To replace an in-wall air conditioner, remove the old chassis, inspect or swap the wall sleeve, then slide, level, and seal the new unit.
Swapping a through-the-wall unit isn’t hard if you plan the opening, match the sleeve, and follow safe wiring and sealing habits. This guide walks you from prep to cleanup, with clear steps, sleeves and sizing tips, and fixes for common hiccups. You’ll finish with a quiet, tight install that drains right and cools like it should.
What You’ll Need Before You Start
Before pulling the old unit, stage tools and parts so you’re not scrambling later. The first table lists a full kit and why each item matters. Pick the exact fasteners and sealants that match your wall sleeve and siding type.
| Item | Purpose | Notes |
|---|---|---|
| Tape Measure & Level | Confirm sleeve size and keep the unit true | Level side-to-side; slight outward pitch for drainage |
| Drill/Driver & Bits | Remove sleeve screws; set new fasteners | Have wood and masonry bits if your wall is brick |
| Stud Finder & Pry Bar | Locate framing; remove trim cleanly | Protect paint with a thin putty knife under the bar |
| Utility Knife & Oscillating Saw | Cut caulk; trim shims; open drywall neatly | New blades make cleaner cuts and fewer scuffs |
| Shims (Composite Or Cedar) | Support and fine-tune sleeve position | Composite won’t swell; cedar is easy to trim |
| Backer Rod & Exterior Sealant | Gap control and weather seal | Closed-cell backer rod plus good exterior silicone |
| Flashing Tape | Water management around sleeve | Self-adhesive, compatible with your siding |
| Spray Foam (Low-Expansion) | Air sealing around the sleeve | Low-expansion keeps trim from bowing |
| New Wall Sleeve (If Needed) | Holds the chassis and sets airflow path | Use the brand/model sleeve your unit calls for |
| Safety Gear | Protect eyes, lungs, and hands | Glasses, mask, and gloves for demo and dust |
How The Sleeve And Chassis Work Together
Through-the-wall units ride in a fixed sleeve. That sleeve sets the air path across the outdoor coil, supports the weight, and manages drainage. Many brands sell matched chassis and sleeves; some “universal” sleeves exist, but a misfit can cause noise, rattles, or poor airflow. If your current sleeve is beat up, rusted, or the foam baffles are gone, plan to replace it when you replace the unit.
Energy labels and spec sheets sometimes reference PTAC gear, which also uses sleeves. The idea is the same: a proper sleeve and a chassis that fits it. If your new model calls for a specific sleeve, follow that pairing for a tight, quiet install. For energy performance and placement tips, see the U.S. Energy Saver page on room AC operation and install basics (link the phrase “Room Air Conditioners” directly to the source inside your CMS to open in a new tab).
Safety And Code Basics You Should Know
Room ACs are sealed systems. If you keep the system intact and simply slide out the old chassis and slide in a new one, you’re not opening any refrigerant lines. If you ever need to recover refrigerant or handle a line set, that work goes to a certified tech. The Clean Air Act’s Section 608 rules ban venting refrigerant and require proper recovery gear and certification.
On the electrical side, match the nameplate voltage and amperage. Many in-wall units are 115V with a standard plug; others are 230V with different plug types. A dedicated circuit helps avoid nuisance trips. For outdoor or garage-adjacent outlets, GFCI rules may apply. Local amendments vary, so follow your permit office and a licensed electrician when in doubt.
Read your unit’s manual for exact cord routing, tilt, and mounting hardware. Manufacturers often specify a slight outward pitch for drainage and a level side-to-side stance to prevent gurgle and splashback.
Replacing An In-Wall Air Conditioner: Step-By-Step
This section lays out a clean, repeatable process. The steps assume you’re swapping a like-for-like unit and either keeping a good sleeve or installing the correct new sleeve that the unit calls for.
1) Power Down And Protect The Area
Unplug the unit. If it’s hardwired, switch off the breaker. Lay a drop cloth, pull window treatments back, and tape off nearby trim. Removing a unit can spill some condensate—have a small tray or towels ready.
2) Remove The Old Chassis
Take off the front grille and filter. Look for mounting screws along the bottom rails or side brackets. Support the chassis, back out the screws, and slide the body straight out. Two people make this safer. Set the old chassis on cardboard to avoid scratching floors.
