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Phone: 540.373.8471
Fax: 540.373.8393
26 Town & Country Drive
Fredericksburg, VA 22405
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We service all makes and models of ACs, heat pumps, and furnaces.

Diagnosis Dictionary

Questions regarding a diagnosis for your HVAC system?  Below are "layman's terms" defnitions of HVAC system components.  Feel free to call us at 540-373-8471 with any questions.  This list is being added to on a weekly basis--check back frequently! 

ACCUMULATOR:  This is a storage tank in your outdoor unit that receives the liquid freon pumped from the evaporator coil.  It holds (accumulates) both oil and freon, keeping them from entering the compressor on the outdoor unit.  Both freon and oil are harmful to your compressor. 

BLOWER WHEELOften referred to as a "squirrel cage," (because it looks like a hamster wheel that's been re-sized for a squirrel), the blower wheel is located in your air handler (indoor unit).  The blower wheel is responsible for pushing air through your home.  Powered by a blower motor, the wheel can get out of balance and clogged with dirt or debris, prohibiting adequate airflow into the home.     

A CAPACITOR is an electrical component that stores energy.  It gathers and stores power while the unit is in operation, and releases the charge when needed at time at start-up.  Capacitors control the start-up of your outdoor unit's fan and compreesor.   If your system is blowing air, but it is unheated or uncooled--this could be indicative of a bad compressor (although other components could be the issue).   Capacitors are round or oval cylanders, and will bulge and even burst when they are going bad or are completely blown.

CAPILLARY TUBE:  One of the many elements of an HVAC system's performance is proper control of freon flow--each system requires a finite amount of freon to pass through components, and at specifc levels of pressure.  One of the devices that controls freon flow & pressure is a capillary tube.  A capillary tube isn't too unlke a capillary in your body--it has a very small diameter and can be quite long in length.  When freon hits the tube, it's small size immeidately restricts the flow of freon--think of a water balloon attached to a drinking straw--squeeze the balloon and only so much water can pass through the straw.  The diameter and length of the capillary tube dictates how much freon passes through the system. As with a capilary in your body, an HVAC system's capillary tube can become clogged, causing too much fron restriction and hindering (or even eliminating) system performance.  A number of things can clog a capillary tube--one example is moisture in the system (caused by a technician not vacuuming out a unit long enough).  Another issue is improper brazing of copper lines--this can cause soot to form on the inside of the pipe.  As freon flows through the line, it catches this soot and carries it thorughout the unit.  most will get caught in the system's filter drier, but smallter soot particles can get stuick in the capillary tube.  Both of these issues bolster the adage "your system is only as good as your installer."    

 A COMPRESSOR is literally the heart of your system. It pumps freon from the indoor unit to the outdoor unit (and vice-versa depending on the season).  Located in the middle of the outdoor unit, the compressor is one of the hardest working parts in your HVAC system. Dirty filters and coils put strain on your compressor and will lead to burnout. Solution?  Frequently change the filters in your home (at least once a month). Also, keep your outdoor unit free from obstructions—give at least 2 feet of space between the unit and any shrubs, latticework, etc. (both around AND above the unit). When you look at the outdoor unit, you will see delicate metal fins around the perimeter of the unit (this is your condenser coil). Air is constantly being pulled through these fins, and any number of things will get on these fins and clog them up (leaves, dirt, pet hair, etc.), which in turn puts strain on the compressor. It is perfectly fine to GENTLY rinse these fins to keep them “breathing” properly.

COMPRESSOR, HERMETIC:  A unit in which the compressor and motor are sealed in the same housing.  

CONDENSATE LINE:  Your evaporator coil pulls humidity from the air in your home, and this translates into--condensation!  Your system is designed to drain this water safely away from your system and out of your home through the condensate line (and condensate pump when gravity needs a hand).  Made of tubing, these lines will eventually become clogged with mildew and other gunk--a normal feature of the condensation draining process.  Periodic cleaning, flushing, and blowing out the lines is a part of our Comfort Club Maintenance Agreement--and it's critical!  Give our office a call--we can give you advice on using bleach as a DIY tool to keep your lines clean between checkups!      

