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Error code reference

LG Hvac Error Code 35

Low pressure switch opened, under 14 PSI.

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Low pressure switch opened, under 14 PSI.

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What 35 means on a LG hvac

Error code 35 on an LG HVAC system indicates that the low pressure switch has opened, meaning refrigerant pressure in the low-pressure side of the refrigerant circuit has dropped below 14 PSI. The low pressure switch is a safety device that monitors suction-side pressure. When pressure falls below the set threshold, the switch opens and signals the control board to halt compressor operation, preventing damage that could result from running the compressor under a refrigerant-starved condition.

The most common underlying cause of this fault is a refrigerant leak somewhere in the system. As refrigerant escapes, suction pressure drops progressively until it crosses the 14 PSI threshold and triggers the switch. Other causes include a severely restricted or blocked expansion valve or metering device, which starves the evaporator of refrigerant and causes suction pressure to collapse. Extremely low ambient temperatures can also cause low suction pressure by reducing the rate of refrigerant evaporation.

Diagnosing this code requires connecting a refrigerant manifold gauge set to confirm actual system pressures. If suction pressure is indeed at or below 14 PSI, the technician must determine whether the cause is refrigerant loss, a restriction in the metering device, a failed TXV, airflow problems across the evaporator, or a faulty low pressure switch itself providing a false reading. Refrigerant handling requires EPA Section 608 certification.

Source: manufacturer service documentation.

Common causes of 35

  1. 01

    Refrigerant leak

    Part replacement

    A leak in the refrigerant circuit causes suction pressure to drop below 14 PSI over time. Signs include ice on the refrigerant lines, reduced cooling performance, or oily residue near fittings and connections.

  2. 02

    Restricted or failed metering device (TXV or orifice)

    Part replacement

    A clogged or failed thermostatic expansion valve or fixed orifice restricts refrigerant flow into the evaporator, causing suction pressure to collapse. This can mimic a low-charge condition on the gauges.

  3. 03

    Blocked or dirty evaporator coil

    Wiring / connection

    Heavy dirt or ice buildup on the evaporator coil severely reduces heat absorption, lowering evaporator pressure below the switch threshold. Inspect the coil for blockage and check that airflow across it is unobstructed.

  4. 04

    Very low ambient operating temperature

    Wiring / connection

    Operating the system in ambient temperatures far below its rated range reduces refrigerant evaporation rates and suction pressure. Check the unit's minimum operating temperature specification and verify outdoor conditions at the time of fault.

  5. 05

    Faulty low pressure switch

    Part replacement

    The switch itself can fail and open at pressures above 14 PSI, producing a false error code 35. Verify actual system pressure with a gauge set before condemning the switch.

See the test procedure for each cause

Frequently asked questions about 35

What does 35 mean on a LG hvac?
Error code 35 on an LG HVAC unit means the low pressure switch has opened because refrigerant pressure on the suction side of the system dropped below 14 PSI. The system shuts down the compressor automatically to prevent internal damage. This is a protective fault that requires diagnosis of the refrigerant circuit before normal operation can resume.
Can I fix error code 35 on my LG HVAC myself?
Some causes, like a dirty evaporator coil or blocked air filter, can be addressed without professional help. However, if the root cause is a refrigerant leak or a failed metering device, those repairs require EPA Section 608 certification to legally handle refrigerants and should be performed by a licensed HVAC technician. Attempting to add refrigerant without locating and repairing a leak is a temporary fix at best and illegal to vent refrigerant to the atmosphere.
Is it safe to keep running my LG HVAC when error code 35 appears?
No. The system will not run the compressor while the fault is active, and you should not attempt to bypass or override the low pressure switch. Running a compressor with insufficient refrigerant pressure can cause overheating of compressor windings, oil starvation, and permanent compressor failure. Leave the system off until the underlying cause is diagnosed and corrected.
How much does it cost to repair error code 35 on an LG HVAC?
Repair costs depend heavily on the root cause. A coil cleaning or filter replacement may cost between $75 and $200 in labor. If the system needs refrigerant and a leak repair, costs typically range from $200 to $800 or more depending on the refrigerant type, leak location, and labor involved. A failed TXV or low pressure switch replacement can add $150 to $400 in parts and labor. Always get a diagnosis before committing to repairs.
Will resetting my LG HVAC clear error code 35?
Resetting the unit by cycling power may temporarily clear the fault and allow the compressor to restart, but if the underlying low pressure condition still exists, the switch will open again and the error code will return quickly. A reset does not fix the cause of the low pressure. A proper diagnosis with refrigerant manifold gauges is necessary to resolve the fault permanently.

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