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Central Air Conditioning Systems

To maintain the energy efficiency, safety, and useful life of your central air conditioning system, it is important that your home maintenance program include the proper maintenance for your central air conditioner.


Central air conditioning has relatively expensive components (outside condenser unit, and inside blower and motor unit) and uses a significant amount of energy to operate.  Your air conditioning unit actually performs three functions: cooling, dehumidifying, and filtering out particulates from the air.  Your central air conditioning ductwork may be integrated as part of your home HVAC (heating ventilation and air conditioning) system.  Proper maintenance will help reduce unscheduled repairs to your home air conditioning system.  See also:  Forced-Air Heating System, Humidifiers, Dehumidifiers, and Heat Pumps.


Shown in the "Maintenance" tab above are the recommended routine maintenance tasks for your central air conditioner. The "Questions / Answers" tab above shows our answers to related questions. And the "Articles" tab above provides links to related informational articles and sources.

 

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 Maintenance Task #1Replace or wash air filter

 
       
    How do you replace an air conditioner air filter?  

 

 

This task involves removing the old air filter and replacing it with a new one (or washing the old filter, depending on the manufacturer's directions).  The filter is typically rectangular in shape, about 20 inches by 16 inches, and about 1 inch thick.  It slides into the main ductwork (near the inside fan unit) to help take dust, pollen, etc. out of the air that circulates in your home or building.  Ensure that the filters are placed in the correct direction of air flow.

 
       
    Why is it important to replace your air conditioner's air filter?  

 

 

There are two reasons for replacing this air filter:

  • As a filter gets dirty over time, it begins to clog with dust, pollen, etc.  A dirty filter means the fan motor of the air conditioner has to work harder to move air through it, which means it has to consume more energy, and is therefore more expensive to operate.

  • The filter helps to clean the circulating air, which makes room cleaning easier and less frequent, helps improve home health air quality, and helps to provide relief to allergy sufferers.

 
       
    How often should you replace your air conditioner's air filter?  
    The air filters should be replaced monthly during the heavy cooling season months (April through August).  

 

 

 

   
    How does Home-Wizard rate the costs and benefits for this task?  
    The cost of this task is relatively low.  It is estimated that this task should only take about 15 minutes to complete, and the task is relatively easy to do.  No specialized tools are required.  However, you do need to purchase the appropriate filter for your air conditioner's air handler in advance.  
         
    The benefits of this task are moderate, as a dirty filter requires more energy to operate your air handler.  Also, if people in your house have respiratory problems, then this task becomes more important.  
       
    Overall Home-Wizard benefit-versus-cost rating (one 'hat' = low and four 'hats' = high)  

 

 

 

 

 

 Maintenance Task #2Clean water drain

 
       
    How do clean your air conditioner's water drain?  

 

 

When an air conditioner cools the temperature of the air, water condenses out of the air (similar to the way water condenses on the outside of a cold drinking glass on a hot day).  Most central air conditioning units have a condensate drain to collect this water.  This is typically located on the side of the inside fan unit.

This condensation system and drain should be inspected to make sure there are no obstructions, and that the hoses all fit properly.

 
       
    Why is it important to clean your air conditioner's water drain?  

 

 

If the lines or drain becomes blocked or develops leaks, the result could be water spilling out around your unit, which can cause safety hazards and/or water damage.

 
       
    How often should you clean your air conditioner's water drain?  
    The condensate drain should be inspected every April before the cooling season.  

 

 

 

   
    How does Home-Wizard rate the costs and benefits for this task?  
    The cost of this task is very low.  It is estimated that this task should only take about 10 minutes to complete, and the task is relatively easy to do.  No specialized tools are required.  
         
    The benefits of this task are relatively high.  Doing this task can help prevent serious damage from water leaking in your home, especially if your air handler is located in the attic.  
       
    Overall Home-Wizard benefit-versus-cost rating (one 'hat' = low and four 'hats' = high)  

 

 

 

 

 

 Maintenance Task #3Clean outside condenser unit

 
       
    How do clean your air conditioner's outside condenser unit?  

 

  The "outside condenser unit" is the big box with the large fan in it located on the side of your house or building.  This unit is where heat from the inside of your house is pushed to the outside (which is why the fan blowing air above the unit feels warm).  Inside of the box are coils of pipe that are surrounded by thousands of thin metal "fins".  These fins give the coils more surface area for exchanging heat.

Cleaning the outside condenser unit involves four activities.  Before doing any of these activities, be absolutely sure to shut off power to the unit and consult your owner's manual regarding discharging the capacitor and proper maintenance procedures for your unit.  If you have any questions about how to do this, seek professional maintenance help.

