An air conditioning system blows the same temperature air.
If you put the temperature on your handset or panel down to 18 degrees, it will not blow any colder air out. What it is actually trying to achieve it to get the whole area down to 18 degrees. Which is totally unnecessary.
In the hot summer months this means the system will continuously run, and will cause larger electricity bills, and overrun your unit. It will also cause the unit to condense more water which needs to drain, and this can lead to some A/C units leaking water, as the water can not drain away quick enough , so the water will back up the drain tube, and can leak from the internal unit.
The temperature you need to set the handset or panel is around 23-25 degrees. Which is more than adequate in the summer months.
Do not set the vents on the internal system (split A/C units) on oscillating, or in the down position in the summer months. To get the most efficient use, the best position for the vents on the interior unit should be set in the highest position.
WHY ?Because cold air drops down, so when putting the vents in high position, the air blows upwards, and cools the whole area evenly. Then the sensors on the unit pick up the return temperature of the room, and the external unit will slow down , and go into low running mode as it should, saving on running costs.