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Error code reference

LG Hvac Error Code PF

PTAC Freeze Protection mode; indoor air thermistor shows PCB room temp less than 5°C/40°F.

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PTAC Freeze Protection mode; indoor air thermistor shows PCB room temp less than 5°C/40°F.

First step from the service manual

If room is not that temp, check air thermistor: must be 5,600Ω at 38°C/100°F & 20,700Ω at 10°C/50°F. Ohm thermistor in water, measure water temperature; 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 PF means on a LG hvac

The PF error code on an LG PTAC unit indicates that the system has entered Freeze Protection mode. This is triggered when the indoor air thermistor detects a PCB room temperature reading below 5°C (40°F). The PTAC unit activates this protective mode automatically to prevent damage to internal components and plumbing that could result from sustained freezing temperatures. It is not necessarily a fault in the traditional sense, but it does signal that something requires attention, whether that is actual cold conditions in the space or a malfunctioning thermistor sending an inaccurate reading to the control board.

The indoor air thermistor is a negative temperature coefficient (NTC) resistive sensor, meaning its resistance decreases as temperature rises. For this component to be functioning correctly, it must measure approximately 20,700 ohms at 10°C (50°F) and approximately 5,600 ohms at 38°C (100°F). If the thermistor has drifted out of spec, become contaminated, or developed a wiring fault, it can report a falsely low temperature to the PCB, triggering freeze protection even when the room is at a normal temperature. Verifying the thermistor involves submerging it in water of a known temperature and measuring resistance with a multimeter to compare against the expected values.

If the thermistor readings are accurate and the plug connection to the PCB is secure and clean, yet the PF code persists under normal room conditions, the PCB itself is likely misinterpreting the thermistor signal and should be replaced. Always rule out a genuinely cold room before condemning any components, as the system may be operating exactly as designed.

Source: manufacturer service documentation.

Common causes of PF

  1. 01

    Genuinely low ambient room temperature

    Wiring / connection

    If the room has actually dropped below 5°C (40°F), the unit is working as designed. Check the actual room temperature with a separate thermometer before diagnosing any components.

  2. 02

    Faulty indoor air thermistor

    Part replacement

    A thermistor that has drifted out of specification, corroded, or been damaged will send incorrect low-temperature readings to the PCB. Resistance should measure approximately 20,700 ohms at 10°C (50°F) and 5,600 ohms at 38°C (100°F); values outside this range confirm a failed sensor.

  3. 03

    Loose or corroded thermistor connector

    Wiring / connection

    A poor connection between the thermistor plug and the PCB can cause intermittent or incorrect resistance readings, mimicking a failed thermistor. Inspect the connector for corrosion, bent pins, or incomplete seating.

  4. 04

    Thermistor wiring damage

    Part replacement

    Damaged insulation, a pinched wire, or a broken conductor in the thermistor harness can alter the resistance signal reaching the board. Visually inspect the wiring run from the thermistor to the PCB for any visible damage.

  5. 05

    Failed PCB

    Part replacement

    If the thermistor tests within spec at the correct resistance values and the connector is properly seated, the PCB may be misinterpreting the signal. Board replacement is the appropriate next step after all other causes have been eliminated.

See the test procedure for each cause

Frequently asked questions about PF

What does PF mean on a LG hvac?
PF stands for Freeze Protection mode on an LG PTAC unit. It activates when the indoor air thermistor reports a PCB room temperature below 5°C (40°F). The code can indicate a genuinely cold space or a faulty thermistor sending an incorrect low-temperature reading to the control board. A technician should verify the actual room temperature and test the thermistor resistance before replacing any parts.
Can I fix the PF error code myself?
If the room is genuinely cold, heating the space and allowing the unit to return to normal operating temperature should clear the code. If the room is warm, diagnosing the issue requires a multimeter to test thermistor resistance at a known water temperature, which is a task many knowledgeable DIYers can perform. However, replacing the PCB if the thermistor checks out is a more involved repair that may be better suited to a qualified technician.
Is the PF error code on my LG PTAC a safety concern?
The PF code itself is a protective feature, not a hazard. It indicates the unit has detected potentially freezing conditions and has responded accordingly to protect internal components. That said, if the code is appearing because the room is genuinely that cold, there may be a broader concern about heating adequacy or building conditions that should be addressed promptly.
Will resetting the unit clear the PF error code?
A reset may temporarily clear the PF code, but if the underlying cause is a faulty thermistor or a failing PCB, the code will return once the unit re-evaluates the temperature signal. Resetting without addressing the root cause is not a long-term solution. The thermistor should be tested and the connector inspected before assuming a reset has resolved the issue.
How much does it cost to repair a LG PTAC showing a PF code?
Repair costs depend on which component is at fault. Thermistor replacement is generally the least expensive fix, typically ranging from a modest parts cost plus labor. PCB replacement is significantly more expensive, with parts alone often ranging from $150 to $400 or more depending on the model, plus labor time. Getting a diagnostic visit from a certified PTAC technician will provide a more accurate estimate for your specific unit.

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