How to Winterize Your AC Unit Posted on October 4, 2024 It’s deep winter. The house is fully sealed and insulated, thermostat up high. As everyone settles around the warm glow of the fireplace, you may have forgotten one thing: your poor air conditioner. As the snow thaws and spring arrives, you fire up the old AC unit only to find it dead. It turns out the poor AC frozen solid outside, covered in ice and debris, leading to expensive repairs or replacement. This is a common scenario for homeowners who fail to properly winterize their air conditioners. Without adequate preparation, air conditioners can be vulnerable to the harsh winter elements, which can cause damage to its components and significantly shorten its lifespan. In this guide, we walk through the essential steps to winterize your AC, prevent unnecessary damage, and prolong its lifespan in harsh winter conditions. Should I Cover My AC Unit in the Winter? A common question many homeowners ask is whether they should cover their air conditioning units in winter. The answer depends on the type of AC unit you have and the local climate, but in general: Window air conditioners: If possible, it is best to remove the unit from the window in the winter, but if you cannot, covering the outdoor compressor is essential to protect it from snow and ice. It also protects against cold drafts that can enter your home through gaps in the seal. Use a cover specifically designed for window ACs to ensure proper insulation without sealing in moisture. PTACs: Packaged terminal air conditioners (PTACs) are generally used in commercial settings, but they can also be found in residential applications. PTACs almost always provide heating in addition to cooling. If you are using the heating function, you cannot cover the unit. In fact, you should make sure the back of the unit is free of snow and ice so it does not impede airflow. Mini-splits: Many mini splits are also heat pumps. Mini-split systems have outdoor condenser units that need to be protected from snow and debris. While a full cover is generally not recommended, using a top cover to shield the fan and components from debris can help maintain its performance. For heat pump mini splits, a stand can also be useful to keep the unit out of the snow. Through the wall ACs: If your through-the-wall unit has a built-in heat pump or an electric heat strip, covering it could hinder its performance if you use the heating. Otherwise, it’s recommended to cover a through the wall AC to protect against snow. Central AC: Central air conditioners are built to withstand outdoor conditions year-round. Most are designed to handle rain and snow, so a cover isn’t strictly necessary. However, if your area experiences extreme winter conditions, covering the outdoor unit could help protect it from snow, ice, and falling debris. Some homeowners opt to cover only the top of the unit, using plywood similar shielding to protect the top from falling debris, while leaving the sides open for airflow. This prevents moisture buildup while offering some degree of debris protection. Possible Consequences of Not Winterizing Your AC Unit Failing to properly winterize your air conditioner can lead to various issues, such as: Freezing and cracking Moisture inside the AC unit can freeze during cold temperatures, causing components such as coils and pipes to crack or rupture, leading to refrigerant leaks or total unit failure. Rust and corrosion Exposing your AC unit to moisture and snow without proper protection can lead to rust and corrosion of metal parts. Once corrosion sets in, it can affect the structural integrity and function of the unit. Debris buildup Over the winter, debris like leaves, branches, and dirt can accumulate inside the unit, clogging vital parts like the fan and condenser. This can cause the unit to work harder and reduce efficiency when it’s in use again. Animal intrusion Small animals such as rodents or birds may seek shelter inside uncovered units, causing damage to wiring and other components. Inefficient operation For window and PTAC units, not sealing the unit properly can cause drafts, leading to higher heating costs in winter. When Should You Not Use the AC in Winter? If your air conditioning unit includes a heat pump feature, it can provide supplemental heating in winter, but there are temperature limits to be mindful of: Below 40°F (4°C): In most cases, you should not operate a standard AC unit when outdoor temperatures fall below 40°F. Many air conditioners are not designed to run efficiently in colder temperatures, and doing so can cause the unit to freeze up or suffer damage. Heat Pumps: While heat pumps are designed to work in colder conditions, most systems struggle to function efficiently when temperatures drop below freezing (32°F/0°C). At extremely low temperatures, a heat pump may enter Defrost mode to prevent ice buildup on the coils, but in extremely cold regions, it’s best to have a backup heating system. In subfreezing conditions: Using the AC in subfreezing temperatures could lead to compressor failure and damage to internal components. If you rely on the heat pump function, consult the manufacturer’s manual for recommended operating temperature ranges and ensure the unit has freeze protection features. How Do You Protect an Air Conditioner in the Winter? To prevent damage and extend the life of your AC unit, follow these comprehensive winterization tips for different types of air conditioners: Window AC Units ☑ Use a Proper Cover: Cover the outside part of the unit with an insulated cover. Ensure the sides are sealed to prevent drafts but allow some ventilation to prevent moisture buildup. ☑ Seal the Window: Use weather stripping or foam insulation around the edges of the window to prevent cold air from