What Is Inside an Air Conditioner? A Tour of the Parts
A home air conditioner is a team of parts: a thermostat, vents, a filter, a fan, a cold coil, a drain, ducts, copper pipes and an outside unit. Follow the air on this tour to meet each one.
Many of these parts are hidden in the attic, a closet or outside, so we drew a map for you.
The tour, stop by stop
Stop 1: The thermostat (the boss)
The thermostat is the box on the wall. It has a thermometer inside that feels the room’s temperature. When the room gets warmer than the number a grown-up picked, it sends a signal: “Start cooling!” When the room is cool enough, it says, “Rest now.”
Look for: the number on its screen or dial.
Stop 2: The return vent (the front door)
The return vent is the big air grille, usually on a wall or ceiling in a hallway. This is where the AC breathes in. The blower pulls air from your rooms in through here. Air needs this door to get back to the machine.
Look for: the biggest vent in your home. Your job: keep furniture, toys and laundry away from it.
Stop 3: The filter (the doormat)
The air goes through a filter before anything else. It catches dust, fur and lint. In some homes, the filter sits right behind the return vent grille. In others, it slides into the indoor unit.
Look for: an arrow on its edge pointing toward the machine. Hands: grown-ups change it.
Stop 4: The blower (the big fan)
The blower is a fan shaped like a hamster wheel. It spins inside the indoor unit, pulling air in through the return and pushing it out to your rooms. The whoosh you hear at a vent is the blower at work.
Stop 5: The indoor coil (the heat grabber)
The indoor coil is a set of metal tubes with thin fins, kept very cold by refrigerant flowing inside. Warm air blows across it, and heat jumps from the air into the coil. The air comes out cooler and drier.
Pro level: why is it shaped like an A?
Many indoor coils are bent into an A shape. That fits more coil into a small box, so more air can touch more cold metal.
Stop 6: The drain pan and drain line (the water slide)
Water vapor in the air condenses on the cold coil and drips into a pan. From there, it flows down a plastic pipe called the drain line. Often it ends outside, near the house, where you might see drips on hot days.
Your job: if you ever see water where it shouldn’t be, like on a ceiling, a wall or a closet floor, tell a grown-up.
Stop 7: The ducts and supply vents (the hallways and windows)
Ducts are big tubes, round or square, that carry the cool air from the indoor unit to every room. The air comes out of supply vents. In most Austin homes they’re in the ceiling, with slats you can see from below.
Look for: the supply vent in your room’s ceiling. When the AC runs, stand under it and feel the air coming down.
Stop 8: The copper pipes (the heat highway)
Two copper pipes connect the indoor unit to the outside unit. One carries refrigerant out, loaded with heat. The other brings it back, ready for more. The bigger pipe is often wrapped in black foam.
Only technicians work on refrigerant pipes.
Stop 9: The outside unit (where the heat goes)
The outside unit holds three big parts:
- The compressor, a strong pump that squeezes the refrigerant so it gets hot.
- The outside coil, which wraps around the sides and lets go of the heat.
- The fan on top, which pulls air through the coil and blows the heat up and away.
Bonus stop: the heating parts
If your home has a heat pump, the same parts run backwards in winter to carry heat inside. If it has a gas furnace, there is a furnace cabinet next to or under the coil, with a burner and a metal heat exchanger. Learn more on How Does a Heater Work?
Parts at a glance
| Part | Its job | Where it lives | Your job |
|---|---|---|---|
| Thermostat | Tells the machine when to run | Wall inside | Read the number |
| Return vent | Pulls air back to the machine | Hallway, wall or ceiling | Keep it clear |
| Filter | Catches dust and fur | Return grille or indoor unit | Remind a grown-up |
| Blower | Pushes air around | Indoor unit | Listen for the whoosh |
| Indoor coil | Grabs heat from the air | Indoor unit | Nothing to do: it’s hidden |
| Drain line | Carries water away | From indoor unit to outside | Report water in new places |
| Ducts and vents | Carry air to rooms | Attic, with vents in the ceilings | Feel the air come down |
| Copper pipes | Carry refrigerant | Between indoor and outside unit | Leave to technicians |
| Outside unit | Sends heat outdoors | Beside the house | Watch from a window |
Try it: the part-spotter hunt
With a grown-up, walk through your home and tick each part you can see.
Can you say which job each part does?
Next stop on the Air Trail: How Does a Heater Work? Or go back to How Does an Air Conditioner Work? See the full Air Trail. Hard words? See Hero Words.
