Last updated on March 10th, 2024 at 03:17 pm

Fixing your window air conditioner instead of replacing it saves you money, hundreds possibly. Chances are, a rattling or noisy air conditioner unit is due to faulty installation, a loose part, loose or worn window frame, loose window panes, loose filter (or wrong filter size), fan obstruction, loose front or side panels, or the condenser coil hitting any moving part (such as the fan).

The good news is you can repair all these.

Faulty Installation

We’re all human, and in the course of “being” human, we’re going to mess up installing something. I’ve done. Everyone’s done it at some point. Typically, a rattling window or window air conditioner unit means the unit isn’t sitting right on the window sill or frame. On most air conditioners, there is a notch, or series of notches that are extra wide and designed to work with most sills and windows – even older ones. The manufacturer also places extra padding, foam, insulation, and support around these areas. The reason is because these areas are in contact with the most solid wood, or frame, and thus most of the weight of the unit is placed in that area, or distributed there.

So, if the unit isn’t sitting right, the moving parts (fan) and heavy pieces that generate noise (compressor) no longer have the cushion, or support. Thus the unit or entire window will vibrate or rattle.

To fix this, look to make sure you are installing the unit correctly. And use the provided screws to fasten the unit to the window, because this will further brace the window and window unit.

Loose parts

Modern air conditioners have moving parts. Fans and compressors are a few of the more noticeable things that can go wrong and “rattle” if they become loose. The simple fix is to simply reattach the broken or loose part. This might require glue, pliers, maybe a screwdriver. In other words, you can do it. The most common repair is the fan being loose here.

Bad frame/window panes

If the installation is correct and all the parts are in order, you may be dealing with loose or worn window frames or window panes. If this is the case, the repair is still simple, but you need to do a little more detective work to find out what the problem is.

If the glass pane(s) vibrate, the problem is loose window panes. Easy, take some window caulk and secure the window to the frame. You might also need to use glass brackets to keep the window in place.

If the glass/pane is fine, then the problem is probably in the frame. You need to dig further and find where the problem is occurring. When the unit is running, lean against different parts of the frame with your hand, putting some or all your weight behind it. If you feel “give” and the air conditioner stops vibrating, you’ve found at least one place where the pane is loose or has gaps. The gaps, or holes in the frame, are what’s causing the vibration. Fill it with putty, or caulk. You may also choose to take apart part of the frame, fill all the gaps, then replace the moulding.

Loose filter

Most window air conditioners are designed to have removable, washable filters that slide into and out of the unit. Check that the filter is snug in place and there is no give. It should be flush against the filter brackets.

If you had to replace the filter, make sure the filter is the right size and fit appropriately. Take it back to the store if it doesn’t fit – I’m sure they won’t mind! 🙂

Fan Obstruction

Most often, during the off-season or during installation, something either fell into the chamber or a piece of insulation broke off and is now coming in contact with the fan when the unit is on. Simple fix – remove it. Avoid opening the unit up, if you can, by taking a pair of tweezers and trying to pull the rogue object out.

Loose Panels

If you’ve ever had to open the unit, or perhaps have to remove the front portion to access the filter, chances are you’ve replaced the panels tightly. But, just to be sure, take a screwdriver to them. Or, try removing and replacing them again. If a bracket or hole was missed (especially plastic notches) the misplaced notch will rattle against the unit and vibrate.

Condenser coil hitting a moving part

This is a tough one, because it could mean any number of things. Although there isn’t much room in a window air conditioner unit, the coil is purposely kept away from the fan or other moving parts. Again, if during moving or installation the coil was dislodged, or disturbed, it might be a little more free to “roam” and come in contact (even slight contact) with the fan. When this happens, the sound is more of a small tiny thumping noise than a rattle. Check the standoffs and replace them, if needed.

Also, if the condenser coil is loose, it might be vibrating on its own and hitting the side panels or housing. The fix is the same – make sure the coil is secure and in its proper place.

What about central A/C units? What can I do there if I hear a rattling?

There’s less user-serviceable features about a central air conditioner. Actually, the window unit doesn’t strictly have user serviceable features either, but the assembly is easier to get to. The number one problem with noises coming from a central air conditioner is due to debris in the unit. Leaves, sticks, twigs, branches, dirt, stones, roofing tiles, screws, nails, tools…you name it, somehow ends up in the unit (at the top) and coming in contact with the fan. This causes the noise.

The solution: Remove the obstruction or debris. The fan assembly is the easiest poertion to get to on central air conditioners. If you can’t pull the obstruction out with tweezers or pliers, turn the unit off completely (so the fan doesn’t turn on when you’re working) and remove the upper housing. Then remove the obstruction.

Aren’t you happy? You just saved a potentially expensive service call.