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Error code reference

LG Hvac Error Code 45

PCB sees ODU condenser coil middle or exit pipe (liquid line) thermistor as open or shorted.

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PCB sees ODU condenser coil middle or exit pipe (liquid line) thermistor as open or shorted.

First step from the service manual

Must be 2,800Ω at 38°C/100°F & 10,000Ω at 10°C/50°F. Ohm thermistor in water; 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 45 means on a LG hvac

Error code 45 on an LG HVAC outdoor unit indicates that the main PCB (printed circuit board) has detected a fault in the condenser coil thermistor circuit. This thermistor monitors temperature at either the middle or exit point of the condenser coil, which is also referred to as the liquid line sensor. The PCB continuously reads resistance values from this thermistor to track refrigerant and coil temperatures during operation. When the resistance reading falls outside the expected range, the board interprets the sensor as either open (infinite resistance, indicating a broken wire or failed sensor element) or shorted (near-zero resistance, indicating an internal short within the thermistor itself).

The correct resistance values for a properly functioning thermistor are approximately 10,000 ohms at 10 degrees Celsius (50 degrees Fahrenheit) and 2,800 ohms at 38 degrees Celsius (100 degrees Fahrenheit). The recommended diagnostic approach is to disconnect the thermistor and test it directly in water at a known temperature using a calibrated multimeter. This method provides an accurate ambient-temperature reference and eliminates variables caused by the surrounding air. A reading that matches these reference values confirms the thermistor itself is within specification.

If the thermistor resistance tests correctly and the connector and wiring show no visible damage, corrosion, or continuity faults, the fault lies within the PCB itself, which is misreading a good signal. In that scenario, replacing the PCB is the appropriate corrective action. However, PCB replacement should only be pursued after fully ruling out the thermistor and its associated wiring harness, as a faulty sensor or corroded plug is a far more common and cost-effective repair.

Source: manufacturer service documentation.

Common causes of 45

  1. 01

    Failed condenser coil thermistor

    Part replacement

    The thermistor element itself has degraded or failed, causing resistance to read outside the expected range. Testing the sensor in water at a known temperature and comparing against the 2,800 ohm at 38°C and 10,000 ohm at 10°C reference values will confirm this.

  2. 02

    Corroded or loose thermistor connector

    Wiring / connection

    Moisture and heat cycling in the outdoor unit can corrode the plug connection between the thermistor wiring harness and the PCB, causing intermittent or complete open-circuit readings. Inspect the connector for green corrosion, bent pins, or a loose fit.

  3. 03

    Damaged thermistor wiring harness

    Part replacement

    The wire leads running from the thermistor to the PCB can become chafed, pinched, or rodent-damaged, causing an open or short in the circuit. Visually inspect the full wire run and perform a continuity check on each lead.

  4. 04

    Faulty PCB misreading a good signal

    Part replacement

    If the thermistor resistance tests correctly at both reference temperatures and the connector and wiring show no faults, the PCB's thermistor input circuit has failed internally. The board must be replaced in this case.

See the test procedure for each cause

Frequently asked questions about 45

What does 45 mean on a LG hvac?
Error code 45 means the outdoor unit's PCB is detecting an open or shorted circuit in the condenser coil thermistor, specifically the sensor located at the middle or exit (liquid line) position of the condenser coil. The board cannot get a valid temperature reading from that sensor. This will typically prevent normal operation to protect the system from running without accurate coil temperature data.
Can I fix error code 45 myself on a LG HVAC unit?
A knowledgeable DIYer can perform the initial diagnostic by disconnecting the thermistor, submerging it in water at a known temperature, and measuring resistance with a multimeter against the reference values of 2,800 ohms at 38°C and 10,000 ohms at 10°C. Replacing the thermistor is also a relatively straightforward repair. However, if the fault points to the PCB, replacement of that component involves working inside the outdoor unit's electrical panel, which is best handled by a certified HVAC technician.
Is error code 45 on a LG HVAC dangerous to ignore?
Running the system while ignoring this fault can lead to unmonitored condenser coil temperatures, which may allow the system to operate outside safe parameters. Over time this could cause refrigerant or compressor damage. It is advisable to diagnose and resolve the fault before continuing regular operation.
How much does it cost to repair error code 45 on a LG HVAC?
If the thermistor itself is the cause, parts typically cost in the range of $20 to $80 depending on the specific model, with labor adding $75 to $150 if a technician performs the work. If the PCB is at fault, board replacement is significantly more expensive, generally ranging from $200 to $600 or more for parts and labor combined.
Will resetting the LG HVAC unit clear error code 45?
A power reset may temporarily clear the error from the display, but the code will return as soon as the PCB polls the thermistor circuit and detects the same open or short condition again. Resetting does not address the underlying hardware fault. A proper repair of the thermistor, wiring, or PCB is required for the code to clear permanently.

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