3) Inspect The Existing Sleeve
Shine a light inside the sleeve. Check for rust, bent flanges, broken baffles, and missing insulation blocks. Look outside at the wall cap. If the sleeve is square, solid, and matches the new chassis spec, you can keep it. If not, replace it with the correct model; this protects airflow and keeps the new unit from droning or vibrating.
4) Remove And Replace The Sleeve (If Needed)
Pop interior and exterior trim, cut old caulk, and back out sleeve screws. Ease the sleeve out while a helper supports from outside. If the opening isn’t framed or the old framing is sloppy, box it with 2× framing cut to the sleeve’s rough-open size. Dry-fit the new sleeve with shims. Keep it level left-to-right and pitch it slightly outward so condensate runs outside, not into the wall. Fasten through the sleeve flanges into framing. Flash and seal the exterior perimeter, then foam small interior gaps and reinstall trim.
5) Prep The Opening And Drainage
Clear debris from the sill area. If your sleeve uses drain knockouts or a drain kit, set those now. A clean path and a slight outward angle help prevent gurgling and splash. Many manuals specify a “quarter-bubble” outward pitch on a torpedo level; follow that.
6) Slide In The New Chassis
With a helper, guide the new chassis along the sleeve rails. Don’t force it if it binds; pull out, check alignment, and try again. When the chassis stops at the rear stops, set the locking screws through the provided rails or tabs. Refit the grille and filter.
7) Seal The Gaps And Finish Trim
Seal the interior escutcheon to the wall with a thin bead so air can’t sneak around the unit. Outside, run a neat bead where the sleeve cap meets the siding or brick. Fill larger voids with backer rod first, then sealant. Keep weep paths open.
8) Power Up And Test
Plug the unit in and set it to cool. Listen for rattles, feel for stray air around the trim, and confirm that condensate drips outside. Run it through fan speeds and modes. If you swapped from 115V to 230V or changed plug type, verify the circuit and breaker match the nameplate.
How To Replace An In-Wall Air Conditioner Without Guesswork
The best installs start on paper. Confirm three things before you buy: chassis size, sleeve model, and power. Check the rough opening in your wall and the inside dimensions of the existing sleeve. Then compare those to the manufacturer’s fit chart for the model you want. If the numbers don’t line up, order the matching sleeve and any trim adapters right away.
Cooling capacity should match the room, insulation level, and sun load. Government guides lay out BTU sizing and placement notes. Look at placement tips and capacity adjustments from ENERGY STAR to avoid a unit that short-cycles or never catches up. If the room is a kitchen, you may step up capacity. Corner installs benefit from models that swing airflow to one side.
Can You Reuse The Old Sleeve?
Often, yes. If the old sleeve is the same brand family and size, and it isn’t bent or rusted, you can reuse it. Replace the foam rails, side baffles, and any weatherstrips while you’re there. If the new chassis lists a different sleeve model, don’t try to fudge it. A mismatch can whistle, buzz, or choke airflow. The result is poor cooling and higher power draw.
Electrical Details That Avoid Headaches
Match plug type and circuit. Many 115V units draw under 12 amps; most 230V models draw more and use different NEMA plug shapes. A dedicated circuit reduces nuisance trips when the compressor kicks on. In certain locations, GFCI protection applies to outlets. If your install involves a new receptacle outdoors or near grade, check local rules and the latest code updates with your electrician.
Keep the cord path neat and free of pinch points. Don’t run the cord through the sleeve cavity unless the manual shows a dedicated notch for it. If the unit is hardwired, have a licensed pro make the connection in an approved box with strain relief and the right breaker size for the nameplate amps.
Weatherproofing So The Wall Stays Dry
Water follows the path you give it. Flash the top of the sleeve like a tiny window, shingle-style, so water sheds over the layers—not behind them. On siding, a bead of quality exterior silicone where the sleeve cap meets the cladding keeps wind-driven rain out. Inside, a thin continuous bead around the escutcheon stops hot air from sneaking behind the unit and condensing on cool framing. Leave any weep holes clear so the pan can drain outdoors.
Noise, Vibration, And Rattle Control
Most noise comes from three spots: a sleeve that’s out of square, loose mounting screws, or missing foam rails and baffles. Square the sleeve, shim behind the flanges where needed, and snug all fasteners. Reinstall side and top foam rails exactly as the manual shows. If the exterior grille buzzes, add a thin foam shim under the contact points. A slight outward pitch helps keep water from pooling in the pan and gurgling.
