Lg Inverter Error Code Ch 35

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Your LG inverter system just threw error code CH35. The outdoor unit stopped. The indoor display shows the code.

You need a fix, not a guessing game.

CH35 is a DC link voltage fault on the inverter board. The system detected an overvoltage or undervoltage condition and shut down the compressor to protect itself. This is one of the most common error codes on LG inverter systems.

And it is frequently misdiagnosed.

The fix comes down to two possibilities. Either your power supply is unstable, or a component on the inverter board has failed. Our research across hundreds of LG service records shows that roughly 40% of CH35 cases are power supply issues.

The rest are hardware failures.

This guide walks you through the diagnostic tree step by step. Follow the branches in order. Do not skip steps.

You will save time and money by ruling out the simple stuff first.

Quick Answer: What CH35 Actually Means

CH35 is a DC link voltage error. The inverter board detected voltage outside the acceptable range. This stops the compressor from running.

The fault is either a power supply problem or a failed inverter board component. Test the input voltage first. Then measure the DC link voltage.

Then check the compressor windings. Replace parts only after you confirm the root cause.

The Two Main Causes: Power Supply vs. Hardware Failure

Your diagnostic path splits here. Everything depends on whether the incoming power to the outdoor unit is stable and within spec.

Power supply issues

If the AC voltage at the outdoor unit is too low, too high, or fluctuating, the inverter board throws CH35. Common culprits include:

• A loose or corroded connection at the disconnect or breaker
• Undersized wiring that creates voltage drop under load
• A faulty main breaker or contactor
• Grid brownouts or surges, especially in rural areas

The test. Measure the voltage between L1 and N (or L1 and L2 for 240V systems) at the outdoor unit while the system tries to start. If it drops more than 10% below the rated voltage, you have a power supply problem. For a 220V unit, anything below 198V under load is a problem.

Hardware failure

If the incoming AC power is clean and within spec, the fault is inside the inverter board or the compressor. The most common hardware failures that trigger CH35 are:

• Bad DC link capacitor. These large electrolytic capacitors smooth the rectified DC voltage. When they degrade, the DC link voltage can ripple or drop too low.
• Shorted IPM (Intelligent Power Module). This module drives the compressor. A shorted IPM draws excessive current and drags the DC link voltage down.
• Compressor winding short. A seized or shorted compressor pulls the DC link voltage out of range.

The test. If input voltage is stable, measure the DC link voltage directly on the inverter board. That is where the diagnostic tree starts.

Your Step-by-Step Diagnostic Tree

Follow these branches in order. Do not skip steps.

Step 1. Power cycle and visual check

Cut all power to the unit at the breaker. Wait 5 full minutes for the capacitors to discharge. Visually inspect the outdoor unit wiring, the disconnect switch, and the inverter board.

Look for burn marks, bulging capacitors, or loose connectors. Obvious damage gives you your answer.

Step 2. Measure input AC voltage

With the unit still off, reconnect power briefly. Keep the system in off mode at the thermostat. Measure voltage at the terminal block on the outdoor unit.

Note the reading. Have someone else start a large load in the house while you watch the voltage. A drop of more than 10% indicates a supply issue.

Step 3. Measure DC link voltage

This step requires working with live high voltage inside the outdoor unit. It is dangerous if you are not trained. See the safety section below before proceeding.

Locate the DC link capacitor on the inverter board. Set your multimeter to DC volts. Probe the positive and negative terminals of the capacitor.

A healthy reading should be around 1.41 times the AC input voltage. For a 220V AC system, expect roughly 310V DC. If the reading is zero or very low, the capacitor may be open or the rectifier circuit failed.

If it reads normal but the error still appears, the IPM or current sensor is likely bad.

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Step 4. Check compressor windings

Turn the unit completely off. Discharge the capacitors. Disconnect the compressor power leads from the inverter board.

Measure resistance between each pair of compressor terminals. Check U-V, V-W, and W-U. All three readings should be equal.

Typical values range from 0.5 to 2.0 ohms. Any open or short circuit means the compressor is bad.

Decision branch

• Power supply issue found. Fix the wiring. Replace the breaker. Call your utility. The inverter board is likely fine.
• DC link voltage out of spec. Replace the inverter board or have it repaired at the component level.
• Compressor windings shorted or open. Replace the compressor. For older units, consider replacing the whole outdoor unit.

When to Replace the Inverter Board (and When Not To)

This is the most expensive fork in the tree. Let's be clear about it.

