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What kind of air conditioner do you have?

What kind of air conditioner do you have?

An air conditioning system is certainly not the most interesting equipment that you choose for your home, or that comes with an existing home you buy.  It either works well, or it doesn’t, right?  Unfortunately it’s the ones that don’t work well that get noticed!  Depending on the size of home, configuration and budget, there are about 7 different types that may be used.  Here’s how to tell what kind of unit you have, and what kind you may want to upgrade to in the future!

Before talking about all the different types, however, let’s go over the basic parts of an air conditioner by looking at one of the most compact and common versions, a window air conditioner. 

(diagram source: studentlesson.com)

The components of a window air conditioner can be found in most other systems.  To start, note that the outside air and the inside air don’t mix.  Indoor air stays inside and outdoor air stays outside; it’s the refrigerant in the coils that goes back and forth, transferring heat from indoor air to the outside air.  Let’s start with warm indoor air.  In this diagram, it’s sucked into the unit from the right (“Indoor Air” red line), via a squirrel-cage blower (circular cage), and blown over the cooling coils (blue line going back and forth), making the air cool.  The air is blown out the front of the unit and voila!  The room becomes cooler.  What happened to the heat from the air?  Here it’s useful to show another diagram, which is of the refrigerant system only.  

(diagram source: swtc.edu)

Once you understand this inside/outside, low-pressure/high-pressure system, you will be able to understand most of the common refrigeration systems!  The heat of the inside air was absorbed by the refrigerant in the cooling coils (see left side of diagram).  The cooling coils are also called the evaporator, because inside the cooling coils, the refrigerant changes from a liquid to a gas (evaporates) with the addition of the heat of the inside air. Once the refrigerant passes all the way through the evaporator, it is drawn outside by the compressor, which changes it from a warm gas to an even hotter gas.  The hot gas will then pass through the condenser, which is another set of coils over which a fan blows outside air.  When heat is drawn from the gas, it turns into a liquid again (upper right side of the diagram).  Before passing to the evaporator again, it must flow through the expansion valve, which is a very important part of the air conditioner.  The expansion valve gets a signal from the temperature sensing bulb (first diagram), and only lets a small portion of the hot pressurized gas into the evaporator as needed, creating a low pressure area on the cooling side.  Then we have completed the cooling cycle, and the refrigerant makes another loop while the fans serve to transfer heat to the air on each side of the window.  

Central Air Conditioning uses all of these basic components, serves multiple rooms in a home, and can be categorized into two types: Split and Package.  The main difference between these two is the location of the evaporator.   In addition, central air conditioning can be used for heating if it uses a heat pump.  (see the section at the end to learn a little more about heat pumps).

  • Package units are very much like window air conditioners because the compressor, condenser and evaporator are all in one outside unit (B below).  Sometimes you can recognize a package unit if there is a large metal duct running from the unit into the home (sometimes, like in the diagram, the duct is hidden behind the unit).  Commercial rooftop units (A below) are often package units.  The advantage of these is that all of the noise and heat of the air handler is outside and the unit comes ready to be attached to the ductwork. 

(source diagram: refrigeratordiagrams.com)

  • Split units have the compressor and condenser located outside (unlabeled unit to the left below), while the evaporator/air handler is located inside.  Normally the evaporator/air handler is located in a closet, garage, attic or crawl space.  From this point the cooled air is distributed throughout the home via supply ductwork.  

Source diagram: thisoldhouse.com

Mini-Split systems are a takeoff of “central split systems” in that the evaporator is located inside, but air distribution ducts are eliminated.  For this reason, mini-splits are also called ductless systems, and because air ducts can be a source of energy loss, they are more efficient.  They used to supply refrigerant to only 1 evaporator (1 room), but modern units (Carrier for example) can supply refrigerant to up to 9 rooms. (thisoldhouse.com)  Instead of circulating cooled air through ducts, the refrigerant is sent into the home to small concealed or wall-, ceiling- or floor-mounted evaporator/fan systems.  It is a good solution for remodels and additions: instead of adding more ductwork or replacing a huge central unit that may be too small to serve the addition, add a mini-split to serve the new area.  Mini-splits can also be heat pumps to heat the area during winter (see section at end on heat pumps).

