other has four switches, (1&2 = STAGING, 3&4 = BLWR DELAY)
• In horizontal applications, it may be necessary to increase the Blower Delay.
  • Change Blower Delay to 180 Seconds (Dip Switch 3 = On, 4 = On).