Freeze-up protection or heating peak-cut: the indoor heat exchanger got too cold in cooling or too hot in heating.
Daikin A5 stops the unit when the indoor heat exchanger is below 32°F in cooling, or above about 140°F in heating. The manual's first checks are a short-circuited air path and a dirty indoor filter. U4 is the indoor-to-outdoor transmission error and does not use that filter step.
Likely causes
- Short-circuited air around the indoor unit
- Clogged air filter of the indoor unit
- Dust on the indoor heat exchanger
- Defective indoor heat exchanger thermistor
- Defective indoor unit PCB
How to fix A5: safe DIY steps
- Make sure supply and return air can move around the indoor unit. The manual calls a blocked path a short circuit of air
- Clean the indoor unit's washable air filter if it is dirty, with the breaker off, and put it back dry
- If A5 returns, stop. Thermistor and board checks are in the service manual
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician if a clear air path and a clean filter do not keep A5 from returning. Do not spray the coil or open the outdoor unit.
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