  1. Remove leaves, debris, spider webs, etc. from the outside of the unit.  Be careful to push debris away from the fins, not pushing debris into the fins.  
  2. Remove leaves, debris, etc. from the inside of the unit (after ensuring that power is shut off to the unit).  After you remove the cover grille, you can use a garden hose to spray the coils from the inside of the unit.
  3. If any of the fins are bent, you can use a special tool called a "fin comb" to straighten and clean them.
  4. The motor which drives the fan typically has ports which allow lubricating oil to be added (check your owner's manual).
 
       
    Why is it important to clean your air conditioner's outside condenser unit?  

 

 

The purpose of this maintenance task is to help maintain the energy efficiency of the condenser unit.  A dirty unit is less efficient at doing its job, which means that your air conditioning unit has to work harder, which causes it to consume more energy, and shortens its service life.

 
       
    How often should you clean your air conditioner's water drain?  
    The outside condenser unit should be cleaned every April before the cooling season.  

 

 

 

   
    How does Home-Wizard rate the costs and benefits for this task?  
    The cost of this task is moderately high.  Cleaning the outside of the unit only takes a few minutes.  But cleaning inside the unit and oiling the motor is much more difficult, and straightening the fins requires a special tool.  This part of the task is probably best left to a trained professional, as part of your annual service work.  
         
    The benefits of this task can be somewhat high because this task helps ensure the energy efficient operation of your air conditioning unit, and it helps maintain the useful life of a relatively expensive piece of equipment in your home.  
       
    Overall Home-Wizard benefit-versus-cost rating (one 'hat' = low and four 'hats' = high)  

 

 

 

 

 

 Maintenance Task #4Cover (and uncover) outside condenser unit

 
       
    How do cover (and uncover) your air conditioner's outside condenser unit?  

 

 

Covering the outside condenser unit involves placing a plastic or cloth cover over the unit.  This cover can be purchased pre-made, or you can "do-it-yourself" by taping together plastic trash bags, or a plastic drop cloth, etc.

 
       
    Why is it important to cover (and uncover) your air conditioner's outside condenser unit?  

 

 

The purpose of covering the unit when it is not in use is to keep leaves, dirt, freezing water, etc. away from the condenser.  Keeping the unit clean helps to maintain its energy efficiency and extend its service life.

 
       
    How often should you cover (and uncover) your air conditioner's outside condenser unit?  
    The cover should be put on in September, after the cooling season is over, and then should be taken off in April, before the cooling season.  You should also turn the outside electrical switch to "off" when the cover is put on, and then turn the switch to "on" when the cover is removed; this is so you don't operate the air conditioner while the cover is on.  

 

 

 

   
    How does Home-Wizard rate the costs and benefits for this task?  
    The cost of this task is very low.  It is estimated that this task should only take about 20 minutes to complete, and the task is relatively easy to do.  However, you will have needed to purchase the tarp cover in advance.  
         
    The benefits of this task can be somewhat high because this task helps ensure the energy efficient operation of your air conditioning unit, and it helps maintain the useful life of a relatively expensive piece of equipment in your home.  
       
    Overall Home-Wizard benefit-versus-cost rating (one 'hat' = low and four 'hats' = high)  

 

 

 

 

 

 Maintenance Task #5Close (and open) air distribution registers

 
       
    How do you close (and open) your system's air distribution registers?  

 

 

Air distribution registers are the duct openings on your walls, floors or ceiling where the cold air conditioning air comes out.  These registers typically have a lever or wheel that allows the register to be opened and closed.

After your air conditioning system has been shut down for the season, these registers should be closed.  They should be opened again before you start up the system in the Spring.

Make sure the registers are not blocked by furniture, carpeting, or drapes.

 
       
    Why is it important to close (and open) your system's air distribution registers ?  

 

 

Closing these registers keeps warm air from being lost by back-flowing through these vents in the winter.  It also keeps dust, pests, etc. from accumulating in the ducts when they are not in use.

 
       
    How often should you close (and open) your system's air distribution registers ?  
    The registers should be closed in September after the cooling season.  Open again in April before the cooling season begins.  

 

 

 

   
    How does Home-Wizard rate the costs and benefits for this task?  
    The cost of this task is very low.  It is estimated that this task should only take about 20 minutes to complete, and the task is relatively easy to do.  No specialized tools are required.  
         
    The benefits of this task are relatively high.  Doing this task can help prevent serious damage by pests, including termites, which can be very costly to eliminate and repair damage from.  
       
    Overall Home-Wizard benefit-versus-cost rating (one 'hat' = low and four 'hats' = high)  

 

 

 

 

 

 Maintenance Task #6Air duct cleaning

 
       
    How do you clean your air conditioning system's air ducts?  

