How to Install Window Air Conditioner Side Panels | No Drafts, No Gaps

Installing window AC side panels requires sliding the accordion panels into the unit’s side rails, extending them to meet the window frame, and securing them with screws through pilot holes to create a weathertight seal.

Nothing kills a room’s cool air faster than gaps around a window AC unit. The side panels — those accordion-style curtains — are what stop hot outdoor air from leaking back in. They also keep the unit stable and prevent bugs from marching through. Here is the exact sequence for getting them right the first time, whether you are using a GE, Frigidaire, or any standard double-hung window unit.

What You Need Before You Start

Gather these items before lifting anything: a drill with a 1/8-inch bit, a Phillips screwdriver, weather stripping (often included with the unit), and a second person — these units are heavy, and dropping one can damage the frame or the AC itself. The hardware bag typically contains two types of screws: Type-A screws for the top mounting rail and Type-B screws for the side panels.

Step-by-Step Side Panel Installation for Double-Hung Windows

These steps assume a standard vertical sliding (double-hung) window. Horizontal sliders require different parts — we cover that below.

1. Slide the side curtain panels into the rails on each side of the AC unit. The frames are marked Left and Right — match them correctly or the panels will not extend properly.

2. Extend the panels outward until they press against the window sash tracks on both sides. The panels should fill the gap evenly without buckling.

3. Drill 1/8-inch pilot holes through the screw holes in the side panels into the window sash or frame. Skip this step and you risk splitting the wood or stripping the screws. Use the Type-B screws to secure each panel — four per side.

4. Apply weather stripping to the top and bottom edges of the window sash and along each side of the curtain frame. If the unit includes adhesive-backed foam sheets, measure them against the curtain panels, cut to fit, and press them into place. This seals the small gaps the panels themselves cannot cover.

5. Close the window onto the top of the AC unit’s box, making sure the upper sash sits behind the unit’s upper flange. This locks the unit in place vertically.

6. Install the L-shaped security brackets — usually included — to the upper window sash to prevent anyone from pushing the window open from outside. Some units also accept a screw through the upper flange directly into the sash for extra peace of mind.

7. Check the tilt: the unit should sit level or slope slightly downward toward the outside so condensation drains properly. Read the manufacturer’s instructions on drainage — some units have a specific tilt requirement.

Common Mistakes That Wreck the Seal

Three errors show up in most failed installations. First, people skip the pilot holes and either snap the screws or cannot get them to bite. Second, they install the weather strip after the unit is fully screwed in, leaving tiny gaps they cannot reach. Measure the window center first, align the unit to it, then extend the panels evenly.

If this is your first install, browse top-rated side panel options that fit mismatched window widths — some universal panels save you from buying a whole new AC.

What Changes for Horizontal Sliding Windows

Double-hung instructions do not apply directly to horizontal sliders. For these windows, you generally need aluminum angle pieces, plexiglass panels, or custom spacer blocks to bridge the gap above the unit (since the side panels are designed for vertical gaps). Measure the height of the open window space and cut a filler panel that fits snugly. Attach it with brackets or through-frame screws. Also check for storm window frames that might block the AC’s chassis from sitting flush.

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