There are no strict rules as recommended temperatures vary for different seasons because every person has different comfort levels.
For most, the most comfortable summer daytime temperature is around 23-25 degrees Celsius. For people experiencing cold weather conditions, their ideal air conditioning heating temperature should be anywhere between 16-20 degrees Celsius. At night, many sleep well with an air conditioner temperature somewhere around 18 degrees Celsius. If you are using your air conditioner for 5-8 hours a day, this would be an ideal temperature to save some bucks on electricity bills. You should also purchase a digital air conditioner thermostat to avoid overcooling or overheating of the rooms and spaces inside your house. There is no specific setting that has been mandated by any government organisation for cold or warmer climates because every individual has his/her own comfort level with regards to the indoor temperature at which they feel most comfortable while working/sleeping. Some people like their rooms extremely cold while some would opt for a warm environment.
If you suffer from occasional breathing difficulties like asthma or respiratory infections, then the ideal AC temperature could be between 16-18 degrees Celsius only.
Because too much dryness can lead to further complications in breathing and cause discomfort to people suffering from such medical conditions.
Also, keep in mind that adjusting your air conditioning unit temperatures is not an exact science, and it all depends on how much time you spend inside the air-conditioned room/space, current outside temperature and wind chill factor (if applicable) and whether or not you use an energy efficient air conditioner.The best set air conditioner temperature for an Australian climate is between 24 degrees Celsius and 26 degrees Celsius. To achieve the most efficient temperature levels, you should also consider the humidity levels inside the room/space where the air con has been installed. Because if humidity levels are very high, then it would be better to decrease the temperature by 1 degree Celsius or so. If you feel that the indoor environment isn't the right temperature and is becoming uncomfortable due to low-humidity conditions, then you can increase the humidity level by using a humidifier to achieve a comfortable temperature. If the outside temperatures are still hotter, it doesn't always imply that your air conditioning unit should be turned down by 2-3 degrees. There could be other factors.
A timer is a great feature on your air conditioner. For example, if your office timings are from 8 am till 6 pm, then you can set an ON timer for 7 am so that your room temperature keeps increasing gradually before you start working in the morning.
As the afternoon draws on, you can set a pre-cooler timer so that your room/space cooling temperature is around the desired level when you enter the room after a break in the afternoon.
For energy efficiency and knock out a few bucks off your electricity bill, you should also keep an auto-restart timer on as you'll avoid wastage of electricity and unnecessary power consumption.
Reverse cycle air conditioners are ideal, as they offer not only cooling but also reverse cycle heating saving on your energy bill as they use chemical refrigerant to absorb heat from outside air (in the summer as well as in the winter) to either heat or cool your home. This makes reverse cycle air conditioning energy efficient and much more adaptable because they're fitted with the inverter technology that ensures the aircon quickly attains the set temperature.
Setting an optimum temperature will also help in electricity savings and money.
This is based on the capacity of your air conditioner and your space/room size. Typical lounge rooms would take anywhere between 10-15 minutes to heat up at the desired temperature. For optimal efficiency consider closing blinds, curtains, doors, and windows to prevent heat loss. You can also set your air conditioner in winter for auto cool/heat mode so that it detects fluctuations in indoor air temperature and accordingly adjusts cooling or heating operations with no manual intervention required.
A typical air conditioner will have a Rated Cooling Capacity, which is the amount of power it takes to cool your room. For example, if you have an 18,000 BTU/hr AC that would be equivalent to 575 watts when operating at 100% efficiency.
This number does not take into account any type of inefficiencies and applies only to ideal conditions (wide-open doors and windows). Real-world energy use is usually double this number or higher. For more information on the energy use of air conditioner's, take a look at the Australian Government's Energy Rating guide.