In most residential split air conditioners, the expansion valve sits near the indoor evaporator coil, typically mounted on the refrigerant line just before it enters the coil. This placement allows the valve to do its job right where it matters: converting warm, high-pressure liquid refrigerant into the cold, low-pressure mist that actually cools your air. That said, the exact location can vary depending on the type of system you have.
Standard Split AC Systems
A standard fixed-speed split AC uses one expansion device, and it’s housed inside the indoor unit. You’ll find it installed on the liquid line (the smaller copper pipe) right before the evaporator coil, sometimes called the “A” coil because of its shape. The valve is usually tucked behind the front panel of the indoor unit alongside the coil, the blower fan, and the air filter.
In simpler or older split systems, the expansion device may not be a valve at all. Many budget units use a capillary tube instead, which is just a long, narrow section of copper tubing that creates a pressure drop without any moving parts. Capillary tubes are also located at the indoor unit, coiled up near the evaporator. They’re cheaper and have no parts to fail, but they can’t adjust to changing conditions the way a valve can.
What the Expansion Valve Actually Does
The refrigeration cycle in your AC has four main components: the compressor, the condenser (outdoor coil), the expansion device, and the evaporator (indoor coil). Refrigerant arrives at the expansion valve as a warm, high-pressure liquid after releasing heat through the outdoor condenser. As it squeezes through the valve’s tiny opening, there’s a sudden, massive drop in pressure. That pressure drop causes the liquid to instantly expand and partially flash into vapor, turning it into an ice-cold, low-pressure mist. This frigid mist then flows into the evaporator coil, where it absorbs heat from your indoor air.
The most common type in residential split systems is the thermostatic expansion valve, often abbreviated as TXV. It uses a small sensing bulb attached to the refrigerant line leaving the evaporator to monitor temperature. When the system needs more cooling, the TXV opens wider to let more refrigerant through. When demand drops, it closes down. This self-regulating behavior keeps the system running efficiently across a range of conditions.
Inverter Systems Use a Different Setup
Modern inverter split ACs, especially multi-zone systems, typically replace the TXV with electronic expansion valves (EEVs or EXVs). These are controlled by the system’s circuit board rather than a mechanical sensing bulb, allowing much more precise refrigerant metering. Variable refrigerant flow (VRF) systems rely on EEVs to monitor both refrigerant conditions and indoor air temperature simultaneously.
Here’s where the location question gets more interesting. In inverter multi-split systems from manufacturers like Daikin, the electronic expansion valves are often located in the outdoor unit rather than indoors. A multi-room Daikin inverter unit, for example, contains one electronic expansion valve for each connected indoor unit, all housed in the outdoor section. A four-room model has four separate electronic expansion valves in the outdoor unit, each controlling refrigerant flow to its corresponding indoor coil. This is a notable difference from standard fixed-speed systems where the expansion device lives indoors.
Some inverter systems also include an additional electronic expansion valve for a bypass circuit in the outdoor unit, which helps manage refrigerant flow during partial-load conditions when not all indoor units are running.
Heat Pump Split Systems
If your split system doubles as a heat pump (providing both cooling and heating), the refrigerant flow reverses direction depending on the mode. This creates a complication: the expansion device needs to be on the high-pressure side before the evaporator, but which coil is the evaporator changes with the mode. In cooling mode, the indoor coil is the evaporator. In heating mode, the outdoor coil becomes the evaporator.
To handle this, heat pump systems often have an expansion device at both the indoor and outdoor units, with check valves or bypass piping that routes refrigerant through the correct one depending on the operating mode. This means a third refrigerant line may be installed between the two sections to accommodate the reversed flow path.
Signs of a Failing Expansion Valve
Because the expansion valve is buried inside one of the units, you can’t easily inspect it yourself. But there are a few signs that point to trouble. Frost or ice buildup on the refrigerant lines near the indoor coil is one of the most visible indicators. A stuck or partially blocked valve restricts refrigerant flow, causing temperatures to drop so low that moisture in the air freezes on contact with the coil or piping.
You might also hear hissing or gurgling sounds coming from the indoor unit as refrigerant struggles to pass through a malfunctioning valve. Fluctuating cooling performance, where the air feels cold one moment and warm the next, can point to a valve that’s opening and closing erratically. Visible refrigerant leaks around the valve connections, though less common, are another red flag.
Replacing an expansion valve requires recovering the refrigerant, brazing new connections, and recharging the system, so it’s a job for a trained technician. If your system is short-cycling, freezing up, or blowing warm air intermittently, a failing expansion valve is one of the likely causes worth investigating.