CONDENSATE PUMP:  Condensate pumps are a critical part for most frunaces, straight ACs, dehumidifiers, and heat pump systems.  All of these systems produce condensation, and your condensate pump gets this water out of your home (via the condensate lines).  Failure of the pump will result in water pooling around the base of your systems.  Most pumps have a hole in which you can add bleach water to help keep yoru condensate lines free and clear of mold--give us a call for advice before you try this technique.     

CONDENSER COIL: The condenser coil is located on the perimter of your outdoor unit.  The condenser fan pulls outside air into the system, and the coil cools the super-heated air created by your hard-working compressor.  Classified as a heat exchanger, the condenser coil needs to be kept free of debris to allow it maximum "breathability."      

CONDENSER FAN/MOTOR:  This fan sits on top of your heat pump or straight AC's outdoor unit.  It provides the air needed for your condenser coil (see above) to function.  It should always run whenever your outdoor unit is running, except for periods when the unit is in defrost mode.     

DEFROST CONTROL BOARDAs its name implies, this board controls the defrost cycle on your outdoor unit.  Outdoor units poroduce tremendous amounts of heat, and in the wintertime this will result in frost on the coil.  The defrost cycle eliminates this frost and allows the system to run smoothly.  You may have noticed your unit emit a loud "whooshing" sound, with steam rising from the top of the unit.  This is the defrost cycle at work.  It is normal for your outdoor unit to develop frost, but if you see it get thicker than 1/8", give us a call to check it out--there's a good chance that the defrost sensor or control board is faulty. 

DEFROST SENSORThe defrost sensor is attached to your outdoor unit's coil, and it regulates the coil's temperature.  As mentioned above in the Defrost Control Board information, heat from the outdoor unit's operation will cause frost to form on the coil (only during the winter).  This frost steadily drops the temperature on the coil, and when it reaches a certain point, the sensor sends a message to the Defrost Control Board, telling it to get to work.  You can see this process at work when you hear a "whoosing" sound and see stea rising from the top of the unit.     

DIRTY SOCK SYNDROME: This issue causes, as the name implies, a strong smell of sweaty socks throughout your home.  It is generally caused by a dirty evaporator coil.  Evaporator coils are either in your heat pump's air handler or the cased coil that resides above/beside your furnace.  Certain microbes that get into the coil will emit a foul odor as they break down and go through the process of being heated or cooled through the normal process of refigeration.  The resolution to this issue is a thorough coil cleaning or somtimes replacement of the entire coil is necessary.  How can you avoid this problem?  CHANGE YOUR FILTERS ON A REGULAR BASIS--AT LEAST ONCE EVERY THREE MONTHS, MORE OFTEN IF YOU HAVE A LOT OF FUR/HAIR/DUST IN YOUR HOME.  Changing your filters keeps a lot of problems at bay, not just this syndrome!   If your home has an issue with any kind of persistent odor and filter changes don't do the trick, installation of a UV light could be the solution--give us a call for more info.   

DRAIN PANLocated beneath your evaporator coil (in the air handler/indoor unit), the drain pan catches all the moisture produced by the evaporator coil.  Attached to the pan is a condensate line for proper draining of the 

DUCTLESS MINI-SPLIT:  Mini-split systems are heat pumps that require no ductwork.  As with a traditional heat pump,  mini-split systems have two components--an outdoor condensing unit and an air handler inside your home.  Here the similarities end.  The indoor unit of a mini-split is a wall-mounted unit that conditions and blows air directly from the unit itself.  This eliminates the need for ductwork--the outdoor and indoor units are connected only by refrigerant piping.  One outdoor unit can handle up to eight indoor units.  Mini split systems are extremely quiet and extremely efficient.  They are ideal for remodels and new construction projects where space for ductwork is an issue.    

