Error Only After Hours of Running: Corroded Joint in Ceiling

An error arrives only after hours of running. What has to build up before a fault appears narrows the search considerably.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

How this presents

Errors coming and going on a system where the signal cable was extended at some point during its life. The join sits inside a ceiling void. Both units behave normally between the faults, which have grown steadily more frequent.

Setup: Mitsubishi Electric Wall-mounted10-12 yearsHDBYishun
Misread as: A board fault on one of the two units, needing an expensive part on a working system.
Check first: How many joins the signal run contains, and what encloses each one

What else produces this

The first useful question on a communication fault is how many joins the run contains. A spliced cable and a continuous one are very different propositions. A join is only as good as its enclosure and the environment around it, and a ceiling void stays warm and damp for most of the year. Locating the splices and opening them up is quicker than any electrical test, and it usually ends the search there.

Intermittent faults growing more frequent describe a connection degrading rather than a part failing.
A splice in the signal run identifies the one place the cable's continuity was broken.
An unsealed junction box in a damp void exposes that splice to conditions the cable itself resists.
Corrosion on the conductor faces inside the box explains a signal that has become unreliable.

Why it happens

Cable insulation keeps moisture off a conductor along the whole run except where it has been cut and joined. A splice inside an unsealed box has bare conductor surrounded by whatever air the void holds, and a ceiling void is warm and humid for most of the year. Corrosion builds on those faces steadily. The signal degrades gradually rather than stopping, which is why the faults get more frequent instead of arriving all at once.

What resolution involves

The splice is remade inside a properly sealed enclosure, or the run is replaced continuously where the route permits. A continuous run is the better answer wherever it is practical, because it removes the failure point rather than protecting it. Where a join genuinely cannot be avoided, sealing it properly is not optional in a ceiling void. Nothing else stands between exposed metal and wet air.

How to tell it worked

Every other join on the same installation opened and inspected at the same visit. Splices made together in the same conditions have aged together, whatever their current state looks like.

Before you approve a quote

Every join is a future fault waiting on the damp air

A continuous cable has no failure point along its length. Every splice adds one to the run.
Ask how many joins the run has and where they sit. A damp void is the worst place for one.
A sealed enclosure is all the protection a splice has. Unsealed, it is exposed metal in wet air.

Questions this case answers

Aircon error only appears after it has run for hours: why?

Because the failure is at a splice rather than in a part. The cable is protected along its whole run except where it was cut and joined. That splice sits in an unsealed box in a damp ceiling void, so corrosion builds on the bare conductor until the signal becomes unreliable.

Where do hidden wire joints usually sit in an older flat?

Inside a ceiling void, usually in a junction box added when the signal cable was extended. That position leaves the splice in warm, humid, still air, which is the worst place for it; both units behave normally between the faults while the join degrades.

Does an error that clears after a rest rule out a board fault?

Yes, in practice it does. A board fault does not usually come and go with running time, while an error that clears and returns points at a connection that is still touching. The joins in the run deserve inspection before any board is replaced.

Is it worth tracing the whole cable route before replacing a board?

Yes. The run was extended at some point and the join sits in a damp ceiling void, so find how many joins it has and what encloses each one. A splice that corroded means the others made in the same conditions are close behind it, and checking them costs far less than a board.

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