Daikin Air Conditioner Error Code U3

The U3 code means the unit was started without completing the required check operation, which is a commissioning procedure that must be performed before a Daikin system is placed into regular service. This code is not a hardware failure but a procedural flag indicating the system has not been properly commissioned. It commonly appears after a new installation, refrigerant service, or control board replacement. A technician can resolve it by pressing and holding button BS4 on the service PCB for 5 seconds to initiate the check operation.

No, a simple power reset will not clear the U3 error. The code will return because the underlying condition, the incomplete check operation, has not been addressed. The only way to resolve U3 is to complete the check operation using the BS4 button on the service PCB. Power cycling without completing this procedure will result in the unit displaying U3 again once it restarts.

Because U3 is typically a procedural issue rather than a parts failure, the cost is usually limited to a service call fee for a technician to complete the check operation. Service call rates generally range from $75 to $200 depending on location and provider. If the code was triggered by a prior repair such as a board replacement or refrigerant recharge, the recommissioning may be included as part of that service. No replacement parts are typically needed to resolve U3 on its own.

To fix U3, the check operation must be completed by pressing and holding the BS4 button on the service PCB for at least 5 seconds. This initiates a diagnostic commissioning sequence the system requires before operating normally. Because this involves accessing the service PCB inside the unit, it should be performed by a qualified HVAC technician. Before running the check operation, verify that all wiring and refrigerant connections are correct to avoid triggering additional fault codes during the procedure.

A U3 error means the unit has not been fully commissioned, so it may operate in a restricted or unverified state. Running the system without completing the check operation means its refrigerant charge, wiring, and configuration have not been confirmed as correct. This could result in reduced efficiency or potential issues going undetected. It is advisable to have the check operation completed promptly rather than continuing to run the unit in an uncommissioned state.