EVAPORATOR COIL: Located inside the air handler (indoor unit), the evaporator coil removes heat and humidity out of your home. It is responsible for distributing cooled air through the ductwork. In short, the evaporator coil absorbs the heat from the building and allows free flow of the cooled air.  This is very similar to the process of a cold drink forming condensation on the outside of its can or cup. The evaporator coil moves the water to the condensate drain, removing the vapor from the cooled area, which results in lower humidity in the air.  The best way to protect your evaporator coil is by changing your filters frequently.  Dirt that gets through a dirty filter goes straight to your evaporator coil.  The dirt clogs the delicate fins of the coil, which can lead to the coil freezing up and eventually failing. 

FILTER DRIERLocated either in your outdoor unit, or installed just outside the unit, a filter drier is connected to the liquid freon line and captures any contaminents, preventing them from getting into (and subsequently damaging) your compressor.  Some systems come with factory-installed filter driers.  If not, they are added at the time of installation.     

FLA (FULL LOAD AMPERAGE):  You may notice a reference to "FLA" in the writeups for your seasonal checkups or in the diagnosis of bad or failing motors.  FLA = Full Load Amperage, which is simply the current draw of a motor under full load, or the current flow in a circuit when the load is at its rated peak.     

FUSE: A metal strip in an electricla circuit that melts and breaks the circuit when excessive current flows through it.

HEAT EXCHANGER:  This is a critical part of your gas furnace.  In essence it is the part that actually provides  heat, with your blower dispursing the heat into your ductwork.  Ignited gas passes into the heat exchanger, of course causing it to get hot.  The heat coming off the exchanger is then blown into your ductwork by the furnace's fan.  Constructed of steel, a heat exhanger can become rusty and develop holes.  Water can come from a leaking evaporator coil, or from the natural condensation that forms from combusted gas.  Holes in your heat exhanger are dangerous, as it allows carbon monoxide to be released throughout your home!  This issue is one of the reasons that a yearly checkup of your system is so very important.  In addition to routine checkups, it is critical that you have  carbon monoxide detetcors throughout your home.  The best detetcor to purchase is one that plugs in and also has a battery backup.  Keep in mind that carbon monoxide is odorless, so a good detetcor is critical to your family's safety.  We sell quality carbon monoxide detectors--give us a call for a quote or for a recommendation on one you can purchase at hardware stores. 

HIGH LIMIT:  You may get a diagnosis for your gas furnace that states "system going out on high limit."  This means that your furnace's internal temperature has reached an unsafe level (potentially caused by clogged filters or a fan not working), and the high limit is typically a heat-sensitive switch that shuts your system down in the event of unsafe heat levels.  This saves, among other things, your heat exchanger from cracking.   

HOT SURFACE IGNITOR:  A hot surface ignitor, commonly reffered to as an "HSI," is an integral part of your gas furnace.  Unlike older furnaces that used a standing pilot light to ignite the burners on the furnace, many of today's models use an electronic ignition system. This includes a Hot Surface Igniter, sometimes referred to as a glow plug or glow stick. When there is a call for heat, the igniter receives electrical current in order to heat its surface and ignite the burners in the furnace. Some hot surface igniters are fairly fragile and can be damaged during transit or installation.  Cracks in a hot surface igniter are not necessarily visible. After installation, the glow pattern should be routinely checked for inconsistencies, and replaced if necessary. Cracks will not necessarily prevent the igniter from working, but will shorten its life. It is important that the correct original equipment manufacturer's igniter be used for replacement.  While an HSI provides a more efficient and cost-effective method for gas ignition, they typically fail every few years.  The overall savings the HSI provides well exceeds the cost of the part itself.  Checking the HSI is a part of our routine Comfort Club Maintenace Agreement checkup. 

HSPF - Heating Seasonal Performance Factor--this is a number that measures the efficiency of an air-sourced HVAC unit (such as an electric straight AC or heat pump).  Similar to the more commonly known SEER rating--looking at both SEER and HSPF paints a good overall picture of a system's efficiency.  Rule of thumb--the higher the HSPF rating of a unit, the more energy efficient it is.  The higher the HSPF rating of a unit, the more efficient it is.  HSPF is actually a ratio of BTU heat output over the heating season to watts-hours of electricity used.  HSPF is measured in watts/hour. 

