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Error code reference

Samsung Air Conditioner Error Code E166

Change of EVAP IN temperature of other indoor unit detected during piping check.

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Change of EVAP IN temperature of other indoor unit detected during piping check.

First step from the service manual

Check indoor unit address matches MCU; check EEV connection.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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  • Wiring diagram references and connector pinouts from the OEM service manual
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What E166 means on a Samsung air conditioner

Error code E166 on a Samsung air conditioner occurs during the piping check phase, which is an automated commissioning process the system runs to verify refrigerant circuit integrity and proper indoor unit connectivity. During this check, the system monitors the evaporator inlet (EVAP IN) temperature sensor readings from each indoor unit in sequence. E166 triggers when the system detects a temperature change at the EVAP IN sensor of an indoor unit other than the one currently being tested, indicating that refrigerant flow is affecting a unit it should not be affecting at that moment.

The most likely root causes involve address configuration mismatches between an indoor unit's assigned address and what the main control unit (MCU) expects, or a problem with the Electronic Expansion Valve (EEV) on one of the indoor units. If an indoor unit address is incorrectly set, the MCU cannot accurately coordinate which unit's EEV should be open or closed during the piping check sequence, causing unintended refrigerant flow through the wrong evaporator coil and triggering this error. An EEV that is stuck open, failing to close fully, or disconnected from its control board will similarly allow refrigerant to pass through an unintended circuit.

Diagnosis should begin by verifying that every indoor unit's address setting matches the address recognized by the MCU. Following that, inspect the EEV wiring harness connections on each indoor unit for loose pins, corrosion, or damaged connectors. If connections are secure and addressing is correct, the EEV itself may require testing or replacement. The piping check must complete successfully before the system can transition to normal operation.

Source: manufacturer service documentation.

Common causes of E166

  1. 01

    Indoor unit address mismatch

    Wiring / connection

    If the address configured on an indoor unit does not match what the MCU expects, the system cannot properly sequence the piping check and may detect unintended temperature changes in the wrong unit. Verify each indoor unit's DIP switch or address setting against the system wiring diagram.

  2. 02

    EEV disconnected or wiring fault

    Wiring / connection

    A loose, corroded, or disconnected EEV wiring harness prevents the MCU from commanding the valve to close during the piping check, allowing refrigerant to flow through an unintended evaporator coil. Inspect the EEV connector and harness on each indoor unit for damage or poor contact.

  3. 03

    Faulty or stuck-open EEV

    Part replacement

    An Electronic Expansion Valve that is mechanically stuck in an open position will allow refrigerant flow even when commanded closed, causing the EVAP IN sensor on that unit to register a temperature change out of sequence. The EEV will need to be tested and likely replaced.

  4. 04

    EVAP IN temperature sensor fault

    Part replacement

    A faulty or poorly positioned evaporator inlet temperature sensor may report false temperature changes during the piping check, triggering E166 even if refrigerant flow is correct. Check the sensor's resistance value against specifications and confirm it is properly seated on the refrigerant line.

  5. 05

    MCU communication or configuration error

    Wiring / connection

    Incorrect system configuration in the MCU, such as an incorrect indoor unit count or group assignment, can cause the piping check to evaluate the wrong unit at the wrong time. Review the MCU setup parameters and confirm the total number of indoor units registered matches the physical installation.

See the test procedure for each cause

Frequently asked questions about E166

What does E166 mean on a Samsung air_conditioner?
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.
Can I fix E166 myself, or do I need a technician?
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.
Will resetting the system clear the E166 error?
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.
Is it safe to run the air conditioner with E166 active?
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.
How much does it cost to repair a Samsung air conditioner showing E166?
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.

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