Electricity (units) is used by 1.5 ton split AC?

Around 1.5 units per hour, provided the compressor is on.

But that is a rough estimate, your actual power consumption varies every single second. Let's dive in a little deeper and see how these things relate to each other.

If you carefully look at your air conditioning unit, you'll probably see a label like this :

The power rating printed on such a label is when the AC is under a stable load, the current is constant, the compressor is working, there's no back emf being produced in the induction coils, and above all the supply voltage is exactly equal to 230 volts at 50 Hz.

In this stable state, the AC unit is consuming 1.5 units of electricity per hour.

That said, not always is the compressor running. If your AC has a thermostat and a temperature setting, once the ambient room temperature reaches to the set limit, the compressor shuts off and only the circulating fans work.

In this case the power consumption is almost equal to a ceiling fan, with my test bench, I got readings around 0.3 amps at 230 volts. That is equal to 0.06 units per hour, almost equal to a 80 watt incandescent bulb.

Another test I conducted : Under extreme load, at a room temperature of about 32 degree Celsius, the power consumption rose to almost 1.8 units per hour, or 1800 watts.

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How do you calculate your power consumption :

The commercial unit of electricity is kWh, also called as BTU (Board of trade Unit), which equals to one kilowatt load used for 1 hour.

Units = Power in Watts * time in seconds / 3600000

Or

Units = Power in Watts * time in hours / 1000

Or

Units = Power in kiloWatts * time in hours

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You can guess the power consumption by these steps :

For while the compressor is working :

• Note down the peak power usage from the label of your AC unit.
• Now do the following maths :
  Units Consumed = Power * Hours of usage / 1000
• Calculate your projected consumption part 1

For while the circulating fan is working :

• Take the power usage in this case as a average of 80 W.
• Do the following maths :
  Units consumed = 80 * Hours of usage while the compressor is off / 1000
• Calculate your projected consumption part 2

Try this for the average time you use your air conditioner in a day, and add the two to get the daily units consumption. Multiply this with the cost of 1 unit of electricity (around Rs. 6) and you'll get the bill for a single day. Multiply by 30 to get the monthly expenditure.

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For example :

I use my AC unit for around 14 hours a day, at 24 degree Celsius.

During the 14 hours cycle, my compressor works for about 4 hours, while for the rest 10 hours, only the fan works.

Consumption Part 1 : 1500 * 4 /1000 = 6 units
Consumption Part 2 : 80* 10 /1000 = 0.8 units
Total Consumption : = 6.8 units
Bill for a single day : = 6.8 * 6 = 40.8
Bill for a month : = 40.8 * 30 = Rs. 1224

But the fact is, that never do you get the exact 230 V supply, nor does the operating conditions remain the same, so for the projected output, add a uncertainty factor of 20 % positive, and the value will be quite close to the actual consumption.

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Keep in mind that this varies from AC to AC, and to get a fairly accurate reading is almost impossible.