How Does A Mini Split System Work?

How Does A Mini Split Syst

A mini-split system, sometimes referred to as a ductless mini-split or a ductless heat pump, is a kind of HVAC (Heating, Ventilation and Air Conditioning) system made to supply heating and cooling to specific rooms or zones inside a building. It provides a versatile and effective climate control solution, particularly in circumstances where conventional ducted systems are unfeasible. In this comprehensive guide, we’ll delve into the step-by-step workings of a mini-split system, exploring its components, operation, and advantages.

Mini-Split System

A mini-split system consists of two main components: indoor and outdoor units. These components work together to transfer heat from one location to another, providing cooling or heating depending on the desired climate control.

Components Of A Mini-Split System

A) Indoor Unit

The indoor unit, typically wall-mounted or ceiling-mounted, delivers conditioned air to the designated zone. It contains the evaporator coil, a fan, and various control components.

Evaporator Coil

As a heat exchanger, the evaporator coil facilitates the heat exchange process.Warm inside air is blasted over the cold evaporator coil when the system is in cooling mode, which causes heat to be absorbed from the air and transferred to the refrigerant inside the coil. Consequently, the indoor air gets cooler and cosier. 


The Fan in the indoor unit circulates air over the evaporator coil. It draws warm indoor air into the unit, passes it over the cooled evaporator coil, and then distributes the cooled air back into the room.

Control Components

The indoor unit has controls that allow users to set the desired temperature, fan speed, and operating mode (cooling or heating). Some advanced mini-split systems also offer features like programmable timers and remote control capabilities.

B) Outdoor Unit

The outdoor unit houses the condenser coil, compressor, and other crucial components necessary for the heat exchange process.

Condenser Coil

The outdoor unit’s condenser coil serves as a heat exchanger during the heat exchange operation. When the system is cooling, heat is released to the outside air by the refrigerant in the condenser coil, causing the refrigerant to condense and cool.


The compressor is often referred to as the “heart” of the mini-split system. It plays a pivotal role in the heat exchange cycle by compressing the low-pressure, low-temperature refrigerant vapor from the evaporator coil into a high-pressure, high-temperature vapor. This compressed vapor is then sent to the condenser coil to release heat.

Expansion Valve

Located between the indoor and outdoor units, the expansion valve regulates refrigerant flow into the evaporator coil. As the high-pressure refrigerant flows through the expansion valve, it undergoes a rapid pressure drop, which causes it to expand and evaporate, thus absorbing heat from the indoor air.

C) Refrigerant Lines And Tubing

The refrigerant lines that connect the indoor and outdoor units are constructed of copper tubing, which transports the refrigerant between the evaporator and condenser coils.These lines distribute the refrigerant (in liquid and vapour form) in all of its states throughout the system.

1.Cooling Mode Operation

Now that we understand the components let’s explore how a mini-split system operates in cooling mode:

Step 1: Indoor Unit Operation

  1. The indoor unit’s Fan draws warm indoor air into the unit.
  2. The warm indoor air passes over the cold evaporator coil, causing the refrigerant within the coil to absorb heat from the air.
  3. As heat is absorbed, the indoor air becomes cooler and more comfortable.
  4. The Fan then distributes the cooled air back into the room.

Step 2: Refrigerant Flow

  1. The refrigerant, now in a low-pressure, low-temperature vapor state, is drawn into the compressor located in the outdoor unit.
  2. The compressor compresses the refrigerant, raising its temperature and pressure.
  3. High-pressure, high-temperature refrigerant is vaporized through the condenser coil and condenses into high-pressure liquid, releasing heat into the air outdoors.

Step 3: Expansion Valve

  1. Through the expansion valve, the high-pressure liquid refrigerant is rapidly reduced in pressure.
  2. This pressure drop causes the refrigerant to expand and evaporate, absorbing heat from the indoor air again.

Step 4: Cycle Continuation

The refrigerant completes the cycle by returning to the indoor unit, which absorbs heat from the indoor air. This continuous cycle maintains the desired indoor temperature by removing heat from the indoor environment and releasing it outdoors.

2. Heating Mode Operation

A mini-split system can also operate in heating mode, making it a versatile year-round climate control solution. The heating mode operation is essentially the reverse of the cooling mode operation:

Step 1: Indoor Unit Operation

  1. The indoor unit’s Fan draws cool indoor air into the unit.
  2. The cool indoor air passes over the warm evaporator coil, causing the refrigerant within the coil to release heat into the air.
  3. As heat is released, the indoor air becomes warmer and more comfortable.
  4. The Fan then distributes the heated air back into the room.

Step 2: Refrigerant Flow

  1. The refrigerant, now in a low-pressure, low-temperature liquid state, is drawn into the compressor located in the outdoor unit.
  2. The compressor compresses the refrigerant, raising its temperature and pressure.
  3. The high-pressure, high-temperature vaporized refrigerant flows through the condenser coil, releasing heat to the outdoor air and causing the refrigerant to condense into a high-pressure liquid state.

Step 3: Expansion Valve

  1. When a liquid refrigerant flows through an expansion valve, its pressure is rapidly reduced.
  2. This pressure drop causes the refrigerant to expand and evaporate, absorbing heat from the outdoor air.

