Can I turn off my split AC/heating system?

Yes, isolating power to a split AC system at the fused spur (FCU) is safe when done correctly.

From an electrical perspective, switching the power supply externally is equivalent to the internal control system turning the compressor on or off.

As confirmed by a Senior Electrical Engineer at Syska Hennessey:

“Switching the power on and off does the same thing as what would happen when the motor controller turns the compressor on or off.”

When power is restored, the system will experience a temporary inrush current as the compressor motor starts. This is normal behaviour and is already accounted for in system design.