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Error code reference

LG Air Conditioner Error Code 59

Slave outdoor unit mixed installation

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What the 59 error code actually means

Error 59 means your LG multi-unit air conditioning system has detected that two different generations of outdoor units are connected together, and they are not compatible with each other. Think of it like connecting devices that speak different languages: the system cannot coordinate properly and shuts down the connection to protect itself. A technician will need to inspect the outdoor units and replace the mismatched unit with one that matches the rest of the system.

Diagnostic procedure

The full 59 procedure

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1
First diagnostic step
Verify if 3 or more units are installed and check if both LGDC slave and super sub units are present.
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Most common causes of 59

Ranked by how often they cause this code
  1. 1Mixed-generation outdoor unit installation
  2. 2Replacement unit of incorrect generation installed
  3. 3System expansion using mismatched add-on unit
  4. 4Incorrect communication address configuration

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Questions people ask about 59

What does 59 mean on a LG air_conditioner?
Error code 59 on an LG multi-zone air conditioner indicates a slave outdoor unit mixed installation conflict. The system has detected that an older-generation super sub outdoor unit and a newer LGDC slave outdoor unit are connected together in the same network. This combination is not supported, and the system will not operate normally until the incompatible unit is replaced with one of the correct generation.
Will resetting my LG air conditioner clear error code 59?
No, resetting the system will not clear error 59. The fault is caused by a physical incompatibility between the installed outdoor units, and the system will re-detect the mismatch and re-trigger the error every time it powers on or performs its communication check. The underlying hardware mismatch must be corrected before the error will clear.
How much does it cost to fix error code 59 on an LG multi-zone system?
The cost depends primarily on which outdoor unit needs to be replaced and the labor involved in disconnecting and reinstalling a unit in a multi-zone system. Replacement outdoor units for multi-zone systems can range from several hundred to several thousand dollars depending on capacity and model. Labor costs for this type of replacement, including refrigerant handling and system recommissioning, typically add several hundred dollars on top of the parts cost.
Can I fix error code 59 myself on my LG air conditioner?
Error 59 is a hardware compatibility issue that requires identifying which outdoor unit is the incorrect generation and replacing it with a compatible unit. This is not a setting or configuration fix that can be performed without technical knowledge of LG multi-unit systems. A qualified HVAC technician with access to LG's multi-unit compatibility specifications should handle the diagnosis and unit replacement.
Is it safe to run my LG air conditioner while error code 59 is active?
The system triggers error 59 specifically to prevent operation under incompatible conditions, so normal cooling or heating output will be unavailable or unreliable while this fault is active. Attempting to force operation with mismatched outdoor units risks poor capacity control, compressor coordination failures, and potential equipment damage. The system should remain off until the incompatible unit is replaced.

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