Fridge Freezer trips RCD exactly 30 mins after start up… every time

Hello.

Our four year old Haier HRF-62D*6 American style fridge freezer trips the circuit’s RCD exactly thirty minutes after power up, every time. I’ve done all I can, including:

1) Wire fridge to another circuit with different RCD. (Same result, so it’s not due to dodgy RCD)
2) Empty all water out of tray at the bottom (it was full), clean all dust off electrical stuff, ensure all is dry
3) Taken off service grill (bottom back) and electrics cover (top) to see what happened at exactly thirty minutes… no extra info gained

I have the service and user manual but they have been of little help.

Any pointers appreciated. What would be really handy to know is what it is that is supposed to kick in after exactly thirty minutes of operation.

Thanks.