Mark’s Seasonal Game Plan: Prepping Your Through-the-Wall AC for Winter and Beyond

🧊 From Mark’s Workshop to Your Home

Hey folks, Mark here! 👋

If you’ve been following along with my series on through-the-wall ACs, you know I’m all about keeping your system running smooth and efficient. But there’s one piece that gets overlooked all too often — winter care.

Let me tell you, ignoring your through-the-wall AC when the weather turns cold is like leaving your car out in a blizzard with no antifreeze. Over time, moisture, debris, and freezing temps can sneak in and cause rust, leaks, or damaged seals. That can mean a costly repair or even early replacement when you flip that switch next summer.

So in this article, I’m going to walk you through the full seasonal prep playbook — exactly what to do when the cooling season winds down, how to protect your unit through winter, and how to get it ready to crush next summer’s heat.

Here’s what we’ll cover:
✅ Cleaning and maintenance checklist before winter
✅ How to protect your unit from snow, ice, and drafts
✅ Seal-up techniques to keep out pests and moisture
✅ Tips for spring startup after a long winter nap
✅ Common winter-related problems and how to avoid them

And yes — I’ll toss in some solid, trusted resources along the way, so you’ve got expert backup to lean on.

Ready to protect your investment and keep your home comfy year after year? Let’s get into it! ❄️🧰

 

🍂 1️⃣ The End-of-Season Deep Clean

The first step to winter-proofing your through-the-wall AC is to give it a thorough clean as you shut it down for the season.

Here’s the checklist:

• Turn off and unplug your unit. Safety first, always.

• Remove and clean the air filter. Wash it with warm soapy water or replace it if it’s disposable.

• Clean the coils and fins. Use a coil brush or soft cloth to remove dust and grime. A dirty coil invites mold and reduces efficiency.

• Vacuum the inside and the drain pan. Make sure there’s no standing water left to freeze and cause damage.

• Check the exterior sleeve and frame. Remove leaves, dirt, and debris that may have collected around the unit.

If you want step-by-step visuals and extra tips, check out this Energy Star guide on AC maintenance.

 

❄️ 2️⃣ Seal It Up Tight — Keep Out the Winter Weather

Once your unit is clean and dry, it’s time to block out the winter chill. Moisture and drafts are your biggest enemies.

• Install a weatherproof cover designed for your model. Avoid plastic tarps — they trap moisture and cause rust. Look for breathable fabric covers made specifically for through-the-wall units.

• Use foam insulation or weather stripping around the interior edges of the sleeve to seal gaps and prevent cold drafts from sneaking in.

• Check and repair exterior caulking and seals. Any cracks let water and pests inside. Use a good quality, exterior-rated caulk for patching.

• Add a vent blocker or foam plug for the vent if your model allows it — this stops drafts and critters from nesting in the winter.

For sealing tips that go beyond the basics, the This Old House winterizing guide has some great insights.

 

🌨️ 3️⃣ Snow, Ice & Drainage: What to Watch For

Snow and ice can pile up around your through-the-wall AC’s exterior sleeve. If it melts and refreezes, it can block drainage and cause water backup inside your home.

• Clear snow and ice regularly from around the unit. Use a soft broom or brush to avoid damaging the grille.

• Make sure the unit is tilted slightly downward outside so water flows out and away from your home.

• Check the drain line for clogs and blow it out before the freeze hits to avoid ice blockages.

• If your area gets heavy snowfall, consider installing a small protective awning over the outside sleeve for added shield.

For detailed advice on managing winter weather around your AC, check the U.S. Department of Energy’s seasonal maintenance tips.

 

🧹 4️⃣ Pest Prevention — Keep the Critters Out

Winter is prime time for mice, spiders, and insects looking for a warm nook to call home — and your through-the-wall AC sleeve is prime real estate.

• Seal all gaps and cracks around the sleeve. Use steel wool or wire mesh plugs for bigger holes, then caulk over them.

• Install a vent cover with a fine mesh screen to block bugs without blocking airflow in summer.

• Regularly inspect for signs of nests or droppings. Remove them promptly.

If you’re dealing with persistent pests, you might want to check out some non-toxic pest control tips from The Humane Society’s pest prevention guide.

 

🌱 5️⃣ Spring Startup: Getting Ready for Action

Come spring, your AC needs a smooth restart after hibernation. Here’s your startup checklist:

• Remove the winter cover and inspect the unit. Check for any damage or rust.

• Clean or replace the air filter.

• Inspect the coils and fins — clean if necessary.

• Test the electrical connections (or have a pro do it).

• Turn the unit on for a short test run. Listen for odd noises, and check airflow and temperature.

If you want a detailed walk-through, the Family Handyman spring AC checklist is solid.

 

⚠️ 6️⃣ Common Winter Problems & How to Avoid Them

Here are some headaches you want to dodge:

• Water leaking inside from clogged drain lines — clean the drain before winter and check seals.

• Mold and mildew growth on coils — clean coils and keep the unit dry before storing.

• Rust from trapped moisture — avoid plastic covers; use breathable fabric covers.

• Pests nesting inside the sleeve — seal gaps and install mesh guards.

• Cracked or damaged seals causing drafts and inefficiency — inspect seals yearly and recaulk as needed.

 

🧊 Mark’s Closing Tips

Alright — that’s your full winter armor for your through-the-wall AC. Treat your unit like the hardworking home hero it is, and it’ll reward you with years of cool, comfy air when the heat rolls back around.

Winter prep is not just about shutting down — it’s about protecting, sealing, and inspecting so your AC can bounce back strong every spring. A little effort now saves you costly repairs later.

If you’re looking to shop or upgrade your through-the-wall AC before next season, check out the full lineup at The Furnace Outlet’s through-the-wall collection. They’ve got reliable models, and you can pair your pick with the seasonal care tips we covered here.

Curious about wall sleeves for your wall AC? Visit my guide: Replacing a Through-the-Wall AC Sleeve the Right Way.

Thanks for sticking with me on this journey — here’s to many more years of cool comfort, no matter the weather. Stay warm this winter, and stay tuned for more tips to keep your home running smooth year-round. ❄️💪

— Mark OUT!