LG Aircon CH35 CH38 Gas Leak

The most common leak point on LG outdoor units is at the pipe connections — the flare joints where copper refrigerant lines meet the service valves. These joints rely on a precise metal-to-metal seal under high pressure. Any gap, scratch, or corrosion on the sealing surface creates a path for refrigerant to escape.

On some LG models, the connection layout positions these joints where moisture pools around them. In Singapore, where outdoor units face constant humidity, rain splash, and salt exposure near the coast, corrosion at those joints accelerates. Green or white oxidation around the pipe fittings is a visible sign that the sealing surfaces are degrading.

The second common leak source is inside the outdoor unit at brazed joints — the U-bends and return bends in the condenser coil. These joints are stressed by thermal expansion every time the system cycles on and off. Over thousands of operating hours, the copper fatigues where it meets the braze alloy, and a crack opens. This type of leak is harder to detect because the crack may only open under operating pressure, not when the system is off.

A third source — less visible but increasingly common on units near the coast — is pitting corrosion on condenser coil tubes. Salt particles and aggressive cleaning chemicals strip the protective oxide layer from copper and aluminium surfaces. Pinholes develop slowly and produce a leak rate that can take months to become noticeable. By the time the homeowner notices weak cooling, a significant portion of the refrigerant charge may already be gone.

A detail that matters for diagnosis: slow leaks and sudden leaks behave very differently. A slow corrosion leak drains the system over weeks or months. Cooling fades gradually, and homeowners often adapt without realising the decline. A fatigue crack at a brazed joint can open more abruptly — cooling drops noticeably within days, and oil stains may appear near the outdoor unit. The speed of the decline tells the technician where to look first.

Singapore's outdoor environment is unusually hostile to refrigerant connections. Year-round humidity above eighty percent accelerates oxidation on copper tubing and creates the moisture needed for formicary corrosion — a type of subsurface attack that tunnels through copper from the inside. It starts with organic acids from household cleaning products, paint fumes, or renovation materials reacting with moisture on the copper surface. The tunnels are invisible until a pinhole finally breaks through from the inside out.

Modern refrigerants add mechanical stress that older systems never faced. R410A operates at roughly sixty percent higher pressure than the R22 it replaced. R32, now common in newer LG units, runs at similar pressures but with a smaller molecular weight — meaning it can escape faster through the same size opening. Every connection, every braze point, and every flare joint is under significantly more stress than equivalent joints on older systems. This is one reason why leak patterns show up sooner on newer units than homeowners expect.

Units on higher floors face additional wind-driven rain that hammers exposed joints. Coastal areas — East Coast, Pasir Ris, Sentosa — add salt particles that cling to condenser coils and copper fittings, causing galvanic corrosion where copper tubes contact aluminium fins. The two different metals in the presence of saltwater create an electrochemical reaction that eats through the copper faster than simple oxidation alone.

Unlike temperate climates where systems get seasonal rest, Singapore aircon runs heavily year-round — often eight or more hours daily. Every cooling cycle expands and contracts the copper lines. This constant thermal cycling fatigues brazed joints faster than in countries where systems shut down for months at a time. The compressor vibration compounds the effect, transmitting high-frequency stress through every connected pipe run.

Mounting also plays a role. Outdoor units that sit on metal brackets without proper vibration dampening pads transmit compressor vibration directly through the mounting points and into the connected pipework. Over time the rubber isolators that absorb this vibration degrade — especially in tropical heat — and the amplitude reaching the pipe joints increases. Units mounted on narrow HDB aircon ledges with minimal clearance are particularly exposed because maintenance access is limited and the isolators rarely get inspected.

Refrigerant does not deplete naturally. A sealed system should hold its charge for the entire lifespan of the unit — often a decade or more. If a technician tops up gas and the cooling fades again within weeks, there is an active leak. The top-up only masks it temporarily while the gas escapes through the same unfixed opening.

Each cycle of low refrigerant causes compounding damage that is not immediately visible. Refrigerant doubles as the compressor lubricant — it carries oil through the system to keep internal bearings and seals from overheating. When the charge drops, oil circulation drops with it. The compressor runs hotter, bearings wear faster, and winding insulation degrades. This damage accumulates silently across every top-up cycle. The compressor may test fine today but fail months later from the cumulative stress.

The pattern is predictable. The first top-up might hold if the issue was a slight undercharge from installation. When cooling fades again within weeks, the second top-up confirms an active leak somewhere in the system. By the third top-up, the compressor has endured multiple rounds of running on insufficient lubrication. At that point, the risk of compressor failure is real — and replacing a compressor costs far more than the leak repair would have on the first visit.

The correct sequence is always: trace the leak first, repair it, then recharge to the manufacturer specification. A technician who tops up gas without performing leak detection — using an electronic sniffer, UV dye, or nitrogen pressure hold test — is treating the symptom rather than the cause.

A single corroded flare connection on otherwise healthy copper can be brazed and resealed. This is the simplest fix — the joint is accessible, the repair is testable with a nitrogen pressure hold, and the cost is a fraction of replacement. If the surrounding pipe shows no spread of corrosion and the system is relatively new, brazing is a reasonable path. The repaired joint gets a filter drier replacement and a full recharge to factory specification.

When corrosion has spread along the pipe surface or multiple joints show degradation, brazing one spot often leads to a new leak nearby within months. The underlying corrosion is systemic — fixing one location does not prevent the next weak point from opening. At that point, replacing the affected pipework or the outdoor unit as a whole is more durable than chasing leaks one by one.

If the compressor has already sustained damage from running on low refrigerant — confirmed by abnormal amp draw, elevated winding resistance, or excessive discharge temperatures — the outdoor unit needs replacement regardless of where the leak is. Fixing the leak on a damaged compressor delays the failure but does not prevent it. The internal wear from running dry is not reversible.

The economic threshold is straightforward. When the sum of recent repairs plus the projected cost of the next likely repair approaches half the cost of a new system, replacement is the financially sound path. This applies especially to systems older than seven or eight years where the outdoor unit has been exposed to Singapore weather for its entire life. For systems still on R22 refrigerant — now phased out and increasingly expensive to source — the cost calculation tilts even further toward replacement with a modern R32 unit.

CH35 on an LG system means the low-side refrigerant pressure has dropped below the safe operating range — typically below fifteen PSI. The system flags this to protect the compressor from running dry. It confirms a significant refrigerant loss, not a marginal shortfall. A system showing CH35 has lost enough gas that the compressor is no longer receiving adequate cooling and lubrication.

CH38 triggers when the refrigerant charge falls below the minimum threshold — roughly forty percent of the factory charge. At this point the system locks out entirely and will not restart until the fault is cleared. This is the most protective code in the LG refrigerant monitoring sequence. By the time it appears, the compressor has been running on insufficient refrigerant for some time.

When either code appears, do not reset and restart repeatedly. Each restart attempt on low refrigerant forces the compressor to start against abnormal pressures with inadequate lubrication. The right sequence is a full leak trace, nitrogen pressure test, and compressor health check — measuring amp draw and winding resistance — before deciding between repair and replacement. If the compressor tests healthy and the leak source is accessible and repairable, a proper fix is still viable. If the compressor shows elevated readings, the outdoor unit needs to be replaced regardless of the leak location.

Other LG codes that relate to refrigerant issues include CH24, which flags abnormal refrigerant pressure without specifying direction, and CH32, which indicates excessively high discharge temperature — often a secondary symptom of low gas causing the compressor to overheat. If you see any combination of these codes, the refrigerant circuit needs a full assessment before the system runs again.