Window air conditioners:
This article helps choose, install, maintain & troubleshoot window and through-wall air conditioners. We include s to additional details about window and through-wall cooling unit capacity, safety supports, filters, compressor/condenser troubleshooting, dirt and mold cleanup, and other issues.
We describe the simple process of installing or removing a window air conditioner, how the unit should be stored when not in use, and we explain what to do if the air conditioner condensate is not going where you want it to.
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Window air conditioner size or capacity
For help choosing a window or through-wall air conditioner of the right size or capacity, see AIR CONDITIONER BTU CHART.
Typical Window Air Conditioner Installation
As we discuss also at WINDOW / WALL A/C SUPPORTS, at below left the accordion-type expanding window-mounted air conditioner opening bracket upper edge, braced against the lower edge of the window sash, is the principal connection that keeps this unit from falling out of the window opening.
Watch out: both during window air conditioner installation and more so when you are removing the unit at the end of the cooling season, simply raising the window sash can result in the whole assembly falling off of the building.
Short screws, often sheet metal screws secure the expanding bracket and window-filler on the sides of the air conditioner to the window sash bottom edge near the left and right ends of the upper sliding metal bracket. And two additional screws secure the accordion expanding fillers to the trim on either side of the window frame.
These little screws are not structural and do not provide much additional security against losing the whole air conditioner out the window. The outside view of this type of window air conditioner makes clear that it has no other support.
Watch out: inadequately-supported outdoor window air conditioners or inadequately-supported wall-mounted outdoor compressor/condenser units (referred to as the "inverter unit" in some literature) pose a potentially fatal hazard should one of these units fall from the building onto someone below.
In 2012 the New York Times reported that that city has increased enforcement of proper exterior supports for air conditioners at public housing after air conditioning units fell out of two windows in a housing project on the upper East Side of New York City.
In 1988 a pedestrian was killed when an air conditioner fell from the seventh floor of a building in New York. 
While those air conditioner falls, one onto a playground near children, luckily didn't hurt anyone a falling A/C unit (window air conditioners) or compressor/condenser unit (split system air conditioners with an outside wall-mounted compressor unit) are very dangerous.
Details about the support requirements for window and through wall air conditioners are at WINDOW / WALL A/C SUPPORTS
Proper Methods for Removing & Storing a Window Air Conditioner
Heavy through-window air conditioners and most through-wall air conditioners are left in place year round. But because of possible air drafts and heat losses through the equipment during cold windy weather, many owners either cover those units or for smaller window air conditioners such as the unit shown just above, the unit is removed and stored.
When a window air conditioner unit is to be removed and stored at the end of the cooling season
Watch out: if you store a window or through-wall air conditioner in any other position there is risk that refrigerant and oil will move into and clog the capillary tube that meters refrigerant. If you turn on an air conditioner where this mistake was made, on some window air conditioners the unit won't work - the motor may run but it won't produce cool air. Usually you can "fix" this mistake by simply leaving the unit in its proper position for 24 hours, giving oil time to flow back out of the refrigerant line and cap tube.
Window air conditioner condensate disposal
Thanks to reader Brian B for suggesting this material.
Question: how to route condensate from a window air conditioner
Brian: about window A/C unit condensate drip pans and condensate disposal troubles:
The drip pan includes a condensate drain port that either drips directly out of the bottom back of the unit, usually at a corner, or the port, a small metal tube, can be connected to a drain hose to route condensate to an acceptable location so that it does not drip, for example, on the head of someone walking below.
That's a particular problem when the A/C unit is installed over a door as we often see at business entrances.
Watch out: in some municipalities it is not permitted to drain A/C condensate across a sidewalk - in such cases the property owner has to route condensate to a floor drain or similar location. When there is no drain close by that can be reached by gravity, you can still solve this problem easily by having the A/C condensate routed to a small condensate pump that then pumps condensate to an acceptable drain location.
Clean the air conditioner filters monthly during the cooling season. This is the single most important step you can take to keep your unit working effectively.
On some units (left) the air conditioner filter slides up or down for removal and washing.
On other window or room air conditioners you have to un clip and remove the entire front cover to access, remove, and clean the air filter.
If the air filter is a sheet of foam that is torn or disintegrating, just replace it. You can usually find replacement window air conditioner filter materials at building supply stores.
The new filter may have to be trimmed to fit.
Also check the cleanliness of the the unit cover itself.
Both the air intake and air supply louvers can become thick with dust - blocking air flow as well as possibly adding to airborne dust and debris as well as speeding clogging of the unit's air filter.
When we see an air conditioner as dirty as this one (photo at left) we figure it has had little maintenance or attention and that it needs cleaning.
On some room or window air conditioners it's easy to know if the air filter needs washing or replacement.
Some units actually provide a signal: a light or a red indicator showing that the air filter is blocked, air flow is reduced, cooling capacity is reduced, and the unit needs cleaning.
On other units such as the photo at left, just peeking through the air inlet openings you can see if the filter surface has become thick and clogged with dust and debris.
The window unit air conditioner air filter in our photo needs to be cleaned or replaced.
When you have completed your air conditioner and filter cleanup, make sure that the room or window air conditioner front cover is properly and squarely mounted and secured.
If the cover is loose you may be annoyed by rattles and noises coming from the unit.
The room air conditioner shown at left is an older unit whose controls are behind an openable panel at the left side of the unit.
You can see that the unit cover is askew (upper right corner) and is not properly secured.
On one of our older air conditioners the springs that held the cover in place were lost. An expedient that was ugly but worked fine was simply to use some duct tape to secure the plastic cover to the air conditioner frame. The tape has to be peeled away and replaced each time the cover is removed to access and clean the air filter.
If you see mold growth on or inside the air conditioning unit you may want to turn it off, remove and wash the plastic cover fittings and parts, and working gently so as not to bend or break anything, manually clean the accessible portions of the blower fan and air passages.
Take care not to bend or damage the cooling coil fins.
Any household cleaner, spray diluted bleach, etc. can be used to clean these plastic surfaces.
Cleaning Procedures for Dirty window air conditioner or room air conditioner cooling coils
Our photo (left) shows what happens if you operate a window or room air conditioner with no air filter installed. The cooling coil fins become blocked and clogged with dust and crud.
This reduction in air flow cuts the cool air output of the air conditioner and can eventually lead to complete loss of function as the unit can also begin to ice-up.
There are several approaches to cleaning up a mess like this - all of them should be followed with care not to bend or damage the cooling coil fins as doing so reduces air flow through the air conditioner. Some options include:
Window or Through Wall Air Conditioner Operating Problems
If the air conditioner will start and run, and air blows out of the supply register but it never cools, make sure that the thermostat is set all the way to the coldest position. If the unit still won't produce cool air it needs service or repair. The unit may have lost its refrigerant charge.
But before calling your service technician, if you have just installed the air conditioner, and if it is new, or if it was working when last removed, you may have stored it in an improper position, allowing refrigerant oil to block a refrigerant metering device or capillary tube. Try leaving the unit off but in proper operating position for 24 hours, then try turning it on again.
If you don't have the installation, operation, and maintenance guide for your window or room air conditioner, check the model and serial number (see our photo at above left) and then contact your unit's manufacturer.
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