seeping in. Check out our detailed guide to Window Insulation. Mini-Splits ☑ Inspect and Clean: Remove any debris from around the outdoor unit and clean the condenser coils. Make sure there’s adequate airflow around the unit. ☑ Install a Top Cover: Use a mini-split condenser cover that shields the top from snow and debris, but leave the sides open for proper airflow. ☑ Clear the Area: Ensure the area around the outdoor unit is clear of snow, ice, and debris. If you expect heavy snowfall, create a barrier or shelter to keep the unit free from obstructions. Here’s our complete guide to Mini Split Cleaning and Maintenance. PTACs ☑ Clean Filters and Coils: Regularly clean the air filters and evaporator coils to ensure efficiency. ☑ Check Seals and Gaps: Make sure there are no gaps around the PTAC unit that could let in drafts. Insulate or seal any gaps properly. ☑ Install a Winter Cover: Use a winter grille cover or weatherproof panel to protect the exterior part of the PTAC unit from snow and moisture. Also check out our PTAC Troubleshooting Guide in case of any issues. Through the Wall ACs ☑ Clean Coils and Fins: Use a soft brush or vacuum to clean the evaporator and condenser coils. Also wipe or vacuum the fins of any dust, dirt, or debris. ☑ Clear Drainage: Ensure drainage holes are clear to prevent any water from accumulating inside the unit, which can freeze and damage components during the winter. ☑ Get a Weatherproof Cover: Purchase a high-quality cover specifically designed for through-the-wall AC units. These covers have built-in vents to allow moisture to escape while still protecting the unit from external elements. Look for one made from waterproof and weather-resistant materials like vinyl or heavy-duty polyester. This will protect the outside part of the unit from snow, rain, and debris. ☑ Install Insulating Foam: You can place insulating foam around the perimeter of the unit, between the unit and the wall, to create a tighter seal. This lessens drafts and minimizes heat loss. Central AC ☑ Clean the Coils: Spray the coils with a hose to remove any dirt or dust buildup. If needed, use a coil cleaner that’s safe for AC units. We carry condenser cleaners from trusted brands, as well as applicators. ☑ Check Drainage Lines: Make sure there is no standing water in the drain pan, and clear any blockages from the drainage lines to prevent freezing. ☑ Inspect Refrigerant Lines: Check the refrigerant lines (usually copper pipes covered with insulation foam) for any signs of wear or damage. Also keep an eye out for any refrigerant leaks, which will require a top-up by an HVAC professional. ☑ Add or Replace Insulation: If the insulation around the pipes is damaged or missing, replace it with foam insulation to protect the lines from freezing during winter. ☑ Check Drainage Path: Make sure the area around the outdoor unit is graded properly so water doesn’t pool around the condenser. Water buildup can freeze and cause damage to the unit. ☑ Elevate If Needed: If the condenser sits on low ground, consider using a platform or stand to lift it slightly off the ground to prevent water or snow accumulation. Check out our condenser stands to ensure your condenser stays high and dry. ☑ Consider a Cover: Covering your outdoor condenser unit is optional. While some manufacturers advise against it because the unit is designed to withstand winter conditions, covering it can help keep debris and moisture out. If you do choose to cover it: Use a breathable, waterproof cover that allows air circulation. Avoid fully sealing the unit, which can trap moisture and cause rust or mold growth. (Optional) Cover only the top. Some homeowners prefer using a top-only cover or plywood to prevent leaves, snow, and ice from entering while still allowing airflow to the sides. ☑ Switch to “Heat” Mode: If your central AC is part of an HVAC system that also provides heating, make sure the system is switched to the heating mode on your thermostat. This prevents the AC from accidentally running in winter. Portable ACs ☑ Drain All Water: Before storing your portable AC, drain all water from the condensate tank. Portable units typically collect water when dehumidifying the air, and any remaining water can freeze and cause damage. Remove the drain plug and allow the unit to completely empty. If your model has a continuous drain feature, make sure the hose is also clear of any water. ☑ Clean the Unit: Clean or replace the air filters to remove dust and debris. Clogged filters can harbor mold or bacteria, leading to poor air quality when the unit is used again. ☑ Run on Fan Mode: After draining the water, run the unit on fan mode for a few hours to ensure all internal components are thoroughly dry. This step helps remove any lingering moisture that could cause mold growth or freezing damage. ☑ Avoid Storing Outdoors: Always store your portable AC indoors during the winter. Storing it in a garage, basement, or storage closet is ideal. Make sure the storage area is dry and protected from extreme cold or humidity. ☑ Cover: If you plan to store the unit for several months, use a cover or a tarp to protect it from dust accumulation. Make sure the cover is breathable to avoid trapping moisture inside. Winterizing your air conditioner is crucial to maintain its longevity and ensure optimal performance come spring. Whether you have a window AC, PTAC, or mini-split, taking the time to protect your unit from winter’s harsh conditions will save you from higher utilities and costly repairs. Also check out our other winter topics: How to Winterize your House: A 20-Point Checklist The Weakest Link: Attic Sealing and Insulation Before Winter Mickey Luongo Mickey is the resident heating and air conditioning expert with over 15 years of experience in the industry.