Just to share recent experience and tips replacing an old air conditioner.

replaced an air-conn (non-inverter) in a condo with an inverter unit and used the existing pipes and drain already inside the wall.

 

Like many new build houses/condos, the indoor unit is in the middle of a feature wall and not adjacent to the outside unit, all pipes are inside the wall. Most of the cowboy installers will turn up and say that the old pipes cannot be used, they need to run ducting etc, this isn't true and a good installer can reconnect to the existing pipes, adaptor, solder, extend etc (with only some minor patching to wall).

 

The second issue is, if upgrading from a non-inverter to an inverter unit, a third signal wire is required from indoor unit to outdoor unit. Most old units only have active and neutral going to the outside unit, so the installer may need to get creative running/hiding the 3rd wire or stealing neutral from close by etc.

A decent ground is also required for many inverter control circuits to provide surge protection and noise filtering.