 

 

A professional service company typically uses specialized tools to dislodge dirt and debris in the ducts and then removes it with a high-powered vacuum cleaner.  In addition, the service provider may also have treatments for killing microbiological contaminants.

 
       
    Why is it important to clean your air conditioning system's air ducts?  

 

 

Leaving moisture, dust, pollen, etc. in your ductwork can create a breeding ground for molds and spores which affects your home health.  Cleaning the ductwork removes these contaminants and also increases the air flow efficiency of your ductwork which can save energy.

 
       
    How often should you clean your air conditioning system's air ducts?  
    You should clean your air ducts in April prior to the cooling season.  

 

 

 

   
    How does Home-Wizard rate the costs and benefits for this task?  
    The cost of this task is moderately high, as you will need to hire a professional firm to do this task.  
         
    The benefits of this task are the modest amount of increased energy efficiency that you can see.  But if you have people in your home with respiratory issues, then the benefits to this task can be significant.  
       
    Overall Home-Wizard benefit-versus-cost rating (one 'hat' = low and four 'hats' = high)  

 

 

 


 

QUESTIONS & ANSWERS from "Ask-a-Wizard":



QUESTION from mzhignz on 8/2/2008
My central air unit is running but no air is blowing from the registers...What should I check?

ANSWER FROM HOME-WIZARD.COM on 8/2/2008
Dear mzhignz:

If your outside air conditioning unit is running, but you are not getting any air flow coming out of your registers, then I would suggest checking to see if you have blown a fuse (or tripped an electrical breaker) on your inside air handler unit.

Most central air conditioning units have two circuit breakers, one for the inside unit and one for the outside unit, and they will be located in the main electrical panel for your house. If you need to replace the fuse for the inside unit BE VERY CAREFUL as your air conditioning system is wired for high voltage. If you are unsure of yourself, then this may be something that you will want to have a trained professional do for you. If you have switch-style electrical breakers, check to see if the breaker in your electrical panel for your house has clicked into the "off" position. If it has, then move it over to the "on" position. If it clicks back to the "off" position, then you likely have a short-circuit in your air conditioning unit, and you will need to call a professional to inspect it.

If your problem is not due to a blown fuse or tripped circuit breaker, then other possible causes include:

o fan belt is broken in your inside air handler unit.

o someone accidentally turned off the switch located on the side of your inside air handler unit.

o very clogged air filters.

o or if your system is electrically zoned, then the zone dampers may be stuck in the closed position.


Hope this is helpful.
Home-Wizard.com
____________________

QUESTION from peter on 8/15/2008
The neighbor in the video mentions planting shrubs around the A/C unit to make it more energy efficient. Please explain.

ANSWER FROM HOME-WIZARD.COM on 8/15/2008
Dear Peter:

. . . sure, glad to explain.

The short answer is that placing shrubs around it, the shrubs help to keep your outside air handling unit at a lower temperature (by blocking the sun and providing shade), so that it makes this air handler's job easier. Since your outside air handler's job is to draw the heat away from the inside of your house, if this air handler is baking in the sun, it gets hot and makes it harder for the unit to get the heat away.

For a longer answer on how a home air conditioning system works, this webpage provides a fairly good explanation:

http://www.hometips.com/cs-protected/guides/airconditioners/aircond_works.html

One thing to consider when planting shrubs around an outside air conditioner unit, is that you do not want to place the shrubs so tightly around the unit that it doesn't leave room for the unit to "breathe". Air needs to circulate freely around the unit, so that it can easily dissipate the heat that it has brought from inside your house.

One last thing to consider is whether your AC unit is already in the shade. If your house, trees, etc. are already shading the unit, then you don't need to add the shrubs.

Hope this is helpful.

If you have additional questions, just let us know.

Also, we hope that you are finding our monthly videos to be both informative and entertaining.

Sincerely, 
Home-Wizard.com
____________________

 

QUESTION from Larry on 12/28/2008
I read the info regarding closing down the central air conditioning system for the winter, but I saw nothing about blocking off the air return. I thought this was very important to prevent condensate from water damaging the home. Am I wrong?
____________________

ANSWER FROM HOME-WIZARD.COM on 12/28/2008
Dear Larry:

Actually, on our webpage for maintenance tasks for central air conditioning in our Maintenance Library (http://www.home-wizard.com/maintenance/airconditioning.asp), Maintenance Task #5 describes closing the air return registers when you close down your central air conditioning system for the season. 

And you are correct, since air conditioning ducts can sometimes be run through unfinished (unheated) attic spaces, leaving these air return registers open can not only lead to heat loss, but also, introducing warm air into cold attic spaces can lead to water condensation problems.

Regards,
Home-Wizard.com

FOLLOW-UP QUESTION from Larry on 12/28/2008

Thanks so much for the prompt response. 