Mini-Split diagram source: armstrongair.com

Finally, portable air conditioners (PACs) are just that: you can move them from room to room easily, and even store them in a closet when not in use, because they are usually on casters.  Portable air conditioners are a type of “package” unit because the evaporator, compressor and condenser are all located in one unit, but it is inside.  In order to extract and remove all that heat, there are one or two hoses coming out of the unit, which must be run through a window or other opening.  If the unit only has one hose, the unit is sucking air from the room it’s cooling, running it over the condenser, and expelling it outside.  This creates a slight negative pressure in the room, in turn pulling un-conditioned air from any cracks and crevices in the room’s envelope.  Dual-hose units pull in outside air to cool the condenser, pushing it back out via the other hose, which is more efficient but can be a little more expensive and possibly more noisy.  In general, PACs are less efficient than window air conditioners, but their convenience to use (especially in climates where they are only needed several days of the year) makes them popular.  

source: whirlpool.com

Heat pumps: We mentioned that central air and mini-splits have the ability to heat as well as cool.  By reversing the flow of refrigerant, heat can be extracted from the air outside and carried inside.  These work well in mild climates that have temperate winters that don’t go much below 40 deg F.  

Source diagram: thisoldhouse.com

Purification that works with your air conditioner

What types of purifiers do we recommend with these different types of air conditioners?  We’re glad you asked!  Here is a table explaining what’s available:


Type of Air Conditioner

Type of Air Purifier

Central Package unit

Whole-Home Purifier

Central Split unit

Whole-Home Purifier


Air Angels + Germ Defenders


Air Angels + Germ Defenders


Air Angels + Germ Defenders


Of course, Air Angels and Germ Defenders are great portable solutions that you can use in any room even if you are also using a whole-home purifier, and HEPA units are also useful in high-dust or allergy-prone areas.  The Cleanroom WindPRO 650 is a great option for a large open space, with its electrostatic filter (can be washed) and carbon filtration against VOCs and odors. 

Although central air conditioning is very common, there are even more efficient ways to keep your home cool.  If you are planning a new home, consider geothermal cooling and heating, and High-Velocity Mini-Duct Systems are great for retrofits and older homes, because the small duct size can be aesthetically pleasing.   Whichever system you choose, make sure to do the best you can to seal the building envelope to prevent moisture, mold and dust issues.   Remember, temperature is just one factor of your healthy home climate!

Why, when and how do I clean my mini-split unit?

Why, when and how do I clean my mini-split unit?

Mini-splits are the elegant cousins of window AC units (even though some window AC units are pretty darn good-looking nowadays with lower profiles that don’t block your view).   Mini-splits and window AC units have some of the same internal parts, so even though mini-splits are usually less visible tucked up high on walls, they need the same attention as window AC units to perform efficiently and avoid harboring dust and mold.   (If you have a window AC unit, check out our article for deep-cleaning it here).  Dust and condensation (moisture) are the perfect breeding ground in a mini-split for mold, and it’s being blown directly into your indoor air. What we’re looking at today is cleaning the “indoor” part of the mini-split, which is in the top part of the diagram below.  The parts that can get very dirty are: 

  • the dust filter: it’s easy to take this filter(s) out and vacuum or wash it clean with mild soap and water every month

  • the cold coil (also known as the evaporator coil): deep clean at least once a year

  • Fan: deep clean at least once a year

  • the louvered cover (not labeled): deep clean at least once a year. 

Image source: What are Ductless Air Conditioning Systems?

When deep-cleaning the indoor unit, since it can’t be removed from the wall without releasing refrigerant (unlike the way you can lift the whole window AC out of the window and take it outside), cleaning the coils inside will require some good waterproofing to avoid getting water, cleaning fluid and dirt on your wall and floor.

The other inconvenient part about cleaning the indoor part of a mini-split is the location: since most of them are high on a wall, you will need a very sturdy ladder and perhaps someone to help by handing equipment to you as you need it. 

