What Is a Split System Air Conditioner? Your Complete Guide for 2026
Switching to energy-efficient home appliances, such as split system air conditioners, can result in up to 90% savings on electricity bills.
What’s a split system air conditioner, though? It’s an air conditioner with separate indoor and outdoor units. They owe their energy efficiency to a few of their features, including sealed system design, zoned cooling, and better heat exchange.
Split systems come in different sizes and configurations. You’ll work with your installer to customise your setup according to your needs.
In this piece, we’ll cover how split system air conditioners work, the different types available, and the benefits of installing them. We’ll also help you figure out if this solution is a good fit for your home.
Table of Contents
How Does a Split System Air Conditioner Work?
Split systems operate by dividing the cooling workload between two separate units that communicate through refrigerant lines. The indoor unit handles air distribution while the outdoor unit manages heat rejection. Heat rejection is the process of transferring heat from the refrigerant to the outside air.
Components of the Indoor Unit
The indoor unit houses components that work together to deliver conditioned air into your living space. These work in a step-by-step sequence:
- Fan/blower
- Air filter
- Evaporator coil
- Louvres/vanes
Here’s what each does.
- Fan/blower: The fan pulls warm air from the room.
- Air filter: This is a static mesh through which the warm air passes before it reaches the evaporator coil.
- Evaporator coil: The coil is one of the most important components of the AC. It holds chilled refrigerant that absorbs heat from the warm air.
- Louvres/vanes: These are adjustable flaps that direct or usher cooled air into the room. There are two types of louvres; horizontal and vertical. Horizontal ones swing up and down while vertical ones swing left and right.
While the fan, air filter, evaporator coil, and louvres regulate air cooling and distribution, other components function behind the scenes. They’re:
- Thermistor: Helps the system monitor temperature.
- Control board: Receives temperature readings from the thermistor, then uses these readings to coordinate the operations of the fan, compressor, louvres, and other electrical parts.
- Drain tray and drain line: Collect and remove condensed water.
What's in the Outdoor Unit?
The outdoor unit is responsible for supplying refrigerant to the indoor unit and disposing of the absorbed heat. It contains the following:
- Compressor: This is the engine of the entire system. It receives warm, low-pressure refrigerant gas from the indoor unit’s evaporator coil and pressurises it into a high-pressure, high-temperature gas.
- Condenser coil: A network of copper tubes. The high-pressure, high-temperature gaseous refrigerant from the compressor flows through these tubes. As it does, heat is transferred from the refrigerant into the air outdoors. The heat removal lowers the refrigerant’s temperature, converting it back to liquid form.
- Fan: Positioned next to the condenser coil, it blows outdoor air across the coil, speeding up the heat transfer process.
- Expansion valve: By the time the refrigerant passes through this small opening, it’s a high-pressure, warm liquid. Its pressure and temperature drop sharply as it runs along the valve.
- Refrigerant lines: They’re copper pipes connecting the indoor and outdoor units. One line carries warm refrigerant gas from the indoor evaporator coil to the outdoor compressor. The other carries cold refrigerant liquid from the outdoor expansion valve back to the indoor evaporator coil. These lines, along with the electrical wiring that runs alongside them, are the physical connection that makes the split system work as a single coordinated system.
- Control board: The outdoor unit has its own control board that receives temperature data from the indoor unit’s control board.
- Drain tray: Collects water that forms on the outdoor unit’s components.
What Actually Happens During the Refrigeration Cycle?
The outdoor unit’s control board receives temperature data from the indoor unit’s control board. This data tells the outdoor unit how fast the compressor should run.
Then, the compressor pressurises refrigerant (please note that refrigerant is originally in liquid form) till it becomes a high-pressure, hot gas, and passes this hot gas to the condenser coil.
The condenser coil cools the refrigerant by transferring heat from it into the air outside. This cooling process transforms the refrigerant from gas to liquid.
From there, it flows to the expansion valve, where its temperature is dropped even further, then travels through refrigerant lines to the indoor unit’s evaporator coil.
Remember we earlier mentioned that the evaporator coil holds chilled refrigerant? That chilling happens in the expansion valve.