HUMIDIFIER:  One of the unfortunate results of heating your home is dryness.  Gas heat in particular can wreak havoc in this arena, causing sinus issues, static electricity, and cracks in hardwood flooring/furniture.  A simple solution is a whole-house humidifer.  Installed on your air handler, a whole-house humdifier pumps moisture into the heated air that is dustributed throughout your home.  One customer told us that his humidifier is like "lotion on his hardwoods."  It's an apt description!  In addition to saving your flooring, a humidifier indeed "soothes your sinuses and stops the static." 

HVAC - The term "HVAC" stands for "heating, ventilation, and air conditioning."  The term refers to "the technology of indoor and vehicular environmental comfort. (source--Wikipedia)."  The world of HVAC is incredibly complex.  Technicians that are truly qualified to work on HVAC systems need years of both education AND field experience.  Ask if the tech coming to your home has both (education and field experience) before you let them work on your system.  At COmfort Heating & Cooling, we require all our techs have at least five years in the field.  As an example of the complexity involved with HVAC technology----let's take a very broad and basic look at how a heat pump works.  These systems take a fluid (freon) that is over 400 degrees below zero and proceeds to boil that fluid into a vapor.  The direction of the freon flow determines if the system generates cool or hot air.  There are a pantheon of parts needed to make this process happen, coupled with almost as many parts to make the process run safely.  The refrigeration cycle is pretty amazing, and we nedd to keep in mind that it has to happen over and over again--every day, all day.  The complexity of tHVAC technology means that accurate diagnosis of problems requires an immense book of knowledge, and again that all-important field experience.  While installation of HVAC systems is a little more straightforward than diagnosis, it still requires both knowledge and experience to ensure that everything is done correctly and within manufacturers' specifications.  Many installation issues will not manifest themselves immediately--some may not rear their ugly heads for months, even years down the road.  The technology of HVAC, also known as "the Technology of Climactic Comfort," is a fascinating example of engineering mastery and ingenuity. 

METERING DEVICE: Controls the flow and evaporation rate of the freon in the evaporator coil. The two most common metering devices are TXVs (thermal expansion valves) and EEVs (electronic expansion valves).      

MUFFLER - Heat pump and straight AC outdoor units typically have factory-installed mufflers.  They play two important roles in the operation of your system.  First--as the name implies, one function is to reduce noise.  The compressor (heart and soul of an outdoor unit) compresses and pushes refrigerant through your HVAC system.  The process of discharging refrigerant from the compressor is quite noisy, and the muffler dramatically reduce this noise.  Second--a muffler does more than just reduce noise.  Your compressor discharges freon in pulses--if the pressure levels were put on a chart, you would see a wavy line with peaks and valleys--like the sine waves from back in your math class days. Optimal sysrtem performace calls for a steady flow of freon pressure.  Your muffler helps convert pulsing pressure to a smooth steady pressure.    

MINI SPLIT: Also as "ductless mini split," these are heat pump systems that, as the name implies, do not require ductwork.  They are extraoridinarily efficient, and very small in size.  The air handler (indoor unit) is mounted on the wall or ceiling, and have a very small footprint (average wall-mounted unit size is about 30" wide and 11" tall).  Where a traditional heat pump system will require numerous wall penetrations for grills, these units only require one penetration for the line set (the coppe rline connecting the indoor and outdoor units).  They are perfect solutions for retrofiit and remodeling jobs, and sometimes the only solution for homes that simply don't have room fur ductwork. 

