Furnace attempts to start but shuts down; E4 displayed on control board

Safety: Turn off power before removing panels. Components may be hot.

• 1. Replace or clean air filter: Locate the return-air filter (often in the blower compartment or return grille). Replace disposable filters or clean washable ones. Use the correct size and airflow rating recommended for your Frigidaire furnace.
• 2. Check vents and registers: Walk through the home and ensure supply registers and return grilles are open and not blocked by furniture, rugs, or drapes.
• 3. Inspect blower operation: Remove the blower compartment door. Restore power and call for heat. Confirm the indoor blower starts on time and runs at full speed. If the motor hums, starts slowly, or stops intermittently, it may be failing.
• 4. Clean blower and cabinet: With power off, vacuum dust from the blower wheel, motor, and furnace interior. Excess dust can reduce airflow and cause overheating.
• 5. High limit switch check: Locate the high limit switch on the heat exchanger panel. Ensure wiring is secure. If the furnace overheats quickly even with good airflow, the switch may be weak and require replacement.
• 6. Call a professional: Repeated high-limit trips can indicate a cracked heat exchanger or undersized ductwork. Have a licensed HVAC technician inspect the heat exchanger and static pressure.