Larry
____________________

QUESTION from TILLMAN122 on 8/8/2009
WHY IS MY CENTRAL AIR CONDITIONING FREEZING UP

ANSWER FROM HOME-WIZARD.COM on 8/9/2009

Dear Tillman122:

There are a number of possible reasons why your air conditioner is freezing up:

1. Your air conditioner may be running low on refrigerant. Low refrigerant levels can cause the coil to become too cold. You will need to contact a professional to find and fix your refrigerant leak, and to re-charge your unit with refrigerant.

2. You may not have enough airflow to keep the coil from freezing. Air from your house passing past your coil keeps it above freezing because this air is above 32 degrees fahrenheit. If there is not enough airflow, the coil gets too cold and starts to freeze the condensed water before it can drain away. To prevent this, check for a dirty air filter. Depending on your system, you should be changing your air filters once a month during the cooling season. And also, make sure that your registers are all open and clear, so that air can flow freely.

3. Make sure your fan is actually moving air when your air conditioner is running. If your air conditioner is running and the fan is not always running (or not running fast enough), then this could be the cause of your freezing.

4. If you have a bad thermostat and it allows your air conditioner to run all night during a cool night, then this could cause your air conditioner to freeze up (although in your particular case, it sounds like your problem is occurring during the day).

Remember, if you let your air conditioner continue to run after the coil has frozen up, then you are not only wasting money, but you are also risking damage to the compressor, which is very expensive to replace.

Hope this is helpful.
Home-Wizard.com
____________________



QUESTION from Jose on 8/31/2009
During the last few days, my AC unit has not cooled my house below 86 degrees. (The ambient temperature has been around 90-95 degrees) The condensor seems be working. I've changed the filter. But, not much cool air seems to be coming out of the vents. Any ideas about what could be wrong?

ANSWER FROM HOME-WIZARD.COM on 8/31/2009

Dear Jose:

Here is a webpage that describes how to diagnose problems with an air conditioner:

http://www.inspect-ny.com/aircond/aircond15e.htm#bannertop

As you will read, since you have already changed your air filter, some other things to check include: 

o Check to evaporator in the inside unit to see if it is it frosted up. 

o Check to see if you have condensation water in the pan.

o Go to the outside unit and feel the air coming out of the fan. Is it warm? 

o Then feel the two copper pipes coming out of the outside unit. Is the small one warm or hot? Is the larger one cool ?


Hope this is helpful.
Home-Wizard.com
____________________

QUESTION from Joe on 9/17/2009
A/C compressor fins have developed a white coating. Appears to be some type of oxidation. Is there any way to clean it?

ANSWER FROM HOME-WIZARD.COM on 9/17/2009

Dear Joe:

The white coating could be oxidation, or it could be residue if an acid cleanser was previously used.

Here is a webpage that describes how to clean air conditioner compressor fins: http://www.ehow.com/how_5064669_save-own-air-conditioners-condenser.html

Also, if you see a number of bent fins (or if you accidently bend some of them when you are cleaning the fins), then you might want to consider using a "fin comb" to straighten them back out. And here is a short video on how to use a fin comb: http://www.youtube.com/watch?v=mwzwboqN5Cw

Hope this is helpful.
Home-Wizard.com
____________________


QUESTION from chicky on 9/27/2009
How can you remove the ice accumulated inside the airconditioning unit? And how can we prevent it?


ANSWER FROM HOME-WIZARD.COM on 9/27/2009

Dear "chicky":

There are a number of possible reasons why your air conditioner is freezing up:

1. Your air conditioner may be running low on refrigerant. Low refrigerant levels can cause the coil to become too cold. You will need to contact a professional to find and fix your refrigerant leak, and to re-charge your unit with refrigerant.

2. You may not have enough airflow to keep the coil from freezing. Air from your house passing past your coil keeps it above freezing because this air is above 32 degrees fahrenheit. If there is not enough airflow, the coil gets too cold and starts to freeze the condensed water before it can drain away. To prevent this, check for a dirty air filter. Depending on your system, you should be changing your air filters once a month during the cooling season. And also, make sure that your registers are all open and clear, so that air can flow freely.

3. Make sure your fan is actually moving air when your air conditioner is running. If your air conditioner is running and the fan is not always running (or not running fast enough), then this could be the cause of your freezing.

4. If you have a bad thermostat and it allows your air conditioner to run all night during a cool night, then this could cause your air conditioner to freeze up (although in your particular case, it sounds like your problem is occurring during the day).

Remember, if you let your air conditioner continue to run after the coil has frozen up, then you are not only wasting money, but you are also risking damage to the compressor, which is very expensive to replace.

Hope this is helpful.
Home-Wizard.com
____________________

 




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