Daikin A5 Error Code

What does Daikin A5 mean?

The A5 code covers two related protections: freeze-up protection in cooling and high-pressure control in heating. The indoor heat exchanger thermistor has seen a temperature outside the safe operating window, so the PCB pulls the compressor down to avoid icing the coil or tripping the high-pressure switch. Airflow restriction is the most common trigger — treat A5 as a symptom of poor heat transfer at the indoor coil.

Symptoms

• Unit runs briefly in cooling then stops with A5 and heavy frost on the indoor coil
• In heating mode, compressor ramps down and A5 displays under load
• Weak airflow from the supply grille
• Hissing or gurgling at the indoor unit
• Error clears temporarily after a filter clean then returns

Common causes

• Clogged indoor air filter or blocked return grille
• Dirty indoor heat exchanger coil restricting airflow
• Defective or shorted indoor heat-exchanger thermistor
• Indoor fan motor running slow or failing to reach commanded RPM
• Low refrigerant charge or expansion-valve malfunction

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Diagnostic steps

1. Clean or replace the indoor air filter

   Remove the filter panel, wash with warm water and mild detergent, and let dry. Replace disposable filters outright if loaded.

2. Inspect and clean the indoor coil

   Check the evaporator fin pack for dust mats or nicotine film. Brush and flush with a coil cleaner if fouled.

3. Verify indoor fan speed

   Run the unit on high fan and confirm airflow at the supply. Slow or uneven airflow points to a failing fan motor or PCB tap.

4. Test the heat-exchanger thermistor

   Disconnect the thermistor and measure resistance against the service manual R-T table at ambient. Replace if out of spec.

5. Check refrigerant charge at the gauges

   Connect manifold gauges and compare suction and discharge pressures to the charging chart for current ambient. Low charge requires leak test and recharge.

6. Replace the indoor PCB if inputs are good

   A healthy thermistor, fan, and charge with persistent A5 points to the indoor PCB misreading analogue inputs — swap the board.

When to call a professional

Call a licensed technician if cleaning the filter and coil does not clear A5, as the remaining causes involve refrigerant work and thermistor verification. Handling refrigerant requires EPA 608 or local equivalent certification, and leak-testing a split system with nitrogen plus proper evacuation is not a DIY task. A pro can also confirm whether the expansion valve is throttling correctly and whether indoor airflow meets the design CFM.