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Error code reference

LG Hvac Error Code 27

Inverter compressor amperage over 100A for a split second.

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Inverter compressor amperage over 100A for a split second.

First step from the service manual

Verify proper 208/240V AC feeding unit, ensure not in high-head situation, verify 3 compressor windings all equal at 1-4Ω, verify ∞Ω to ground, check amperage, check reactor connections and verify reactor resistance is less than 1Ω.

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

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What 27 means on a LG hvac

Error code 27 on an LG inverter-driven HVAC system indicates that the inverter compressor drew an amperage spike exceeding 100 amps, even if only momentarily. The inverter drive board monitors compressor current in real time, and when current surges to this extreme level the system shuts down to protect the compressor windings, the inverter module, and the power circuit components. A spike of this magnitude points to either an electrical supply problem, a mechanical load problem inside the compressor, or a fault in the drive circuitry itself.

The most important first checks involve the power supply and the compressor's electrical integrity. The unit requires a stable 208/240V AC input, and a low or unbalanced supply voltage can force the inverter to draw excessive current trying to maintain compressor speed. The compressor windings themselves must be verified: all three windings should measure between 1 and 4 ohms relative to each other and should show infinite resistance to ground. Any winding that reads outside these values points to a failed compressor. A high-head pressure situation, caused by a dirty outdoor coil, blocked airflow, or refrigerant overcharge, dramatically increases the mechanical load on the compressor and can trigger this current spike.

The reactor, which is an inductor wired in series with the compressor circuit to smooth inverter output current, is another critical component to inspect. Its resistance should measure below 1 ohm. A loose reactor connection or an open reactor can disrupt current flow and cause erratic amperage behavior that triggers error 27. All reactor wiring terminals should be checked for tightness and signs of arcing or heat damage before replacing any major components.

Source: manufacturer service documentation.

Common causes of 27

  1. 01

    High head pressure condition

    Wiring / connection

    A blocked or dirty outdoor coil, restricted airflow around the unit, or refrigerant overcharge increases compressor mechanical load drastically, causing current to spike above 100A. Check outdoor coil cleanliness and ensure the unit has adequate clearance on all sides.

  2. 02

    Low or unbalanced supply voltage

    Wiring / connection

    Insufficient or unstable 208/240V AC input forces the inverter to compensate by drawing higher current, which can produce extreme momentary spikes. Measure voltage at the unit's terminal block under load to confirm the supply is within spec.

  3. 03

    Failed or degraded compressor windings

    Part replacement

    If any of the three compressor windings read outside the 1 to 4 ohm range or show any continuity to ground instead of infinite resistance, the compressor has failed internally and is drawing excessive current. This requires compressor replacement.

  4. 04

    Loose or failed reactor connections

    Part replacement

    The reactor is wired in series with the compressor to smooth inverter current output, and its resistance must be below 1 ohm. Loose terminals or an open reactor disrupts current regulation and can cause the spike that triggers error 27. Inspect all reactor wiring connections for looseness, arcing, or heat damage.

  5. 05

    Faulty inverter drive board

    Part replacement

    If the power supply, compressor windings, reactor, and head pressure all check out correctly, the inverter board itself may be misreading or generating abnormal current output. This requires board-level diagnosis or replacement.

See the test procedure for each cause

Frequently asked questions about 27

What does 27 mean on a LG hvac?
Error code 27 means the inverter compressor experienced an amperage spike exceeding 100 amps, even if only for a fraction of a second. The system shuts down automatically to protect the compressor and inverter components from damage. This code points to issues with the power supply, compressor condition, airflow restriction, or the reactor component in the drive circuit. A full electrical and mechanical inspection is required before restarting the unit.
Can I fix error code 27 on my LG HVAC myself?
Some causes, like clearing debris from around the outdoor unit to restore proper airflow, can be handled without specialized tools. However, checking compressor winding resistance, measuring supply voltage under load, and testing reactor resistance all require a multimeter and knowledge of inverter-driven systems. Compressor replacement and inverter board diagnosis should be handled by a certified HVAC technician due to the high voltages and refrigerant handling involved.
Is it safe to keep running my LG unit when error code 27 appears?
No. The system shuts itself down specifically to prevent further damage when this error occurs, and attempting to force it to run would risk destroying the compressor, the inverter board, or both. The root cause of the 100A spike must be identified and corrected before the unit is returned to service. Operating with this fault unresolved could also create a fire or electrical hazard.
Will resetting the unit clear error code 27?
A reset may temporarily clear the error and allow the unit to restart, but if the underlying cause is still present the code will return, often immediately. In cases of a compressor winding failure or a serious power supply problem, repeated restarts can cause additional damage. The error should be diagnosed and resolved before relying on a reset as a solution.
How much does it cost to repair error code 27 on an LG HVAC?
Repair costs vary widely depending on the root cause. If the fix is simply cleaning the outdoor coil or tightening reactor connections, labor costs alone may be in the range of $100 to $300. A reactor replacement typically adds $50 to $200 in parts. Compressor replacement is the most expensive outcome and can range from $1,000 to $3,000 or more depending on the system size and installation complexity. An inverter board replacement generally falls somewhere between those two extremes.

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