What is an inverter compressor?

What an inverter does

An inverter controls and varies the speed of the compressor motor. The compressor sits in the outdoor unit and does the heavy work of heating or cooling your home.

It works much like the accelerator in a car. An inverter system slows the compressor down and speeds it up as needed to hold the comfort setting you have chosen. Instead of running flat out, it runs at whatever speed the room needs at that moment.

Once the room reaches the temperature you set, the compressor keeps running at a low speed to hold it there. It regulates the temperature continuously rather than in bursts.

Inverter versus fixed speed

A fixed speed system, also called a constant speed system, has a compressor that runs at one speed. It runs at full power until the room reaches the set temperature, switches off, waits for the room to drift away from that setting, then starts again at full power.

That start and stop cycle is where the temperature swings come from. The room is a little too warm, then a little too cool, then too warm again.

An inverter system avoids those sharp swings in load. Because it can run slowly, it holds the room close to the set temperature without the fluctuations of a fixed speed system.

What you notice at home

The difference shows up in four ways.

• A more precise room temperature. The system holds your setting steadily rather than cycling above and below it.
• Quieter operation. Speed control of the outdoor unit means it is not always running at full power. This matters most at night in residential areas, where the outdoor unit may sit near a bedroom or a neighbour's window.
• Lower running cost. An inverter system is more efficient than a fixed speed unit, and it can reach the temperature you want more quickly.
• Longer life. Removing the sharp fluctuations in load reduces wear on parts, which makes the system more durable and reliable over its working life.

Purchase price and running cost

An inverter system may cost more to buy than a constant speed system. ACDA's view is that the higher purchase price is balanced by lower energy bills overall. How quickly that adds up depends on how much you use the system and how you run it.

When you compare quotes, look at the running cost as well as the price on the page. The Energy Rating Label is the fair way to compare the efficiency of different models. See our guides to energy star ratings and what a proper quote includes.

Getting the most from an inverter system

Set the temperature you want and let the system hold it. Turning it on and off, or changing the setting often, works against the way an inverter is designed to run.

On a hot day, turn the system on early, before the room gets hot. That avoids having to run at full power to bring the room down, and the air conditioner operates more efficiently when the outside air is cooler.

Our set point guide covers the settings that keep running costs down, and getting your air conditioning ready for summer covers the checks before the hot weather.

Before you compare quotes

• Ask whether each system quoted is an inverter or fixed speed model.
• Ask how quiet the outdoor unit runs at night if it will sit near a bedroom.
• Weigh the purchase price against lower running costs over the years you will own it.
• Check the Energy Rating Label when comparing models.
• Set a temperature and let the system hold it rather than switching it on and off.
• On a hot day, turn the system on early, before the room heats up.
• Use an accredited dealer to advise, supply, install and service the system.

An accredited member can tell you whether the systems in your quote are inverter models and what that means for the way your home is used. Find an accredited dealer near you.