When the indoor unit’s fan pulls warm air from the room into the indoor unit and this warm air travels through the filter into the evaporator coil, the coil already has refrigerant waiting to perform the cooling magic.
What the refrigerant does is to soak up the heat from the warm air. But as it absorbs this heat slowly, the heat makes it evaporate into gas (hence the name “evaporator coil”).
The warm gas travels back through the refrigerant lines to the outdoor unit’s compressor, where it gets pressurised into a high-pressure, high-temperature gas again, and the entire cycle starts over.
How Are the Two Units Connected?
Through refrigerant lines, namely, the liquid line and the suction line.
The liquid line carries cold liquid refrigerant from the outdoor unit to the indoor evaporator coil while the suction line returns cold liquid refrigerant from the outdoor unit to the indoor evaporator coil.
Because both lines are made from copper, they need to be insulated to prevent energy loss and condensation.
For communication signals to be carried from one unit’s control board to another, your electrician would install cables that will connect the indoor unit to the outdoor unit. This wiring runs alongside refrigerant lines through the wall penetration.
Different Types of Split System Air Conditioners
Split system air conditioners come in several configurations. Each one is designed to meet specific needs.
The standard split system is a 1:1 pair; only one indoor unit is connected to only one outdoor unit. Installation is straightforward, and there’s no need for expensive ductwork, but the system can only cool one zone or room at a time.
Standard split system ACs are an excellent fit for small residential homes. Each room in the house gets its own dedicated, separate air conditioner.
In a multi-split system, you can connect as many as five indoor units to a single outdoor unit. Most multi-split ACs are ductless, providing air conditioning for several zones at a time.
You don’t need to install the exact indoor units of the same style and capacity in all rooms.
For example, you could install a high-capacity wall-mounted unit in the living room and a compact ceiling cassette in the bedroom. Each will be connected to the same outdoor unit, yet have its own remote control and independent temperature settings.
Families who don’t want their outside walls cluttered with outdoor units appreciate multi-split systems.
Heat pump split systems are capable of heating and cooling. They function like cooling-only split systems, with separate indoor and outdoor units, but can also reverse the cooling cycle to transfer heat from outside air into the room. Their capacity to reverse the cycle is why they’re also called reverse-cycle air conditioners.
Reverse-cycle ACs are more popular than cooling-only systems in Australia. Information from the Energy Rating Registration Database shows that 62.9% of registered AC models in our country are reverse-cycle!
In warmer months, you configure the AC’s settings to remove heat from indoor air. When winter approaches, you simply change temperature settings to extract heat from outdoor air and deliver it indoors.
High-efficiency models achieve up to 7 stars on the ZERL scale and deliver consistent year-round comfort while bringing down your electricity bills.
“Ducting” is a technical term for the network of insulated tubes or channels that run through the ceiling or floor cavity of a building.
Ducted Systems
If a split system is described as “ducted,” that means it comprises a sole, central indoor unit and a single outdoor unit serving all rooms in the home. A network of ducts running through the ceiling or floor cavity connects the central indoor unit to vents in each room, distributing conditioned air throughout the home.
Ductless Systems
A ductless system doesn’t rely on ducting for conditioned air distribution. It’s of two types:
- Single-split: Like we explained earlier, each room has its own indoor unit and outdoor unit.
- Multi-split: The installer fits individual rooms with independent indoor units, but all units in the home are connected to a single, central outdoor unit.
Ducted systems are more aesthetically pleasing because the central indoor unit is hidden in the roof space and the only visible elements in each room are small ceiling vents, so there are no wall-mounted units taking up visual space. However, they may not be as energy-efficient as ductless options due to duct-related heat loss.
Benefits of Split System Air Conditioners
Split systems offer measurable advantages.
A split system’s efficiency depends on the model design, installation quality, room conditions, temperature settings, and other factors. Generally, however, ductless split systems are more efficient than ducted ones.
The Australian Department of Climate Change, Energy, the Environment and Water recommends ductless air conditioners for households aiming to lower their utility bills.
If a split system is designed with inverter technology, it delivers even greater energy efficiency because it can automatically adjust the compressor’s speed to match the target temperature.
