Fujitsu split intemittantly turns off.

Hi all,
My Mum's Fujitsu AOT24RZAL intermittently turns itself off.
Here in Hot Perth Western Australia, we predominantly use it for cooling. Some facts that might assist in diagnosis,

Refrig lines approx. 2.5 -3mt long
Running R22
serviced every 1/ 1.5 years
240 Volts

The system works great, Installed in an approx. 30m Sq room relatively high ceilings.
It will work perfectly fine and then just shut down. Sometimes after 25 mins 45 mins or even after 1 - 2 hours. Its completely unpredictable. starting to become annoying.

When you switch it back on we need to wait about 1-3 mins and it starts to cool again.

Any thoughts would be appreciated.
Max