is it safe to leave air conditioner on when not home

Generally, yes—it’s safe, but it’s also a spectacular way to feed your power bill.

Modern split-systems are designed to run unattended if they’re properly installed and regularly serviced; clean filters and a clear outdoor unit are non-negotiable.

If you want the house tolerable at knock-off, use a timer or smart control and set cooling to 24–26°C (or heating to 18–20°C), not arctic/sauna extremes.

Exceptions: keeping pets safe in heatwaves or managing humidity in the tropics—fair enough, but still schedule it.

Long story short: safe, yes; smart, only if you’re deliberate about it.