Why did all rooms stop cooling at the same time?

A system 4 connects all indoor units to a single outdoor unit on one refrigerant circuit. When the outdoor unit leaks gas, pressure drops across the whole system, affecting every room.

Can you repair the outdoor unit on a system 4 without replacing indoor units?

It depends on the extent of corrosion and the condition of the indoor units. If the indoor units are still in good shape, outdoor-only replacement is possible. In this case, the indoor units had also accumulated enough wear to justify a full change.

Why did one room lose cooling before the others?

Rooms with longer pipe runs feel the pressure drop first because refrigerant has further to travel. As the leak continues, the remaining rooms follow.

LG System 4 Gas Leak at Outdoor Unit Affecting All Rooms

Aircon case in Sengkang, Singapore: cooling loss traced to gas leak at outdoor unit pipe connections on shared system 4 outdoor unit, causing cooling loss across all rooms after targeted diagnosis checks.

Case Details

Reported: The master bedroom lost cooling first, then the other rooms followed over the next few days. Now none of the rooms are cold. I thought each room might have a different problem. The system is about five years old.
Unit: LG · Multi-split · 5 years old
Location: HDB · Sengkang, Singapore

What We Checked

Refrigerant pressure was very low across the entire system.
All four indoor units were blowing air but not cold — consistent with system-wide gas loss.
Outdoor unit pipe connection manifold showed corrosion and oxidation on multiple joints.
Bubble test confirmed active leaks at two connection points on the outdoor unit.
LG error code CH35 was active on the system controller.

The Diagnosis

The shared outdoor unit had developed gas leaks at the pipe connection manifold where all four indoor unit lines connect. Corrosion had spread across multiple joints. Because a system 4 runs all indoor units on a single refrigerant circuit through one outdoor unit, the gas loss affected cooling in every room simultaneously. The master bedroom lost cooling first because its indoor unit has the longest pipe run, making it the first to feel reduced pressure.

What Fixed It

We explained that welding multiple corroded joints on a system 4 manifold carries significant risk — if one repair fails, the entire system loses cooling again. With corrosion on multiple connection points and the indoor units also showing age-related wear, we recommended full system replacement. We walked through the option of outdoor-only replacement, but the indoor units had accumulated enough wear that a full change made more sense for long-term reliability. The homeowner agreed to replace the full system.

The entire system was replaced — new outdoor unit and four new indoor units installed, piping pressure-tested, and refrigerant charged to specification. Cooling returned across all rooms with no further gas loss.

Why This Happens

How a single outdoor unit leak affects all rooms in a system 4.

A system 4 connects four indoor units to one outdoor unit. All share the same refrigerant circuit.
When the outdoor unit develops a gas leak, refrigerant drops across the entire system — not just one room.
If all rooms lose cooling around the same time, the outdoor unit is almost always the source.
Partial repairs are less viable on system 4 outdoor units because the corrosion pattern affects the shared connection manifold.

Same situation with your aircon?

Describe what’s happening. We’ll work out the likely cause and tell you the right next step.

WhatsApp us