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Residential Heating & Cooling

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. 

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.

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 BOARD:  As 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 SENSOR:  The 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 steam rising from the top of the unit.     

DRAIN PAN:  Located 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 moisture. 

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 DRIER: Located 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. 

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." 

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).  

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.

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. 

SUBCOOL:  You 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."

SUPERHEAT:  You 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.  

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.