air conditioner air filter

Dirty air filters are the main reason air conditioners don’t work as well as they should. Every time the air conditioner runs, it pulls air through its filter. The purpose of the filter is to catch impurities in the air. With those particles stuck to the filter, the path for air gets blocked to a greater and greater degree, meaning there’s less air through the air conditioner and thus less cooling. It also means the air conditioner works harder and uses more power.

Filters should be changed every 30 to 60 days that the air conditioner runs, say most manufacturers, but this a very rough estimate since individual homes and offices vary. Why don’t people change the filter? Partly laziness, partly since air conditioners aren’t exactly top of mind projects, and partly because simply don’t realize how dirty their air is.

It used to be that you could just look through a filter and if you could see light through it, it didn’t have to be changed. Some of the filters supplied with air conditioners still work that way, but you have a lot more options in picking your filter. The standard piece of flimsy foam only catches large objects, and functions far more to protect the insides of the air conditioner than your health and your air.

So if you’re going to change the filter the first question is: are you supposed to? There are some filters that are made to last as long as the appliance, or several years at least. Those filters should be cleaned, not replaced, although if you want better filtering you can still replace them.

There are many choices that will do a better job of filtering than a simple piece of foam. There are filters that remove very small particles from the air, filters designed to combat allergens, filters designed to hold particles in the filter media for a longer time, filters designed to cut down on smoke, and several other variants. They may be made of foam, paper, charcoal, electrostatically charged foam and a few other materials. Some makers stress the strength and integrity of the frame that holds the filter, if there is one.

A check of what’s available on the web or in the catalogs will explain a lot of what these filters do, but since you’re going to have some kind of filter in the system getting one that meets your particular situation makes sense. The basic compromise all filter makers run into is that the better a filter is at removing particles from the air, the more it will impede air flow, and a lot of technology has gone into trying to change that to the degree possible.

Filters are rated in terms of “Arrestance”, a figure of merit that refers to how much synthetic dust the filter removed from the air in a standardized tests. Filters typically will remove 85 to 95 per cent of the test dust.

Filters are also rated in terms of resistance to the air flow. This is expressed in the U.S. in “inches w.g.” where w.g. stands for “water gauge”; the rest of the world uses Pascals of pressure. A filter might have a resistance of .07 to .20 inches initially. A manufacturer will say the filter should be cleaned or replaced when it reaches .4 or .9. While it’s not possible to measure this without equipment such as a water gauge, it should give you an idea of how much the filter’s resistance can increase after a month or two.

There are other filter qualities that manufacturers can explain in great detail. Always refer to the air conditioner’s manufacturer’s recommendations on acceptable filters, either by type or by the amount of resistance that’s acceptable. The air conditioner manufacturer has also specified a certain size for the replacement filter, which must be followed, although measuring the old filter works, if that filter was correctly sized.

Filters are simply specified by the height and width, plus the thickness. Sometimes a thicker filter than originally supplied will fit, and if it does can provide better filtering. Filter dealers will generally have the ability to build a filter in a custom size if your unit needs a non standard size.

Once you’ve made a choice of filters, the procedure is very simple. First shut off the air conditioner. It doesn’t hurt to pull the plug or shut off the breaker either.

To remove the filter you have to find it. The filter is always behind the grill that takes in room air.

The air conditioner will have the filter behind a door that must be opened, in a slot where it can slide out, or behind a panel that holds the grill that gets pulled out toward you. This is always described in the maker’s instructions. Don’t force anything, but you should be able to figure out what comes off. If you can’t a quick call or email to the manufacturer or local dealer – “How do I get to the filter?” should get you the answer.

Once the filter’s exposed, study it to see how it attaches, either with clips or an elastic band across it. You’ll have to replace the filter by putting everything back. The elastic, if used, may be deteriorated and a new one should be available from the dealer.

It’s a good idea to remove the filter from the holder outdoors since some dust is apt to fly around. Remove the filter and pop it into a plastic bag for disposal. If it’s washable and you’re going to clean it, follow the maker’s instructions if you have them, otherwise vacuum off the loose dirt, then wash the filter with warm water and small amount of dish detergent, then rinse with plain water.

Vacuum off the grill at this point, too. If you see that the fins and coils on the air conditioner are dirty, you can vacuum them off, too, and if it’s a window unit you can pull the power cord and slide the thing out of its sleeve and vacuum the whole works, being careful not to dislodge any of the mechanical parts. Or call a technician if you want. Air conditioners are supposed to be serviced every few years.

Take your new filter, make sure that if it specifies a direction for the air flow you have it oriented that way, pop it into its holder and put the retaining system back the way it was, then put the assembly back into the air conditioner.
Put the power back on and you should be all done once you mark your calendar to repeat the process next month.

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