The compressor and its motor are manufactured to operate at constant speed or single speed only. In simple terms, it is either in the on (Full Power) or off (No Power) mode.
Therefore for Non Inverter, you will actually feel the air conditioner blowing cold air one moment and normal wind at another.
Due to this operating principle, the electrical consumption is higher and the compressor tends to spoil more easily because of the frequent start-stop. And there is no part load capabilities.
1) Orginally, Non Inverter air con uses only one big compressor linking to a few indoor units. Thus no matter how many rooms u use, you are always using the full capacity of the compressor. This is actually very inefficient. For example, the electrical comsumption will be the same when using 1 room and 3 rooms.
2) But as technology improved, most of the Non Inverter air conditioners in the market are using 2 compressors. For example, a System 3 will have 1 compressor of 8500 btu and the other at 12000 btu. The 8500 btu will be connected to 1 indoor unit while the 12000 btu will be connected to 2 indoor units. Therefore when operating 1 room, you will be using only 1 compressor.
** If you are using the 2 indoor units that are connected to the 12000 btu compressor, you will only get max 6000 btu each. **
3) May it be new or old, as long as it is a Non Inverter, you will get the 'cut in' and 'cut out' of the compressor. In other words, everytime the room reaches the pre-set temperature, the compressor will stop working. And when it senses an increase in temperature, it will start running again. Thus through out the night, you will experience the 'start and stop' of the compressor. In addition to that, the temperature will fluctuate as the indoor unit changes from 'COOL' to 'FAN' mode accordding to the 'start - stop' of the compressors.
4) Due to the frequently start-stop of the compressor, more eletricity will be comsumed as more power is needed to start the system all over again whenever it stopped. In addition, the compressor will also have a shorter life span.
5) Most Non Inverter Multi Split Systems have 'standard' combinations. For example, Sys 3 will be 9+9+9. When you required other combinations, you usually have to pay more as it may require a high capacity outdoor unit. And the largest indoor unit capacity for Multi Split System is 12k btu.