Standard heat pumps have efficiency ratings of 13 Seer, with top-of-the-line units achieving as high as 18 Seer.  Base model mini split systems start with 18 Seer efficiency ratings, and go up to 28 Seer!  The key to these units' effciency is an "inverter compressor."   The best way to describe how these inverter compressors work is to copare it to a vehicle.  imagine having a gas pedal in your car that cannot be feathered...you can either have the gas pedal floored, or have your foot completely off the pedal.  So to achieve a 60 mph speed, you would be constantly compressing and letting off the pedal, doing your best to stay around 60 mph.  Of course you would at times be in excess of your desired speed, other times below it as you try to maintain a steady speed.  Imagine how much gas you would burn driving this way!  This is how a standard heat pump comressor works--either it pumps full blast, or not at all.  Inverter compressors emulate the way your gas pedal really works--you can feather the pedal to your desired speed, making it a cinch to keep you at the speed you need.  Inverter compressors can ramp up ande down based on the desired temperrature.  This means a massive savingg in your electric bill as well as a tremendous increase in overall efficiency.  So in addition to utility bills savings and less holes in your walls, mini split systems are extremely quiet, running at about the same decible level as a refrigerator!   Higher Seer standard heat pumps typically require variable speed air handlers, which can be quite noisy.   Mini split technology is used extensively in Europe, where old buildings do nothave any room for ductwork.  Mini split sales are nwo starting to skyrocket in the U.S., as more and more contractors embrace the technology, and customers are starting to see the huge savings in their utility bills.  Call us for more information and an estimate!            

PRESSURE SWITCH (GAS FURNACE): Controls the amount of draft pressure in your flue.  Proper draft pressure is critical--low draft pressure can cause carbon monoxide to enter your home.  Too much draft pressure will cause your unit to not fire. 

 PUMP-UPS/SNOW LEGS: Pumps-ups are used to raise your outdoor unit off the ground--typically made of plastic, they are either 3" or 6" in height. They are important in areas with large amounts of snow, allowing the consdenser unit to continue "breathing" even if there is snow on the ground.

A RELAY is an electrical component that basically acts as an on/off switch. Relays control your indoor unit's fan. You may have noticed that when your system turns on, the indoor unit's fan will energize shortly thereafter--that's your relay at work! Relays cometimes get stuck, causing your unit to either run continuously (if stuck in the ON position), or not at all (if stuck in the OFF position). A blown relay will not allow the system to run at all.SEER: "Seasonal Energy Efficiency Ratio." This is the standard of measurement for the efficiency of heat pumps and straight ACs. The higher the SEER, the more efficient the system. SEER level is calculated by taking the cooling output of a typical cooling system and dividing it by the total electrical energy used during the same time period. The lowest SEER allowed by federal law is 13, although this will be changing in 2015 to 14. The maximum efficiency available in most heat pump and AC systems is 18, although mini split (ductless) systems can achieve SEER ratings in the high twenties.

SHORT CYCLING:  What does it mean if your system is diagnosed as "short cycling?"  This issues can apply to heat pumps, straight ACs, and furnaces.  In the case of heat pumps and ACs, the units go through a "refrigeration cycle," during which freon is converted from liquid to vapor (or vice versa).  Depending on what direction the freon is flowing, a complete refrigeration cycle will produce either hot or cold air.  Gas furnaces also have a cylce, in this case producing only heat.  Short cycling simply means that the process is happening faster than it should.  One example of short cycling is an oversized unit.  Every unit takes a certain amount of time to complete a full refrigeration cycle, and in the case of an oversized unit set point temperatures can be achieved before the cycle is complete, causing the unit to shut down too soon.  The result is a system that is constantly starting and stopping.  This puts pressure on all the components in the system and in the end causes premature failure of the unit as a whole.  Other issues can cause short cycling--one example includes defective or overloaded start components.   

STRIP HEAT: A strip heater is a radiant, electric heater located in the air handler (indoor unit) of a heat pump. Since heat pumps function by extracting heat from outside air, they become useless in temperatures of 35 - 36 degrees (F) and lower. The strip heater then takes over. The blower in your air handler (which pushes conditioned air from the heat pump into your ductwork) also pushes the output of your strip heater into your home. Strip heaters are not as efficient as heat pumps, and you will incur higher electric bills during periods in the winter where the temperature stays close to (or below) freezing. The solution? A dual fuel system, which is combination of heat pump and gas furnace--the heat pump does its due dilligence for air conditioning and heat for temperatures above of 36-40 degrees, and the gas furnace serves as backup during colder times.

