Lennox thermostat or control shows E411 high temperature limit or coil temperature fault during cooling; system shuts down to protect components.

Safety: Turn off power to the indoor unit before removing panels or working near the blower.

• 1. Replace or clean filter: Install a new Lennox-approved filter with the correct MERV rating. Overly restrictive aftermarket filters can cause airflow faults.
• 2. Open vents and returns: Ensure at least 80% of supply registers are open. Clear furniture or rugs blocking returns.
• 3. Inspect evaporator coil: Remove the coil access panel. If the coil is matted with dust or pet hair, carefully vacuum the surface and use a foaming coil cleaner suitable for indoor use.
• 4. Verify blower speed tap (PSC motors): On non-ECM systems, confirm the cooling speed tap is connected to the correct terminal on the control board per Lennox wiring diagram.

Note: If the error persists after restoring airflow, a sensor or control board issue may be present and should be checked by a technician.