There are two important components of the window AC – the compressor and the Fan motor. The Compressor consumes 90 percent of the electricity whereas the fan motor consumption is only 10 percent. The compressor is backbone of the air conditioner as this is the component that causes cooling. It compresses the gas causing it to become hot, which is then condensed into a liquid through a set of coils. This cools the air around it.

There are two types of compressors used in window ACs – reciprocating and rotary.

Reciprocating compressor - It compresses the air by sliding the piston over the cylinder. Air conditioners fitted with a reciprocating compressor are generally less expensive but are not as efficient and silent as the ACs with the rotary compressor.

The rotary compressor is expensive as compared to a reciprocating compressor, however, it makes up for that cost by saving more on power as compared to a reciprocating compressor.

Energy Efficiency Ratio measures the cooling efficiency of the air conditioner as compared to the power it consumes. It is the ratio of the cooling capacity in BTU/hr to its electricity consumption in watts. Models with a higher EER save on your electricity bills but are priced a little higher than ones with lower EER. An EER of nine and above is considered good. In 2007 The Bureau of Energy Efficiency (BEE) has decided to introduce the system of Standards and Labeling, which is a method of rating the electrical gadgets based on their energy efficiency. A gadget with high-energy efficiency would be accorded five stars while that with least energy would get a single star. The gadgets would have a label certified by the BEE indicating the number of energy efficient stars accorded to the gadget and also the approximate quantum of energy consumed by the gadget in a year. Some of the leading brands like Carrier, Voltas, LG and Samsung have got some of their window air conditioner models rated for BEE Star Rating.

A filter purifies the air that goes through the air conditioner. There are different types of filters that remove dust, germs, bacteria, odour, etc. Deodorising filters remove dust particles and dirt; anti-fungal filters clean the air and remove germs and bacteria thus reducing respiratory problems. The Electrostatic filter releases positive ions, which ionise the negative ions of dust and static electricity giving you a clean, dust free environment. Slide-in and Slide-out filters allow easy maintenance as they can be removed for cleaning without opening or dismantling the entire machine. If you smoke or live in an air-polluted area that is prone to dust, this would be an important feature to consider.

The body and framework of air conditioners is prone to corrosion especially as one part of it is outside and is exposed to rain, moisture, dust, etc. However, if the exterior is made of galvanised steel or is powder coated it helps in protecting the unit from corrosion and extends the life of the body.

If there is a power failure or if the air conditioner has been disconnected, you may have to reset and programme all the cooling functions and features that you originally had. An air conditioner with the auto restart facility starts automatically and restores the original settings when the power is restored. This feature is beneficial in areas where power supply is irregular.

Don't need to go into why this is useful but it becomes a must-have if your AC is placed at a height. Of course, most of us cannot imagine an appliance without a remote control, as it would mean having to get up each time to change settings.

The timer lets you to set the air conditioner to begin cooling at any time, whether you are home or not. It is also helpful to shut off during the middle of the night when it gets very cold.

Air conditioners with rotary compressors generally make less noise than a reciprocating compressor. The noise level in a window AC ranges fro 40 to 60 db. The lower the better, however, higher the capacity of the air-conditioner, more the decibels.

Other Features

Sleep Mode – Air conditioner with sleep modes automatically adjusts the temperature in different stages at night to save power and keep the room comfortable for sleeping.

Dry Mode – This feature is useful in high humidity conditions like coastal parts of India, you can switch to dry mode wherein the fan speed of the machine automatically becomes low which helps in removing moisture. This feature maintains low moisture level, thus keeps room filled with fresh air.