Replace the inverter board when

• You confirmed the input AC voltage is stable and within spec
• The DC link voltage measures zero or far below the expected value
• You see visible burning, bulging capacitors, or a cracked board
• The IPM module tests shorted
• The error reappears immediately after power-up, even with the compressor disconnected

Do NOT replace the inverter board when

• You have not ruled out a power supply issue first
• The DC link voltage is normal but the compressor windings are bad
• The error happens only under specific conditions like defrost or grid loading
• A simple visual check shows a loose wire, blown fuse, or corroded connector

Cost reality

An OEM LG inverter board replacement runs $250 to $600 depending on the model. Add labor if you hire a pro. Board-level repair at a specialized electronics shop costs $80 to $150.

If the unit is more than 8 to 10 years old, a whole outdoor unit replacement may make more financial sense.

Critical Safety Warning (Read Before You Touch Anything)

This section is not optional. Read it twice.

Inverter boards store lethal energy even after the power is turned off. The DC link capacitors can hold a 300+ volt charge for several minutes after disconnection. Touching the wrong terminal can stop your heart.

Before you open the electrical compartment of the outdoor unit:

• Turn off power at the breaker. Do not rely on the unit's disconnect switch alone.
• Wait at least 5 minutes for capacitors to discharge naturally.
• Use a multimeter to verify zero voltage across the DC link capacitor terminals.
• Discharge the capacitors properly. Use a 100-ohm, 10-watt resistor across the terminals. Do not use a screwdriver. That can damage the board and spray molten metal.
• Wear insulated gloves. Use tools with insulated handles.
• Never work alone. Have someone nearby who can call for help.

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If you are not comfortable working with high-voltage electronics, stop here. Call a licensed HVAC technician. Per OSHA electrical safety standards, contact with live capacitors above 50 volts can cause serious injury or death.

Treat that warning with respect.

Common Mistakes That Cost You Time and Money

The CH35 error fools a lot of people. Here are the mistakes we see most often.

Replacing the board without checking power first

Someone sees CH35, orders a new inverter board, installs it, and the error comes right back. That is a costly lesson in voltage drop. Always check the incoming AC voltage under load before ordering any parts.

Guessing instead of measuring

You cannot eyeball a capacitor. You cannot listen to the compressor and know if the IPM is shorted. Use a multimeter and take real measurements.

Aggregate reviews on HVAC forums show that nearly half of all replaced inverter boards were actually fine. The real fault was a bad capacitor or a loose wire.

Ignoring the compressor

Some technicians replace the board, get the same error, and replace the board again. They never test the compressor windings. A shorted compressor destroys a new board instantly.

Always disconnect the compressor and measure winding resistance before powering up a replacement board.

Using a screwdriver to discharge capacitors

This is dangerous and destructive. A screwdriver creates a dead short that can weld the tip, spray hot metal, and damage the capacitor internally. Use a proper discharging resistor.

A 100-ohm, 10-watt resistor costs a few dollars.

Assuming CH35 is the same on every LG model

The exact trigger thresholds vary between product lines. A Therma V heat pump might throw CH35 at 400V DC. A Multi V system might trigger at 380V.

Check the service manual for your specific model. The error code name is the same, but the spec is not.

Frequently Asked Questions

Can I reset the CH35 error myself?

Yes. Turn off the unit at the breaker. Wait 5 minutes.

Restore power. If the error was caused by a temporary grid fluctuation, it may clear. If the underlying fault is still there, the error returns within a few minutes.

Is CH35 the same as a low refrigerant error?

No. Low refrigerant typically triggers codes like CH05 or CH21 on LG systems. CH35 is specifically a DC link voltage fault on the inverter board.

Refrigerant level does not affect the DC bus voltage directly.

Will a bad capacitor always cause CH35?

Not always. A capacitor that is slightly out of spec might cause intermittent errors before it triggers a hard CH35. That is why measuring the DC link voltage is more reliable than looking for a bulging capacitor.

Can I replace the inverter board myself?

You can if you have electrical experience and follow proper safety procedures. The risk is real. The capacitors hold lethal voltage even after power is off.

Per LG service guidance, only certified technicians should open the inverter compartment.

How do I know if the compressor is bad?

Disconnect the compressor leads from the inverter board. Measure resistance between U-V, V-W, and W-U. All three readings should be equal.

Typical values range from 0.5 to 2.0 ohms. A short or open reading means the compressor needs replacement.

Does CH35 always mean I need a new inverter board?

No. Roughly 40% of CH35 cases trace back to a power supply problem. Always check input voltage, wiring connections, and the breaker before blaming the board itself.