Indoor units’ noise levels can be as low as 19–21 decibels. This figure is quieter than a library and well below the WHO’s recommended nighttime noise guideline of 30 dB. However, an indoor unit won’t be that quiet in every situation. Noise levels depend specifically on fan speed, unit type, model design, operating mode, and cooling load.
The same split system might be very quiet when cooling a small bedroom from 26°C to 24°C at night but much louder when cooling a hotter sun-facing room from 32°C to 22°C in the afternoon.
Outdoor units are usually much noisier than indoor units since they contain the components that do much of the mechanical work, particularly the compressor and the outdoor fan.
If your split-system air conditioner is ductless, your installer will only bore a 2–3 inch hole through your wall to connect the indoor and outdoor units. Your quote might also be lower, especially if you’re installing an air conditioner in just one or a few rooms.
Manufacturers design indoor units for different mounting styles. When shopping, you’ll see options that are supposed to sit below the ceiling, high on a wall, in the ceiling, or near floor level. Share your interior design preferences with your installer and work with them to find the best type of unit for each cooling zone.
Each indoor unit operates with its own thermostat, which means you’re able to set different temperatures in different rooms. You only condition spaces you’re using rather than cooling your entire home. This targeted approach reduces energy waste.
What Is the Lifespan of a Split System Air Conditioner?
High-quality split systems typically last between 10 and 15 years when you maintain them properly, while premium systems can reach up to 20 years or longer.
One major factor is the quality of the air conditioner itself. Systems made with premium components, such as variable-speed compressors, corrosion-resistant coils, and well-built fan motors, are more likely to last longer than those engineered with lower-grade parts.
Another consideration is installation quality. Let’s say that an installer, when routeing refrigerant lines through the wall, bends a copper pipe too sharply and partially crushes it. That kink makes the pipe narrower than it should be. Although it still carries refrigerant, the restriction might make the compressor run longer than it should to achieve the target temperature. This extra strain on the compressor can wear it down early.
Climate conditions affect performance as well. In extreme-temperature and high-humidity regions, air conditioners have to work harder to reach the target temperature, particularly when the target is far from the current temperature. A person who lives in an inland area that reaches 40°C and consistently sets their target indoor temperature to 16°C may not get as many years from their system as someone who uses the same model in milder conditions.
Usage patterns influence system longevity too. Running your air con at a target temperature that’s significantly far from the normal room temperature increases its workload and places it under greater stress over time.
Maintaining Your Split System Air Conditioner
Regular Maintenance Tips
- Clean air filters once a month during periods when you run the AC for prolonged durations.
- Hire a professional to service the system at least once a year; they’ll catch budding issues early.
- Wash dirt off the outdoor coil when the system is off. The cleaner the coil is, the easier it is for the outdoor unit to reject heat. A gentle rinse with a garden hose is enough. Don’t pressure-wash the coil, open any panels, or tamper with electrical wiring.
Common Issues and Solutions
| Issue | Possible Causes | Solutions to Try |
| The room is not cooling properly. | The filters may be dirty, the outdoor coil may be blocked, or the unit may be too small for the room. | Clean the filters, check that the outdoor unit has clear airflow, and call a technician if performance does not improve. |
| Water is dripping from the indoor unit | The drain line may be blocked or poorly sloped, causing condensed water to back up. | Turn the system off and arrange for servicing, especially if water is near electrical parts. |
| The unit smells musty | Moisture, dust, or mould may have built up inside the indoor unit. | Clean the filters first. If the smell persists, book a professional cleaning session. |
| The system is noisier than usual | The fan may be obstructed or the louvres may not be moving properly. | Check for visible debris around the unit. If the noise continues, get it inspected. |
Is a Split System Air Conditioner Right for Your Home?
Split systems are a smart conditioning solution in most cases. Before completing any purchase, reach out to an installer with details about your space, budget, location, cooling (and heating needs, if applicable), and how much you’d like to save on energy bills.
We simplify the process at BG Electrical. Just tell us your suburb, indicate that you want air conditioning installation, and provide a bit more information about what you need. We’ll send you a free quote ASAP.
For personalised guidance on system selection and professional installation, call us at 32791835 or 0434288108.