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Greetings & salutations from the Comfort Crew of Comfort Heating & Cooling!  We are family-owned HVAC contractor based in Fredericksburg, VA.   Our goal with these blogs is to help educate homeowners about their HVAC systems–as with anything, knowledge is power.  Understanding your heating and air system will help you make wise decisions regarding maintenance and expenditures.

In this exciting episode, we are going to discuss an extremely important aspect to HVAC system repair and installation–pulling a vacuum.

To best explain this concept, let’s back up a step and cover some necessary HVAC 101 basics.  Imagine taking a glass of ice water outside on a steamy summer day.  You will notice condensation forming on the glass, correct?   Now imagine how much condensation would form if that ice water was negative 400 degrees Fahrenheit!

Flash Fact:  The Freon in your HVAC system is well BELOW negative 400 degrees Fahrenheit.

Condensation forms every time your unit’s copper lines are opened to the atmosphere.  New system installation obviously involves open copper lines, but numerous repairs also require opening the lines–examples include replacement of an evaporator coil or compressor.

Condensation in a HVAC system is verboten–a dangerous no-no that acts rather like a blood clot in your body.  It is absolutely crucial that this moisture be completely removed.  The method by which moisture (called “non-condensables”) is removed is via a vacuum pump.  As the name implies, these devices pull moisture out of the system.  Vacuum pumps measure their performance in units called “Microns.”  Every manufacturer of HVAC system has a set Micron level that must be achieved to ensure proper performance.

Pulling a vacuum also guarantees there are no leaks in the system.  Even a pinhole leak will prohibit pulling a vacuum to a certain level and holding at that level.  Rule of thumb for technicians that know there stuff–pulling a system down to 350 microns (and holding at that number) ensures that all non-condensables are out, and there are no leaks anywhere in the lines.

The problem for techs is time.  The time it takes to pull a proper vacuum is affected by a number of variables, the first of which is the application–new system installs require far less time to pull a good vacuum as opposed to a part replacement.  Other factors that effect time are: the size of the vacuum pump being used; the size/tonnage of the unit; the length of copper lines connecting indoor and outdoor units, and the amount of moisture in the system–higher humidity days will generate more moisture than dry days.  New system installations (and any repair requiring opening of the copper lines) should NEVER be done on misty or rainy days.  As an example of time–a small vacuum pump pulling down a large 5-ton unit with 75 foot copper lines on a high humidity day….pulling a good vacuum could easily require a full day, if not more!  To add to their woes, technicians can’t just leave the pump to do its thing and return later–part of the process involves routinely changing the vacuum pump’s oil.

In the heat of the summer technicians often get over-booked and can be forced to cut corners on their work.  The biggest time suck in this industry is pulling a good vacuum, so it is almost always the first area where quality suffers.

So what can happen with a badly pulled vacuum?   There’s a chance that nothing could happen–there’s a chance that a short vacuum time is enough to get moisture out, and assuming no leaks your system could be fine (albeit possibly running at less than peak performance).  Going back to the analogy that non-condensables are akin to blood clots in your body…a person with a blood clot could be fine for years and years with no issue.  There’s also a good chance the clot will hit a critical area, potentially causing tremendous harm–death is not beyond the realm of possibility.  It’s the same for your HVAC system–a system with moisture in the lines could run for weeks, months, even years with no issues (although performance will almost certainly be affected)…and this is the big problem with a badly pulled vacuum–you may not have a problem until well after the labor (and even parts) warranty has been exhausted.  Non-condensable damage isn’t easy to fix, and of course the repair could be a full system replacement.

How do you protect yourself?  Ask questions BEFORE technicians put their hands on your unit.  Ask “to what microns do you pull a vacuum?”  Remember–350 microns is the magic number to absolutely guarantee no leaks and removal of all moisture.  You want to hear AT LEAST 500 microns–this is usually enough to ensure no moisture, and an experienced tech will be good enough to install the unit with no leaks.  Make sure the technician actually owns a micron gauge (called a micrometer).  Many technicians feel they know when a system has been adequately pulled down, and that’s really impossible without a gauge–as mentioned before the number of time variables involved make every system different.

That’s all for today–we hope this has been useful!  For DIY tips and our “Diagnosis Dictionary,” visit our website at

Hello again from the Comfort Crew!

I have been writing blogs for the Comfort Crew for the past couple of years, and wanted to drop the 3rd-person narrative to share my personal experiences with my Daikin ductless mini-split system.

In case you aren’t aware of the technology, the ductless mini split system is a heat pump that, as its name implies, does not require any ductwork.  Rather than an air handler inside your home from which ductwork is connected, a ductless system has a wall-mounted unit that is a small air handler–air is conditioned and blown directly into the space in which it is installed.   The wall mounted units are around 30 inches long, 11 inches tall, and 8 inches deep.

