Samsung Air Conditioner Error Code E166

E166 indicates that during the system's piping check, the evaporator inlet temperature of an indoor unit that was not being tested changed unexpectedly. This tells the controller that refrigerant is flowing through the wrong unit at the wrong time. The most common causes are an indoor unit address mismatch or an EEV that is not closing properly. The system cannot complete commissioning and enter normal operation until this error is resolved.

A power reset may temporarily clear the fault display, but E166 will return as soon as the system attempts another piping check if the underlying issue is not corrected. The piping check must complete successfully for the error to stay cleared. Address the root cause, such as fixing the unit address or EEV connection, before retrying the commissioning sequence.

If the fix is simply correcting an address setting or reseating a connector, the cost may be limited to a service call fee, typically in the range of $75 to $150. If an EEV needs to be replaced, parts and labor together can range from $200 to $500 or more depending on the unit model and local labor rates. A technician will need to diagnose the specific cause before an accurate estimate can be given.

Checking and correcting indoor unit address settings is something a knowledgeable installer or DIYer can attempt by consulting the unit's address configuration instructions. However, inspecting and testing the EEV, checking wiring harnesses inside the indoor unit, and running a new piping check typically require familiarity with multi-split systems and refrigerant circuit diagnostics. If address settings look correct, calling a qualified technician is the safer next step.

The system is designed to halt normal operation when a piping check fails, so in most cases the unit will not run in cooling or heating mode while E166 is active. Attempting to force operation without resolving the error could lead to improper refrigerant distribution and potential compressor stress. It is best to resolve the fault before resuming normal use.