Daikin furnace/air handler shows A5; unit may shut down shortly after starting, often on high heat or with restricted airflow.

Safety: Turn off power before removing panels or filters. Components may be hot immediately after shutdown.

Steps to check:

• Replace or clean filter: Remove the furnace filter and inspect it. If it is dirty or collapsed, replace it with a new filter of the correct size and MERV rating recommended by Daikin.
• Open registers: Walk through the home and open all supply and return registers. Remove any rugs or furniture blocking airflow.
• Check blower operation: With power restored and a call for heat, observe whether the Daikin ECM blower motor starts and ramps up. If the blower does not run or runs weakly, the motor or control may be failing.
• Inspect indoor coil: If accessible, inspect the underside of the evaporator coil above the furnace for heavy dust or pet hair buildup. A technician may need to remove the coil panel to clean it properly.

After restoring airflow, reset power to clear the A5 code. If the code returns, a technician should verify blower CFM, temperature rise across the furnace, and the operation of the overheat sensors.