Hi,
If you are installing a new air conditioner, and had opted for new piping, than it is important that you observe the installers to ensure that they do not joint the pipes.
Discuss this requirement with the seller and have it written in your order that no jointing is acceptable except at the FCU and Condenser and to use flared joints. Some worker braze the pipe at the FCU to save them the work to properly route the pipes.
Brazing of the pipes is not acceptable and you should be consulted if worker which to do brazing. Never Never allow them to braze the pipes.
As you are paying for the new pipe, there is no reason why the new pipe need to be jointed. New pipe comes at a length of 15m and this is sufficient for most houses in Singapore.
Jointing of new pipes are done when workers salvage left over new pipes from other installation to save cost. Some pipes may have a few joints from shorter pipes. When pipes are inserted into the insulation, it becomes difficult for the customers to check for brazed joints. Workers will normally insert the pipes into the insulation when you are not around or during lunch time when no one is watching them.
Have it in your agreement that you wish to inspect the new pipe before they are inserted into the insulation.
In Singapore, all air conditioner joint that are brazed are inappropriately done, ie without the use of nitrogen gas and as a result may cause serious failure to the system with expensive repair or even complete change of the whole system.
Attached is a link showing what happened when copper pipe is brazed with and without nitrogen.
https://youtu.be/Bpqxbc9XQ5Y
Air conditioner system consist of parts that have very fine holes in the control devices and scaling from brazed pipe without using nitrogen can easily choke the system.
So NEVER NEVER allow your new pipes to be brazed joint by the worker at any cost. Stop them, or reject the pipe and show them your agreement that you have with the seller.
The above are my opinion and hope that they are helpful.