Jurong East block outdoor unit rocks: mounting bolt corroded and seized
A Jurong East flat had an outdoor unit that rocked visibly every time it started up, worse than a few months earlier. The estate mixes mature blocks with newer mall-adjacent developments nearby. A corroded, seized mounting bolt is easy to miss until the rocking actually becomes visible.
By Team Snowflake | Reviewed 11 Jul 2026
Case summary
York Wall-mounted10 years oldHDBJurong East, Singapore
- Concern
- The homeowner worried the compressor itself had a serious internal fault developing and would need a costly, full replacement.
- Found
- A corroded, seized mounting bolt let one corner of the unit shift slightly under vibration, rather than a fault developing inside the compressor itself
- Key check
- Checked each mounting bolt individually for corrosion and seizing before assuming an internal compressor fault
- Result
- Every startup since the corroded bolt was replaced has been rock-steady, with no further movement at any corner. Compressor work that would have cost far more than a bolt replacement was avoided entirely.
What we were told
The homeowner said the unit visibly rocked on its base for the first few seconds after every startup, then settled and ran normally. This had grown more noticeable over the past few months. It still cooled properly once it settled into steady running.
What we checked
The rocking's timing mattered most here: it showed up only in the first few seconds after startup, then vanished once the unit reached steady running. An internal compressor fault would normally affect performance throughout the run, not just that brief window. So before opening the compressor, we checked each mounting bolt individually for corrosion or play.
The compressor ran smoothly once settled, with no unusual internal noise during normal steady operation.
One of the four mounting bolts had corroded and seized, no longer holding that corner firmly in place.
The seized bolt let that corner of the unit shift slightly under load, unlike the other three corners.
The uneven base caused visible rocking specifically during the harder startup load each time it ran.
What we found
One of the four mounting bolts had corroded over time and seized in place. This likely came from years of moisture exposure at ground level building up gradually. With that bolt no longer holding its corner firmly, the unit could shift slightly under the harder mechanical load of startup. That shift was enough to rock the unit visibly on an otherwise stable base. It settled back down once running speed stabilised a few seconds later.
What fixed it
We replaced the corroded bolt and checked all four mounting bolts for the same corrosion risk, so every corner sits tight and even. We did not recommend any compressor work, since it tested normally once isolated from the mount. We advised checking all four mounting bolts at every future service, not just the one that visibly seized this time.
Outcome
Every startup since the corroded bolt was replaced has been rock-steady, with no further movement at any corner. Compressor work that would have cost far more than a bolt replacement was avoided entirely.
What this case teaches us
Visible rocking on startup often means a corroded bolt, not the compressor
- A unit that visibly rocks on startup, rather than just sounding louder, often points at a corroded, seized mounting bolt.
- A single seized bolt can make a corner shift and a compressor look unstable even when it's working fine.
- Ask for every mounting bolt to be checked individually for corrosion before approving compressor replacement.
Related reading
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