Ductless systems utilize “inverter compressor” technology, which makes them extremely efficient.  What does this mean?  A standard compressor functions rather like a car that has a gas pedal which cannot be feathered–you would have two options–either floor the pedal or don’t have your foot on it at all.  Thus if you are trying to maintain 60 mph you would floor the gas to the desired speed, let of the gas, floor again to get back to speed, etc.  What ends up happening is you would go above and below the desired speed, and you would use a lot of gas.  That’s how a standard compressor functions to keep your desired temperature.  The inverter compressor functions like a normal gas pedal–it can feather its power to the desired temperature and hold as necessary.  This makes these units operate with a very high Seer rating, and overall power savings is immense.  One outdoor unit can control up to eight air handlers!

I live in a 1,000 sq. ft. bungalow, one level with unfinished attic and basement.  We have a floor grate oil furnace for heat and window units for air conditioning.  The options for a standard heat pump installation were limited, as there just isn’t any room for ductwork.  I finally decided on installing a Daikin ductless system, and we couldn’t be happier with the equipment!

We opted for two outdoor units, one on either side of the house.  Each controls two wall-mounted air handler units.  We could have gone with one 4-port system, but I didn’t want line sets (the copper lines that connect the indoor unit to the outdoor unit( wrapped all the way around the house.  We have air handlers in each of our two bedrooms, one in our living room and one in our kitchen (dining room sits between the living room and kitchen; a bathroom site between the two bedrooms and a small en suite bath comes off one of the bedrooms).  The setup has proven to perfectly condition the entire home.   Each air handler was installed above our windows–they only require about an inch  and a half clearance from the ceiling–while we could build a decorative valance around them, we don’t even notice that they are there.

The first  thing we noticed about our Daikin ductless system is the noise level–after listening to the jet plane noise of our oil furnace and the racket of our “window shakers,” the house became suddenly very, very quiet.   Try this–exhale while quietly whispering “wahhhhh.”   Both the indoor and outdoor units operate at about that level of noise.  They are virtually silent!

The second thing we noticed is that every square inch of our home had become comfortable–the floor grate furnace and window unit ACs were not able to condition the further reaches of our small home.  The areas around the units themselves would be extremely warm/cold, but the further corners of the home would be the opposite.  With the ductless systems, every room is a consistent, comfortable temperature.   These units keep airflow moving through the home even when it is not conditioning the air (utilizing fans that use less electricity than a light bulb).

The third thing we noticed was our power bill–it was either equal to or lower than what we were paying for systems that realistically only kept half our home comfortable!  The Daikin units have numerous power-saving features, such as an “econo mode” that’s perfect for keeping the home conditioned while on vacation; another setting is designed to slowly ramp down the cooling or heating while you are asleep at night, another neat option has an electric eye that recognizes movement in the room–if it senses there are people present it operates normally–if nobody is in the room it ramps down energy usage!

I could go on all day about these units, but let me just say that if you are considering a remodel or new construction and have limited space for ductwork (or if you just want a highly efficient system that’s virtually silent), consider the Dakin ductless.

For more info on the Daikin units, visit

Comfort Heating & Cooling  will be happy tom come out and do a free estimate and assist in weighing your options (in the Fredericksburg VA area).  Give us a call at 540-373-8471, or email us with any questions!   Be sure to check out our DIY HVAC tips at

Hello and welcome to Comfort Heating & Cooling’s blog o’ the month….the topic today is one we have preached on many times, and will keep on preaching till we run out of breath–filter changing. A couple of dollars will quite literally save you thousands of dollars.

We run a staggering number of service calls in which major, costly repairs are needed, along with calls where we find the customer has a dead unit….all because the homeowner did not invest in monthly filter changes. Two dollars a month is all it takes, and it’s so very critical.

Why? Your HVAC unit is a lot like your body–it needs air to function. Think of what happens when you can’t breathe (those with asthma will really know what this feels like). You get light-heated, your blood pressure rises…extended periods with little to no air will result in unconsciousness, even death. It’s the same with your HVAC system–it’s constantly pulling in air, and the dirtier your filters get the harder your system works to get the air it needs. The strain this places on all your components is tremendous. Give it enough time and motors start failing. Compressors burn out. Systems fail. Add to the mix the fact that a dirty filter will start allowing debris through to your system. If you follow the journey air takes through your system, you will find that air passes through your return air grill and the next stop if the evaporator coil in your air handler. This is the heart and soul of the indoor unit and it has thin, delicate fins. Allowing dirt on this coil would be like breathing in a pile of dirt–your lungs are the next stop in the journey through your body, and you definitely don’t want dirt in your lungs!

You don’t need a fancy filter. In fact some of the most expensive filters out there (those with such things as deodorizers) can actually act like a dirty filter. Just invest in cheap poly filters and change them AT LEAST every three months. Monthly is really ideal, particularly in homes with pets.

Invest a couple of dollars and save yourself thousands.

Want more tips on how to preserve your HVAC investment? Check out our website at

Sometimes when we get service tickets back from technicians, they are riddled with terms and technical jargon that are impossible to decipher.  With that in mind, we have created a “diagnosis dictionary” to assist you with some HVAC 101.   Visit us at anytime for help–entries and definitions are are being added frequently.  Here’s a copy of what we have so far–we hope this helps! 

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.

 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 steam rising from the top of the unit.     

 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 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 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. 

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.” 

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. 

