A split AC is an air conditioning system divided into two connected units: an outdoor unit containing the compressor and condenser, and an indoor unit containing the evaporator coil and blower. Refrigerant lines and a small conduit for wiring and condensate drainage connect the two through a hole in the exterior wall. The "split" refers to this physical separation, which distinguishes these systems from window units and packaged systems that house everything in a single cabinet.
Three Configurations Under One Name
The term "split AC" covers three distinct system types that differ in how the indoor unit distributes air:
Configuration |
Indoor Unit |
Ductwork |
Zones |
Typical SEER2 Range |
Ducted split |
Air handler or furnace + evaporator coil |
Yes, full duct system |
Whole home (single zone unless zoning dampers added) |
13.4-24 |
Ductless mini-split |
Wall, ceiling, or floor-mounted cassette |
None |
Single room per indoor unit |
16-30+ |
Multi-zone mini-split |
Multiple indoor units connected to one outdoor unit |
None |
2-8 rooms independently |
16-25+ |
Ductless mini-splits achieve higher efficiency ratings because conditioned air travels directly into the room with no duct losses. Ducted systems can lose 20-30% of cooling output through leaky or uninsulated ductwork before the air reaches the living space.
These three configurations sit alongside window units, portable ACs, and packaged systems in the full range of air conditioner types, each with different costs, installation, and performance trade-offs.
How Indoor Units Are Controlled
Ducted split systems connect to a wall thermostat (programmable or smart) through low-voltage wiring. The thermostat reads room temperature and signals the system to cycle on or off.
Ductless mini-splits and multi-zone systems ship with handheld infrared remotes instead. The remote communicates with the receiver on the indoor unit to control temperature, fan speed, swing direction, and mode. There is no wiring for a traditional wall thermostat. This IR-based control is the reason most ductless units lack built-in scheduling, geofencing, or energy tracking out of the box, and why retrofit smart controllers exist to add those capabilities over WiFi.
Split AC vs. Packaged System
In a packaged system, the compressor, condenser, evaporator, and blower all sit in a single outdoor cabinet, with ductwork running from that cabinet into the home. Packaged systems are common where indoor space is limited (no basement, no attic, no utility closet). Split systems offer higher efficiency ceilings and more flexibility in component placement, but require space for both an indoor and outdoor unit, plus the refrigerant line set connecting them.