Furnace LED shows code 44 (secondary or auxiliary limit switch open). The furnace may run briefly, then shut down, while the blower continues to operate.

Safety first: Turn off power. Overheating can damage components and create a fire risk.

• Check airflow restrictions above the furnace: If your Carrier furnace has an A-coil or evaporator coil on top, remove the access panel (if present) and inspect for heavy dust or ice buildup. A severely clogged coil needs professional cleaning.
• Inspect return air: Ensure return grilles are not blocked and that the return duct is not collapsed or disconnected.
• Locate auxiliary limits: These are usually mounted on the blower housing or near the coil. Some are manual reset; press the red button if present.
• Filter check: Replace any dirty filters that may be causing high static pressure.

If the auxiliary limit continues to open, have a technician measure static pressure and inspect the duct system and coil.