SyndicateHvac.com – Information about Air Handler Checks

An air handler is usually located in the garage, a closet, or in the attic (unless you
have a package unit then the air handler is incorporated in the system). It can be a part
of your furnace and houses the evaporator coils, the blower, and some controls. The air handler can be an upflow, downflow, or horizontal flow AHU (air handling unit). To determine
which one you have follow the return duct. The return duct should originate where you put the
filter and/or is the biggest register grill in the house. If the return ends in the bottom
of the unit it is an upflow air handler. If the return duct ends in the top of the unit it
is a downflow air handler. If the unit looks as if it is lying on it's side with the return
duct coming in one side the supply ducts going out the other it is a horizontal flow air
handler.




Knowing this information can help you find the filter if you have never changed
the filter in this unit. Some air handling units have the filter inside. If there is no filter
in the return register or grill then the filter is either in the return duct somewhere or
in the air handler itself. Filtering the air is not only important for the air quality in
your home but it is essential for the proper operation of the unit itself. The air must be
filtered before it reaches the coils or heat exchanger inside the air handler. If it is not
then there will be a build up over time of dust and debris that get sucked into the return.
This build up clogs off the evaporator coil and causes the heat exchanger to operate at
higher than normal temperatures. The unit becomes less and less efficient and will eventually

Spring maintenance checks to the air handler can help you avoid costly repairs when the heat of summer arrives. A word of caution is advised here before you open the panel. Air Handlers have high voltage running into them and there is a shock hazard. Before you remove the panel make sure the power is turned off to the unit. Only a professional should operate the unit with the panels off. Even with the thermostat in the off position the unit has high voltage running into it. Turn the circuit breaker off before opening any panel on your heating and air conditioning equipment. The air handler contains the evaporator, metering device (on most units), the blower, and some controls. The metering device and the controls should be checked by a professional. These components are highly technical and beyond the scope of this site to explain in detail. The evaporator and blower can be maintained by the homeowner as long as safety and common sense are applied.






Checking the Evaporator





The evaporator coil carries refrigerant inside it. This coil and refrigerant, through the heat exchange process, absorbs heat from the air passing through the coils. The heat causes the refrigerant inside the evaporator coils to boil and change state. The refrigerant, where it enters the coil, is mostly a liquid. By the time it reaches the end of the coils it should have absorbed enough heat to change it from a liquid to a vapor. On the outside of the air handler there are two copper lines. One large and insulated line, and one small and uninsulated line. The large line is the suction line. This line carries the vapor (refrigerant) back to the compressor in the condensing unit. The small line is called a liquid line. This line carries liquid (refrigerant) from the condensing coils to the evaporator. When the unit is running the liquid line should be hot and suction line should be cold. The temperatures of these lines will vary depending on how hot the house is inside and the ambient temperature outside the home. A big problem most people encounter with the evaporator coils is blocked coils. The coils are plugged with dust, dirt, and other debris, there is a duct collapsed somewhere, or there are too many supply vents closed off in the home. For the evaporator to work properly and efficiently the coils must be clean and have plenty of air flow. Thus, the necessity of a good filter to filter all the particles from the air before it reaches the coils. Coils operate below the dew point when the air conditioner is on. This will make the evaporator coil wet so when the dust makes contact with the coil it will often stick to the coil. Over time this will cause a build up and eventually the system will stop cooling. With improper air flow across the coils there is no heat exchange process. The coils will freeze and ice will form on them. Another cause of ice forming on the evaporator coil is a low refrigerant charge. If the coils are clean and they are icing up, you need to call a professional to charge the unit properly.




Cleaning the Evaporator Coils




Again, we recommend a professional do this work. A professional will have all the proper tools to complete the job quickly and efficiently. Make sure you follow the safety procedures noted above about cutting power to the unit before attempting to clean the coils. Once you have turned the power supply off from the air handler, open the panel where the suction and liquid lines run into the unit. Be very careful not to bend or crimp these lines or any lines in the air handlers. Another thing to avoid is the fins on the coils. Do not bend them. That would defeat the purpose of cleaning the coils because it will reduce the amount of air flowing across the coils. Check the drain line before you begin this procedure. See condensate drain section below for more information on this subject. Soak the coil with a soap and water solution. Professionals use an industrial strength coil cleaner which may be available at some hardware stores. Let this solution soak for a few minutes and then take a rag and wipe as much dust off the surface of the coils as possible. Repeat these steps until the coils look clean. Take a flash light and look between the fins. They should appear to be clean. If not, soak the coils again and use a brush with light bristles to brush the coils. Remove as much dust, dirt, and debris as possible. Remember there are two sides to the coil and make sure both sides are clean. The side that will most likely be dirty will be the side where the return air flow comes from. If your coils are clean and the rest of your components are operating normally you should have a nice cool summer inside your home no matter what the weather is outside.



Checking the Blower Motor




The blower is comprised of different components in most units. It has an electric motor, a squirrel cage blower wheel, and a cage typically referred to as a squirrel cage. Some units have belt driven motors and most have capacitors for the electric motor. The only required maintenace on the blower is oiling the motor if it has oil ports or checking the belt if you have a belt driven motor. Not all motors have oil ports. These motors use sealed bearings and never require oil. The motors that do have oil ports usually have little plastic dust caps that can be removed so that oil can be applied. They can be removed so that the bearings can be oiled. Not all motors have caps and not all caps are yellow.




Checking the condensate lines are especially important if your air handler is located in the attic. Since the evaporator coil operates at a temperature less than dew point, it will condense the moisture from the air. This coil is designed to allow the moisture to drip into a pan. Most pans have a 3/4" PVC line attached to them that allows the moisture to drain to the outside of the house. The PVC line often becomes clogged with algae and muck and needs to be blown or flushed out from time to time. If your air handler is in an attic it should have a secondary pan to catch the water in case the primary pan or line gets clogged. We recommend that all secondary pans have float switches installed. This switch will cut the unit off if the secondary pan starts to over fill. This will save you from buying a ceiling. Float switches can be installed by your local HVAC service company.




Check to make sure that the condensate line is not plugged by pooring water in the pan. If it drains fast then the line should be okay. If it drains slowly or not at all then the line is plugged or beginning to plug. Find the end of the line outside and take a hose and flush the line. You must be careful if you do this procedure. You can flood the pan and cause water damage. This will clean the line in most cases. If it doesn't you need to call a professional. They should have all the necessary tools to blow the line properly.




All of these checks can be made by your local heating and air conditioning company. Just call and ask for a spring tune up or a maintenance agreement. A little preventive maintenance can save you a lot of money in the future. Take the time to have this maintenance done and save yourself from the expense and hardship that comes with breakdowns.




In depth information:




By the time it reaches the end of the coils it should have absorbed enough heat to change it from a liquid to a vapor. What are the reasons why the coil wouldn't absorb enough heat to change the state of the refrigerant?




* Dirty Filters

* Dirty Coils

* Collapsed Duct

* Too many supply vents closed off

* A bad blower




The bottom line is airflow. There must be the proper amount of airflow across the coils for your system to operate efficiently. Take this one step further. If you have one of the aforementioned problems listed above and the refrigerant remains a liquid, what happens? Refrigerant leaving the evaporator is on a non-stop trip to the compressor. It is important that the refrigerant has changed from a liquid to a vapor before it reaches the compressor. Liquid doesn't compress and can cause major problems if it reaches the compressor. It's called liquid slugging and can cause irreparable damage to the compressor.