SUBCOOLYou will probably notice "subcool" measurements on your system checkups.  Subcooling is the companion to superheat, described below in the next definition.  These two components are considered by many to be the most complex concepts of HVAC!  To explain what this is, let's back up a step and identify the  basics components of a heat pump/AC system, which are the four componensts of any refrigeration cycle: compressor, condenser, restriction devise, and evaporator.  The four states of refrigerant are hot gas, hot liquid, cool liquid, cool gas.  "The process begins at the compressor. The refrigerant enters the compressor as a low-temperature gas that has been heated above its boiling point. The compressor pushes the gas out as a very hot vapor. The refrigerant flows to a condenser where the heat is removed by air or water flowing over the condenser coils. As it releases its heat, the refrigerant is cooled below its condensing or 'saturation' temperature and becomes a liquid. This is the sub-cooling. The sub-cooled, high-pressure liquid flows to a restriction device--either a capillary tube or thermal expansion valve (TXV). As the liquid flows through the restriction device, it changes from a high-pressure liquid to a low-pressure vapor/liquid mix. This low-pressure mix flows into the evaporator where it absorbs heat above its boiling point. This super heated gas then flows to the compressor to complete the circuit."

SUPERHEATYou may notice "superheat" measurements in the midst of notes for seasonal checkups.  Think of this as "compressor insurance."  Liquid refrigerant is turned into vapor while in the evaporator coil, and it is critical that this conversion happens completely--if liquid ends up going through to the compressor, it will cause significant damage over time.  "Superheat" is the amount of heat added to refrirgerant after it has already turned into vapor, added to ensure that the freon maintains itself as 100% vapor as it passes through the compressor.  It's a delicate balance, as too much superheat will not keep the compressor and its motor cool enough. Technicians always come armed have a chart to keep themselves straight on how much superheat is needed. 


THERMOCOUPLE: Located in your gas furnace, a thermocouple is often referred to as the pilot's "co-pilot,"  It senses heat from the pilot, and determines if there is enough to safely light your furnace.  If there isn't enough heat (as is the case when the pilot is out), the thermcouple will shut off gas flow.  If all is well, it keeps the main gas valve open.

TRANSFORMER:  HVAC systems typically have "primary" and "secondary" circuits and boards, which run at different currents & voltages.  A transformer converts voltage amounts between the primary and secondary circuits.  For example, it may "transform" voltage from 240 or 115V to 24V.  A bad transformer can cause either your indoor or outdoor unit motors not to run, along with your compressor.        

TXV VALVE: "TXV" stands for "thermal expansion valve."  It is a metering device that controls the amount of freon that passes into the evaporator coil.   It monitors the temperature of the condenser coil and controls the flow of freon to accomodate the requested temperature on your thermostat.  TXVs are a critical component in your HVAC system.  The refrigeration process is composed of four basic components--compressor, condenser, evaporator, and the metering device.   

UV LIGHT: UV lights were introduced into the HVAC market in the mid-90s. Like the sun, these special lights give off UV waves, which easily penetrate thin-walled cells or micro-organisms like germs, viruses and mold spores, leaving them unable to grow or multiply. As their effectiveness with destroying germs & bacteria became evident, they rapidly became regular components in the HVAC systems of hospitals and other medical facilities. From there they found there way into educational institutions. The price point of this technology has dramatically fallen in recent years, making it economical for residential applications. The UV light is positioned in your air handler (the inside unit of the HVAC system), and sit above your blower, effectively treating all the air being pushed into your home. In addition to killing mold, mildew, bacteria and other germs, UV lights have even proven to be effective in killing most household odors. Overall air quality is dramatically improved with the installation of a UV light in your home.

WET BULB: You may notice "wet bulb" measurements in the data on a service call or checkup ticket.  Wet bulb temperature is used in conjunction with "dry bulb" temperature to accurately determine relative humidity.  This is important in getting your HVAC system tuned properly.  As the name implies, "wet bulb" temperatures used to be determined be wrapping a standard thermometer in a wet cloth.  New technology has introduced tools that provide far more accurate wet bulb measurements.   Wet bulb temperatures will always be lower than dry bulb temperatures.  In the event of 100% humidity, the two measurements will be the same.    


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