I like this video for a good method of a professional cleaning the indoor part of a mini-split unit.  It shows the preparation and equipment professionals use.   BUT you don’t have to be a professional–you can buy the “bib” cover online and use a simple garden sprayer to approximate the same cleaning power!  Here is a good video of a DIY guy doing an even more thorough job (he removed the blower wheel for cleaning outside) with a bit more detail on how to take off the louvers and cover.   The only things we cannot recommend is:

  • His choice of cleaners, which do contain toxic chemicals, some of which will be released inside.  

  • Also, make sure to wear safety goggles or preferably a full face mask!  You don’t want any moldy dirt to fly into your eyes or mouth while cleaning.

  • You can use a vacuum inside to remove big clumps of dust, however DON’T use a shop vac inside, unless it has a HEPA filter.  If your wet/dry vac doesn’t have a HEPA filter, then use any other vacuum that has a HEPA filter on the dry dust only.

For cleaning the inside unit, you can use:

  • Sturdy ladder

  • Goggles or face mask, (gloves–optional)

  • Flat and phillips screwdrivers (a power screwdriver is optional)

  • (1-2) 5-gallon buckets (at least one for inside, another one if you want to see what comes out of the evaporator drain)

  • Garden or pump sprayer

  • Bib for covering the unit for a cleaner job, $26: if you plan on doing your own maintenance, it’s worth investing in the cover to use every year!

  • Old towels

  • Coil cleaner (see below)

  • HEPA vacuum for any inside vacuuming

Regarding the coil cleaner, most aerosol coil cleaners have a “propellant” that assists with moving the liquid out of the spray can.  These propellants are usually hydrocarbons with VOCs.  You don’t need to buy spray coil cleaner and release this in your home!  Our choice of a non-toxic coil cleaner is Viper Evap+ from Refrigeration Technologies.  According to the Technical Data Sheet, it is the industry’s only non-rinsing evaporator coil cleaner utilizing slow-release enzymes in a synthetic detergent base, which is safe for all metals.  If it is not rinsed off, the enzymes remain on the coils for 72 hours, starving any microbes of oxygen.  The solution is gradually rinsed off by condensate production, which is drained via the condensate line.  It has no VOCs, TAC (toxic air contaminants) or HAP (hazardous air pollutants).  It is to be used full-strength via a pump sprayer (the garden sprayer we mentioned above works just fine). 

There are two natural cleaners we can recommend that are non-toxic.  The best part about these are the light citrus fragrance Please note that you should check the manufacturer literature on your mini-split unit to find out the recommended maximum acidity or alkalinity of any evaporator coil cleaning solutions, because strong acids or bases can eat metal and damage your unit!  Whichever you choose, you can check the acidity with a pH test strip after dilution to make sure it’s in a safe range for your unit.

  • For an acidic cleaner:  Nutribiotic is a grapefruit seed extract (GSE) which is highly acidic and microbial at full concentration (be very careful mixing and using it!) but can be diluted to use as a coil cleaner.  According to the manufacturer, The GSE Liquid Concentrate has a pH of about 2.75 and the Maximum GSE Liquid Concentrate has a pH of about 2.2, which are both very acidic.  In the article we found for using it to clean your car’s air conditioning evaporator coil, it’s recommended to use it at 2x manufacturer’s recommended dilution.  (Recommended is 10 drops per 5 oz water, so 2x strength is 20 drops per 5 oz water).  

  • For a basic (alkaline) cleaner: EarthClean by Earthpaint is a citric acid cleaner that is super-effective on greasy countertops, and when used at the manufacturer’s dilution, degreases safely on stone countertops with no damage.   Alkaline cleaners can remove greasy dust more easily, so if your mini-split is near your kitchen and your unit can tolerate an alkaline cleaner, this might be the best choice.

Mini-splits look great on the wall, but their performance is only as good as their cleanliness.  If you keep up with cleaning the air filter regularly (at least once a month), the unit will work better through the cooling and heating seasons, and won’t be nearly as gross or hard to clean during the yearly deep-cleaning.  You can save money by doing this yourself, but hiring a reputable technician is fine for those who have too many other things going on.  The most important thing is prioritizing good air quality in your home by performing or scheduling this type of cleaning regularly.