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Error code reference

LG Hvac Error Code 1

PCB sees IDU pipe or air thermistor as open or shorted (varies by unit type

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PCB sees IDU pipe or air thermistor as open or shorted (varies by unit type: Inverter, 10/13 SEER, PTAC).

First step from the service manual

Ohm thermistor in water, measure water temperature. Pipe=2,800Ω at 38°C/100°F & 10,000Ω at 10°C/50°F. Air=5,600Ω at 38°C/100°F & 20,700Ω at 10°C/50°F. With perfect thermistor & plug connection, change PCB.

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

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What 1 means on a LG hvac

Error code 1 on LG HVAC systems indicates that the main PCB (printed circuit board) has detected an open or short circuit condition in either the indoor unit (IDU) pipe thermistor or the air thermistor. The specific thermistor involved and the exact fault behavior can vary depending on unit type, including Inverter, 10/13 SEER, and PTAC models. Thermistors are negative temperature coefficient (NTC) resistive sensors: as temperature rises, their resistance drops. When the PCB reads a resistance value outside the expected range, it interprets this as either an open circuit (infinite resistance, wire break or disconnected plug) or a short circuit (near-zero resistance, damaged sensor or wiring).

The pipe thermistor monitors refrigerant line temperature and is used by the control board to regulate compressor operation and prevent freeze-up or overheating. The air thermistor monitors return or supply air temperature and informs the system's thermostat logic. For accurate diagnosis, both thermistor types have specific resistance targets: the pipe thermistor should read approximately 2,800 ohms at 38 degrees C (100 degrees F) and 10,000 ohms at 10 degrees C (50 degrees F). The air thermistor should read approximately 5,600 ohms at 38 degrees C (100 degrees F) and 20,700 ohms at 10 degrees C (50 degrees F). Testing requires immersing the thermistor in water of a known temperature while measuring resistance with a multimeter.

If the thermistor measures within spec and the plug connection to the PCB is clean and secure, the fault lies with the PCB itself, which will need to be replaced. Wiring harness damage, corrosion at connector pins, or physical damage to the thermistor bead are the most common root causes before escalating to a board-level diagnosis.

Source: manufacturer service documentation.

Common causes of 1

  1. 01

    Failed thermistor (open or shorted sensor)

    Part replacement

    The thermistor bead itself has failed, producing a resistance value far outside the expected range. Testing the sensor in water at a known temperature and comparing the resistance reading to spec values will confirm this.

  2. 02

    Loose or disconnected thermistor plug

    Wiring / connection

    The connector between the thermistor and the PCB may have vibrated loose or was not fully seated, causing the board to read an open circuit. Inspect and reseat all thermistor connectors at the PCB before further testing.

  3. 03

    Damaged thermistor wiring harness

    Part replacement

    Chafing, pinching, or rodent damage to the wire leads between the thermistor and PCB can cause intermittent or permanent open/short faults. Visually inspect the full length of the harness for breaks, melted insulation, or corrosion.

  4. 04

    Corroded or contaminated connector pins

    Wiring / connection

    Moisture intrusion into the indoor unit can corrode the thermistor connector pins, increasing resistance or breaking the circuit entirely. Clean or replace the connector if pin corrosion is visible.

  5. 05

    Faulty PCB

    Part replacement

    If the thermistor tests within its specified resistance values at a known temperature and the connector is in good condition, the PCB's thermistor input circuit has likely failed. Board replacement is required in this scenario.

See the test procedure for each cause

Frequently asked questions about 1

What does 1 mean on a LG hvac?
Error code 1 on an LG HVAC system means the control board has detected that the indoor unit pipe thermistor or air thermistor is reading as open or shorted. This applies to Inverter, 10/13 SEER, and PTAC unit types. The system cannot accurately monitor temperatures without a functioning thermistor, so it generates this fault code and may stop operating normally. A technician will test the thermistor's resistance against known specification values to determine whether the sensor, wiring, or PCB is at fault.
Can I fix error code 1 on my LG HVAC myself?
A knowledgeable DIYer can perform basic checks such as reseating thermistor connectors and inspecting the wiring harness for visible damage. Accurate diagnosis also requires a multimeter and a water bath test to compare thermistor resistance against the specified values at a known temperature. However, if the PCB needs replacement, that repair is more involved and may be better suited for a qualified technician familiar with LG systems.
Is it safe to keep running my LG HVAC with error code 1 active?
Continuing to operate the unit with error code 1 active is not recommended. Without a functioning thermistor, the PCB cannot accurately monitor refrigerant line or air temperatures, which can lead to issues such as coil freeze-up, compressor damage, or improper cooling and heating cycles. The system may shut itself down automatically as a protective measure.
Will resetting my LG HVAC clear error code 1?
A power reset may temporarily clear the fault display, but error code 1 will return as soon as the PCB re-reads the faulty thermistor or broken circuit. Resetting the unit does not address the underlying hardware problem. The thermistor, its wiring, and the PCB connection all need to be tested and repaired before the code will clear permanently.
How much does it cost to repair error code 1 on an LG HVAC?
Repair costs depend on which component has failed. A replacement thermistor is typically an inexpensive part, with the overall repair cost including labor often ranging from around $75 to $200. If the PCB is at fault, parts and labor costs can range from $200 to $600 or more depending on the model and local labor rates. Getting a diagnostic visit from a technician will give you a firm estimate before committing to the repair.

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