Breaker tripping with a hot smell: damaged isolator, not compressor
The breaker kept tripping and a hot electrical smell hung around the outdoor unit. Earlier advice was that the compressor had gone. But the smell came from one spot, and that spot was not the compressor.
By Team Snowflake | Reviewed 26 Feb 2026
Case summary
LG Wall-mounted12 years oldHDBToa Payoh, Singapore
- Concern
- The risk looked like an internal compressor short, which would mean a full and costly replacement.
- Found
- Heat-damaged isolator connection caused intermittent trips and smell
- Key check
- Checked isolator and wire connection heat marks before condemning the compressor
- Result
- Trips stopped, the hot smell did not return, and full cooling resumed with the original compressor still in service.
What we were told
The breaker had been tripping on and off for about a week. A hot electrical smell hung near the outdoor unit. The owner had switched everything off to be safe. Earlier advice was that the compressor had likely shorted.
What we checked
A trip with a localised smell calls for the power path to be checked before the compressor is opened. We started at the isolator and worked inward along the cable run. The trip pattern was the first clue. A compressor short trips the breaker instantly on every start. This unit tripped intermittently under load, which points to a loose connection that heats up until the breaker cuts out. We followed the smell to the isolator box and opened it.
Trips were intermittent under load, not instant on every start attempt.
Isolator wire connection showed visible heat discolouration and pitting on the contact surface.
Hot smell concentrated at the isolator box, not at the compressor housing.
What we found
One isolator wire connection had worked loose over twelve years. The metal expands a little each time the unit heats under load and shrinks again when it stops, and over the years that slowly slackened the connection. A loose connection carries power poorly, and under compressor load it heats up. The hotter it ran, the worse the contact became, which is why the trips grew more frequent through the week and why the breaker held when the unit sat idle. The smell stayed at the isolator box because that was the only spot generating heat. That single hot point, away from the compressor, confirmed the fault was electrical and minor. The compressor, wiring, and breaker were all working correctly.
What fixed it
We explained the findings and recommended replacing the heat-damaged isolator wire connection and cleaning every contact surface in the switch assembly. The old connection was too pitted and deformed to tighten reliably. Simply re-tightening a damaged contact buys a few months before it loosens again. After fitting a new wire connection and tightening every connection in the isolator box, we ran the unit under full compressor load for thirty minutes. The breaker held steady with no trips and no temperature rise.
Outcome
Trips stopped, the hot smell did not return, and full cooling resumed with the original compressor still in service.
What this case teaches us
How the breaker trips tells you where the fault is
- A compressor short trips the breaker the instant power is applied, every time. This unit tripped intermittently under load, which points to a loose connection, not a dead compressor.
- A hot electrical smell has a source. Following it to the isolator box, not the compressor, found the fault before any major part was condemned.
- Note when the trips happen and whether they are getting worse. That pattern is what guides the first test.
Related reading
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