Daikin Air Conditioner Error Code A0

The A0 code on a Daikin air conditioner indicates an error in the external protection device circuit. Specifically, the control board has detected either an open circuit or a short circuit at terminals T1 and T2 on the indoor unit terminal block. The unit shuts down when this fault is detected to prevent potential damage. Resolving it requires inspecting the wiring and any external device connected to those terminals, or installing a jumper if no device is used.

The unit will not operate normally while the A0 fault is active, as the control board shuts down the system when this error is detected. Attempting to repeatedly reset and restart without correcting the underlying wiring or device fault is not recommended. Address the root cause at the terminal block before returning the unit to service.

Repair costs depend on the cause. If only a jumper wire is needed at terminals T1 and T2, the fix may cost very little beyond a service call fee, which typically ranges from $75 to $150. Replacing a failed external protection device such as a flow switch or freeze stat can add $50 to $200 or more in parts depending on the device. If the indoor unit control board requires replacement, expect total costs in the range of $300 to $700 including labor.

Start by locating terminals T1 and T2 on the indoor unit terminal block and checking whether an external protection device is connected. If no external device is installed, install a jumper wire between T1 and T2 to close the circuit. If a device is connected, test it and its wiring for continuity and proper operation using a multimeter. Once the open or short circuit condition is corrected, the fault should clear.

A power reset may temporarily clear the A0 code, but the fault will return if the open or short circuit condition at terminals T1 and T2 has not been corrected. Resetting without fixing the cause is not a lasting solution. The error will only stay cleared once the circuit across T1 and T2 reads correctly, either through a properly functioning external device or a correctly installed jumper wire.