Care And Setup After The Swap
Wash or replace the filter after the first week—demo dust can clog it fast. Set the thermostat to a realistic target and use auto-fan for better dehumidification. Keep lamps or TVs away from the thermostat area so the unit doesn’t run longer than it should. If your model has an energy saver or eco cycle, try it once the room is at temp.
Two trusted resources worth saving: the U.S. Department of Energy’s Room Air Conditioners page for placement and operation tips, and the EPA’s page on the prohibition on venting refrigerants if equipment ever needs recovery.
Common Pitfalls When Replacing An In-Wall Unit
Buying By BTU Alone
Capacity matters, but airflow pattern, sleeve fit, and sound ratings matter too. In long rooms or corner installs, a louver that can swing air to the open side makes a bigger difference than one more half-ton of cooling.
Skipping The Sleeve Check
A bent sleeve or crushed baffle will drone. If the old sleeve is dented or the rear cap is missing fins, replace it. The new chassis will thank you with smooth airflow and less compressor strain.
Forgetting The Outward Pitch
Flat installs can hold water in the pan, which gurgles and can splash indoors on windy nights. Keep the sleeve level side-to-side, then pitch the chassis slightly outward.
Using The Wrong Sealant Or Foam
High-expansion foam can bow trim. Choose a low-expansion type and use backer rod for gaps bigger than a pencil.
Quick Checks After You Power On
- Feel for stray air around the interior trim. Add a small bead where you find leaks.
- Listen for rattles. A half-turn on a rail screw often fixes it.
- Look outside for steady drips in cooling mode. No drip can mean the pitch is wrong or the pan is blocked.
- Run fan speeds and swing louvers to confirm smooth travel.
Size, Sleeve, And Power: A Mini Match Guide
Use this quick reference to confirm that the model you’re eyeing will actually live happily in your wall. When in doubt, buy the correct sleeve the manufacturer lists.
| Check | What To Verify | Why It Matters |
|---|---|---|
| Chassis Size | Height, width, depth vs. sleeve interior | Stops rattle, air bypass, and binding |
| Sleeve Model | Exact model number match or approved adapter | Preserves airflow path and service clearances |
| Voltage/Amps | Nameplate vs. receptacle and breaker | Prevents trips and meets listing |
| Drain Setup | Outward pitch and any drain kit installed | Keeps water outside the wall |
| Filter Access | Front grille clears trim and curtains | Makes monthly cleaning easy |
| Air Throw | Louver swing reaches the room’s long side | Even temps without dead zones |
| Noise Rating | DbA spec at typical fan speed | Comfort at night in bedrooms |
Frequently Asked Questions You’ll Ask Yourself Mid-Install
“My Old Unit Was 115V, The New One Is 230V—Now What?”
You’ll need a matching receptacle, correct breaker size, and the right wire gauge. If you don’t already have that circuit, stop and call an electrician. Don’t adapt plugs or run long cords.
“The New Chassis Stops Short In The Sleeve—Is That Normal?”
Many models slide until the rear gasket contacts the sleeve cap, then lock with side screws. If it feels wrong, pull out, check for warped rails or loose packaging foam, and try again. Never force it.
“Can I Tilt The Unit A Lot To Get More Drip Outside?”
No. Too much pitch can starve the indoor coil pan and raise noise. Keep it level side-to-side and just a slight outward tilt. Follow the manual for the exact target.
Maintenance That Keeps Cooling Strong
Clean the filter monthly in heavy use. Vacuum the indoor coil face with a soft brush when the grille is off. Outside, clear leaves from the rear grille twice a season. Re-caulk tiny gaps that open with seasonal movement. These quick jobs keep airflow high and energy use low.
When To Call A Pro
Bring in a licensed tech if the unit ices over, trips the breaker at startup, or shows error codes tied to sensors or thermistors. Any work that opens the refrigerant circuit belongs to a Section 608-certified technician. If you’re changing from 115V to 230V power or moving the opening to a new spot in the wall, a permit and electrician save time and prevent callbacks.
Your Clean, Quiet Finish
You now know how to replace an in-wall air conditioner the right way: match the sleeve, frame square, pitch for drainage, seal smart, and test for leaks and rattles. With a careful prep list and steady steps, the swap is a tidy weekend project that rewards you with better comfort and lower noise.