Daikin furnace/air handler shows A3; unit may shut down on condensate fault, especially in high-efficiency models with PVC venting.

Safety: Turn off power to the furnace before working on the condensate system. Water around electrical components is hazardous.

Steps to check:

• Inspect drain tubing: Locate the condensate drain coming from the Daikin furnace’s secondary heat exchanger or coil pan. Check for kinks, sags filled with water, or algae buildup.
• Clean the trap: If there is a condensate trap, remove it (if accessible) and flush it with warm water and a small amount of mild bleach or vinegar to clear slime and debris.
• Check condensate pump: If a condensate pump is used, verify it has power and that the float moves freely. Pour water into the pump reservoir to see if it activates and discharges water.
• Reset float switch: Many Daikin systems wire a float switch in series with the thermostat circuit. Once water is cleared and the float drops, the A3 code should clear after a power cycle.
• Ensure proper slope: Confirm that the drain line slopes continuously downward to the drain and is securely supported.

If the A3 code persists after clearing the drain and verifying pump operation, the float switch or associated wiring may be faulty and should be tested and replaced by a technician.