Step 4: Cycle Continuation

The refrigerant completes the cycle by returning to the indoor unit, releasing heat into the indoor air. This cycle ensures the indoor environment remains warm and comfortable even in colder weather.

Positive Aspects Of Mini-Split Systems

There are several advantages to using a mini-split system over a traditional HVAC system:

  • Zoned Cooling and Heating: Mini-splits allow for individualized temperature control in different rooms or zones, optimizing comfort and energy efficiency.
  • No Ductwork Required: Mini-splits are ductless systems, eliminating the need for costly duct installation and potential energy loss associated with ducts.
  • Energy Efficiency: Unlike central HVAC systems, ductless systems are more energy-efficient since they do not suffer from energy losses caused by ducts. 
  • Flexible Installation:Mini-splits are easy to install and can be put on walls or ceilings, giving you a range of room layout possibilities.
  • Precise Temperature Control: Mini-splits enable precise temperature adjustments, reducing energy waste and providing tailored comfort.
  • Year-Round Comfort: Mini-splits offer cooling and heating capabilities, making them suitable for year-round use.
  • Quiet Operation: These systems operate quietly, ensuring a peaceful indoor environment.
  • Reduced Environmental Impact: Many modern mini-split systems use environmentally friendly refrigerants and are designed with energy-saving features.

Maintenance And Care

Regular maintenance is required to guarantee that your mini-split system operates efficiently and reliably. Here are some suggestions for maintenance:

  • Filter Cleaning: To maintain adequate airflow and indoor air quality, clean or replace the air filters on a regular basis.
  • Coil Cleaning: Clean indoor and outdoor coils to facilitate efficient heat exchange.
  • Check for Leaks: Inspect refrigerant lines and connections for leaks, as refrigerant leaks can impact system performance.
  • Clear Obstructions: Ensure that the outdoor unit is free from debris, vegetation, and other obstructions that can hinder airflow.
  • Professional Maintenance: Schedule annual professional maintenance to check for issues and optimize system performance.

Who Should Select A Mini-Split Air Conditioning System?

A mini-split AC system is an ideal choice for several situations and individuals:

  1. Individuals in Rental Properties: Renters who cannot modify existing HVAC systems can benefit from mini-splits, as they can be installed without altering the property’s structure.
  2. Homeowners: Homeowners looking to add climate control to specific rooms or areas, such as home offices or additions, can benefit from mini-splits’ flexibility.
  3. Older Homes: Older homes without existing ductwork can be challenging to retrofit with traditional HVAC systems. Mini-splits offer a practical solution without the need for extensive renovations.
  4. Energy-Conscious Individuals: Those seeking energy efficiency can appreciate mini-splits, as zoned heating and cooling reduce energy consumption by only conditioning the spaces in use.
  5. Commercial Spaces: Businesses needing targeted climate control for specific areas, like server rooms or retail spaces, can benefit from the precision of mini-split systems.
  6. Allergy and Asthma Sufferers: A mini-split system with efficient air filtration options can improve the indoor air quality of those with respiratory issues.
  7. Multi-Unit Buildings: In multi-unit buildings or apartments, mini-splits offer individualized comfort control without affecting neighbors.
  8. Climate with Seasonal Variations: Regions with varying climate conditions can benefit from mini-split systems’ year-round cooling and heating capabilities.
  9. Eco-Friendly Consumers: Those concerned about environmental impact may prefer mini-splits with energy-efficient features and eco-friendly refrigerants.
  10. Home Renovators: Individuals renovating their homes can incorporate mini-splits into new areas without requiring extensive ductwork installation.
  11. Home Additions: When adding new rooms or spaces to a home, mini-splits provide a cost-effective and efficient solution for heating and cooling.
  12. Home Offices: Mini-splits offer personalized comfort for home offices, ensuring a conducive working environment.
  13. Historic Buildings: Historical structures can be preserved structurally with mini-splits without requiring significant structural changes.
  14. Noise-Sensitive Environments: Mini-splits operate quietly, making them suitable for bedrooms, libraries, and other noise-sensitive areas.

In summary, a mini-split AC system is an excellent choice for those seeking flexibility, energy efficiency, targeted climate control, and installation versatility in various residential and commercial contexts.

You might be interested to see the differences between mini split and central air conditioning.

Frequently Asked Questions

How Do I Maintain A Mini-Split System?

Regular maintenance involves:

  • Cleaning or replacing filters.
  • Keeping coils clear of debris.
  • Checking for leaks.
  • Scheduling annual professional inspections.

Can Mini-Split Systems Be Used Year-Round? 

Yes, mini-split systems offer cooling and heating modes, making them suitable for maintaining comfort throughout all seasons.

What Are The Environmental Benefits Of Mini-Split Systems?

Modern mini-splits often use eco-friendly refrigerants and energy-saving features, contributing to reduced environmental impact compared to traditional HVAC systems.


Mini-split systems offer an innovative approach to heating and cooling that delivers precise comfort control, energy efficiency, and installation flexibility. By understanding the step-by-step process of how these systems work, you can make informed decisions about their suitability for your specific climate control needs. Whether cooling down during hot summer days or staying warm in winter, a mini-split system can provide the comfort you desire while minimizing energy consumption and environmental impact.

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About the author


I am Ben , a seasoned HVAC specialist with over 6 of experience in the HVAC industry. I holds HVAC Certification and has a proven track record in providing expert advice on HVAC systems.