All Four Rooms Went Warm: Single Leak At The Outdoor Unit
All four rooms lost cooling at the same time. When every zone drops together on a system 4, the fault almost certainly sits at the one component they all share. The question was what had failed and whether it could be repaired.
Case Details
| Unit | LGMulti-split |
|---|---|
| Age | 5 years old |
| Location | HDBSengkang, Singapore |
| Reported | The master bedroom lost cooling first, then the other rooms followed over the next few days. All four rooms were blowing warm. Initial assumption was that each room might have a different fault. The system was about five years old. |
Diagnostic Turning Point
- Concern: Worry was that each room had a separate fault, leading to multiple repair bills
- Previous advice: Homeowner thought one room had a separate fault because it lost cooling first
- Key check: Checking refrigerant pressure confirmed system-wide gas loss. Then bubble test at outdoor connections pinpointed the leak source
What We Checked
When all rooms lose cooling in close succession on a multi-split system, the outdoor unit is the common point. We checked the shared outdoor unit first before inspecting individual indoor units.
- 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. Full system replacement was approved.
The entire system was replaced. New outdoor unit and four 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.
Related Reading
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