I am not sure if this question fits here. But it's important and it's about troubleshooting and electric problem. So I will try...

My air conditioner shows from time to time electric sparks for the past two days. Today the air con electrician came and he put a new cable between the unit inside the room and the compressor outside. And we tested it for about 30min and all looked fine. But now the sparks are back again. Where should we look for the problem?

Here are some details: This is happening in a high rise building in Bangkok with tropical climate. Currently it's about 30 degrees Celsius and 80% humidity. The air-con is maybe 5 years old, it's the traditional type, no modern converter version.

The sparks, if they show at all, are 90% of the time on one side of the Evaporator (the unit in the room where the cold air comes outside). On that side the yellow/green earth wire is connected to the metal of the unit. The sparks are sometime only small, I hear a short "tick" noise and see almost nothing. But sometimes the tick noise is loud and the spark is clearly visible from a distance.

But sometimes the sparks happen somewhere else. I saw sparks also twice in the ceiling near, or maybe in, a metal distribution box.

The problem happened the first time two days ago. We saw the sparks sometimes every few seconds and sometimes only once in half an hour. Obviously I switch the air-con off if it happens. But then we tried again, maybe an hour later. Then there are maybe no sparks for 20 minutes, and then they start again.

It seems the sparks only happen if the compressor outside is actually running. If I use the unit only to blow the fan, without the compressor running, then I don't see the sparks.

Normally I hear a humming noise from the compressor outside when it's running. When the sparks happen then that humming noise is temporarily (maybe for a second) less, like someone pulled the plug and put it in again after a second.

Like I wrote above, the air-con technician was here and he inspected the unit in the room and found no blank cables or something similar. So he decided to replace two cables which run in the ceiling from the indoor unit to the compressor. One cable has 3 power wires (plus, minus, earth) and one is the control cable with 2 wires.

When he finished the job all looked fine. He left maybe 30 minutes later while the air-con and compressor were running. After maybe 30 minutes more the sparks started again.

The breaker (fuse) did not switch off with all these sparks.

We have to keep in mind this is a Thailand electrical installation. Here electricians don't always follow the rules they should follow - if they know the rules at all.

There is also a problem that we have mice in the building recently. Maybe one of those creatures ate through the insulation somewhere?

**Where to look for the problem?**

Now I ask this question here because I am sure when the technician arrives tomorrow he will think about where else the problem could be. He replaced one cable and that was probably not the problem. So what else should he check or test or replace?

The air-con guy has worked at his job for many years. But I am pretty sure he didn't go to university and study electrical engineering. He likely won't analyze the situation too carefully...

Any ideas where to look for what kind of problems are welcome. We have to keep in mind that sometimes it works just fine for 30 minutes. So finding the problem is not easy. And even if we think it's fixed we won't know until hours later...