If your LG Multi V system is showing error 35 — or CH35, or 351/352/353 — low side pressure dropped far enough that the system stopped itself.
Refrigerant is the usual answer. But it is not the only one, and that distinction is worth several thousand dollars.
What this means for your building
The outdoor unit monitors pressure on the low side of the refrigerant circuit. Error 35 is raised when that pressure falls excessively and stays there — the system shuts down rather than run the compressor in conditions that damage it.
The manual defines the triggers precisely, and they differ by operating mode:
| Mode | Trigger |
|---|---|
| Cooling | Low side below roughly 400 kPa (58 psi) for one minute, high side under about 2,200 kPa (319 psi) |
| Heating | Low side below roughly 230 kPa (33 psi) for one minute |
There is also a low-load condition: a shutdown when combined compressor frequency is under 30 Hz and pressure sits below roughly 110 kPa (16 psi) for a minute.
The detail most people miss
Here is the genuinely useful part, and it is in the manual rather than in any code list published online.
The mode you are running in points at a different component.
- In cooling, the manual directs you toward a refrigerant leak or a defective indoor unit expansion valve
- In heating, toward a leak or a defective outdoor unit expansion valve
So if your system throws CH35 only in cooling, that is a meaningful clue. It narrows the search from “somewhere in the building” to a specific class of component. Telling us which mode it appears in genuinely shortens the first visit.
Leak, or valve?
This is the question that decides your cost, and it should be answered before anyone connects a refrigerant hose.
If it is a leak, you need leak detection, repair, recovery, pressure testing, evacuation and recharge. On a commercial VRF system with a large charge across long pipe runs, that is a substantial job.
If it is an expansion valve, you need a component replaced and the charge is fine.
Both produce low pressure. Both look similar on gauges. Adding refrigerant to a system whose valve has failed does not fix anything — and it can overcharge the system, creating a high pressure fault on top of the one you started with.
The sub-codes
| Sub-code | Unit |
|---|---|
| 351 | Master outdoor unit |
| 352 | Slave outdoor unit 1 |
| 353 | Slave outdoor unit 2 |
On multi-module systems this identifies which unit to attend immediately.
How urgent is it?
Urgent, and the urgency is financial if it is a leak.
Refrigerant escaping is escaping now, and the amount lost drives what the recharge costs. There is no version of waiting that makes this cheaper.
There is equipment risk either way. Refrigerant carries oil around the circuit and helps cool the compressor. Whether the shortfall comes from a leak or a restriction, the compressor is running hot and under-lubricated for as long as the condition persists.
What causes it
- Refrigerant leak — the most common, and the expensive one
- Failed or stuck expansion valve — indoor unit in cooling, outdoor unit in heating
- Restriction in the pipework or a blocked filter
- Faulty low side pressure transducer reporting a drop that is not real
- Undercharge from previous work where the system was never correctly filled
- Genuine low load conditions combined with a marginal fault
What happens if you leave it
If it is a leak, two things compound. The leak grows, so the eventual recharge costs more. And the compressor runs undercharged in the meantime, which is one of the standard routes to the most expensive repair on the system.
If it is a valve, the affected circuit cannot deliver properly and the compressor still runs in conditions it was not designed for.
Either way, the component absorbing the consequences is the one you least want to replace.
What we check
- Use the sub-code to identify which outdoor unit reported the fault.
- Note which mode it occurs in — cooling and heating point at different valves.
- Verify the pressure transducer before assuming anything about charge.
- Measure system pressures against the documented thresholds.
- Test expansion valve operation — this comes early, not after a recharge.
- Assess refrigerant charge against design.
- Leak detection if the charge is genuinely low, with pressure testing to prove any repair.
- Review service history — prior top-ups almost always mean an unrepaired leak.
What you can tell us before we arrive
- Has refrigerant been added before? The single most useful thing you can tell us.
- Does it happen in cooling, heating, or both? This narrows the component materially.
- The sub-code — 351, 352 or 353 identifies the module.
- When did capacity start dropping? Performance usually declines before the code appears.
Related codes
- 42 — Low pressure sensor error. The sensor itself faulty rather than a real pressure condition.
- 150 — Liquid flood-back warning. The opposite end of the same measurement problem.
- 204 — Heat recovery unit communication. Routing problems can affect where refrigerant ends up.
Find the cause before adding refrigerant
We are certified on LG, Daikin and Mitsubishi VRF platforms, and we service systems we did not install — including systems somebody else has been topping up.
Next business day service for commercial VRF.
Related codes
Error 42 is a low pressure sensor fault — the sensor itself, disconnected or shorted, rather than an actual pressure problem in the system.
Error 150 warns that liquid refrigerant is at risk of flooding back to the compressor. It is a protective warning before damage, not after it.
Error 204 means the outdoor unit is receiving no signal from the heat recovery unit — the box that lets one zone heat while another cools.
Frequently asked questions
What does error code 35 mean on an LG Multi V system?
The outdoor unit low side pressure transducer detected an excessive drop in pressure and the system shut down. On commercial Multi V the most common underlying cause is a refrigerant leak, though a failed expansion valve produces a very similar reading.
Does CH35 always mean a refrigerant leak?
Not always, and the distinction matters financially. The manual names a defective expansion valve alongside low charge as a cause. A valve replacement is a moderate repair; a leak on a commercial system is considerably more involved and expensive.
Why does the mode I am running in matter for error 35?
Because it points at a different valve. In cooling the manual directs you toward a faulty indoor unit expansion valve, and in heating toward an outdoor unit valve. Telling us which mode the fault appears in genuinely narrows the search.
What do sub-codes 351, 352 and 353 mean?
They identify which outdoor unit raised the fault. 351 is the master, 352 is slave one and 353 is slave two. On a multi-module installation that tells us which unit to attend rather than checking every module in turn.
Should I add refrigerant to clear a CH35?
Not before the cause is established. If the problem is a restriction or a failed valve rather than a shortage, adding refrigerant does not fix it and can overcharge the system, which creates a high pressure problem on top of the original fault.
How much does an error 35 cost to resolve?
It depends entirely on the cause. A faulty pressure transducer is modest and an expansion valve is a moderate component repair. A confirmed leak on a commercial VRF system is the expensive end, because of charge volume and the work to locate and prove the repair.