MERV: MERV is a standard for rating the performance of filters.  Filter manufacturers all have different ways of rating their  products, so ASHRAE (Amercian Society of Heating, Refrigeration, and Air Conditioning Engineers) decided that a standardized rating system was needed so consumers could make educated decisions regarding filter purchases.  MERV ratings range from 1-16.  While it would be nice to state that the efficiency of filters increase with each MERV rating, it’s a statement that’s a bit deceiving.  MERV 1 filters can be just as efficient as MERV 16 filters–it’s what the filter is capturing that defines the MERV rating.  The rating is actually a measure of what types of particles a filter can caputure.  For example–MERV 1-4 filters capture larger particles such as pollen and dust spores; MERV 5-8 filters capture smaller particles, such as mold spores, hair spray chemicals, and cement dust.  MERV 18 filters capture the smallest partciles, such things as tobacco smoke and the nasties released from sneezes.  To throw a spanner in the works, consumers buying filters for typical residential applications need to be careful with higher MERV ratings.   A MERV 18 filter may capture about every particle out there, but the thickness of the filter can inhibit the performance of a heat pump, furnace, or AC–the higher MERV filters are designed for commercial systems with powerful blowers.  As a rule of thumb, do not exceed MERV 8 for residential systems.  Feel free to talk to one of our technicians for a recommendation on what MERV filter is best for your home.  Regardless of what filter you buy, remember this–the best filter in the world is worthless if it’s dirty.  Filters should be changed every three months–monthly for homes with a lot of pet hair or dust.  Think of a filter like a protective face mask–the more clogged it becomes, the harder it will be to breathe.  Take it a step further and think of what happens when you can’t breathe….your lungs struggle to capture air, your heart works harder to get air to the lungs, and your entire body can beome fatigued…unconsciousness can result, even death!   It’s no different for your HVAC system.  The harder your system works to get air across the coils, the more strain is placed on fan motors, compressors, etc.  Dirty filters also allow particles to pass through to your system, the first recipience being the evaporator coil in your air handler (indoor unit).  This of what would happen if you stood over a pile of dirt, dust, and pet hair….and proceeded to deeply breathe in these goodies.  Not good…the consequences to your health would be dire, and doing it for months at a time could really do some damage.  We recommend staying with MERV 8 and lower filters, and change them every 1-3 months.  Our mantra–“save money, change monthly.”       


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.

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. 

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.

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.   

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.    

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.  





You may have noticed subcool & superheat measurements on your HVAC systems’ seasonal checkup reports…so what are these?

Many consider these concepts to be the most complicated of the HVAC world…so we will try to convey this in as simple a way as possible. We found a good summary on The following article is by Norm Christopherson:

“The purpose of this article is to provide a simple explanation of these terms for those who desire a concise understanding as well as a review for those who understand the terms but want to take another look. An understanding of these terms and the concepts related to them is essential to understanding the air conditioning and refrigeration mechanical-refrigerant cycle as well as being necessary to troubleshooting problems.

Most materials can exist in three forms: solids, liquids, and gases. Water is a common example. Water can exist as a solid (ice), a liquid, or a gas or vapor (steam). Only a gas or vapor (these are interchangeable terms) can be superheated. Let’s use water as an example as we explain these terms.
Water at sea level boils at 212 degrees F. When heated to 212 degrees F, the molecules that make up water are moving at a high enough speed that they overcome the air pressure above the water. As additional heat is added to liquid water at 212 degrees, the water begins to boil. As the water boils it is changing state from a liquid to a gas. In addition, during the boiling process the temperature remains the same (212 degrees F). There is no change in temperature during a change of state.

This phenomenon is true for all substances as they change state no matter how much heat is added. As long as the water is still boiling and not all the water has completely changed to a gas (steam) the temperature remains at 212 degrees F. This means that a thermometer placed in boiling water will remain at 212 degrees throughout the boiling process even though heat is added to cause the water to boil. This heat of boiling is called latent heat. The word “latent” is a Latin word for “hidden.” The heat added to the water is hidden from the thermometer since the temperature remains unchanged during the boiling process.

After all the water has changed to a gas or vapor (steam), then the addition of still more heat to the vaporized water or steam will cause the temperature of the steam to increase above its boiling temperature of 212 degrees. Any increase in temperature of the steam above its boiling point is called “superheat.” Steam at 213 degrees F is superheated by 1 degree F.

Superheat is then any temperature of a gas above the boiling point for that liquid. When a refrigerant liquid boils at a low temperature of 40 degrees in a cooling coil and then the refrigerant gas increases in temperature, superheat has been added. If this refrigerant changed from a liquid to a gas or vapor at 40 degrees and then the refrigerant vapor increased in temperature to 50 degrees F, it has been superheated by 10 degrees.

We commonly think of boiling as always being accomplished by a liquid when it is hot. This is because we are familiar with boiling water. However, air conditioning and refrigeration systems use liquids (refrigerants) with much lower boiling points. If a liquid refrigerant boils at -10 degrees and is then warmed up to 0 degrees, it is then a superheated gas containing 10 degrees of superheat. Heating that same refrigerant gas to 10 degrees means that it now has been superheated by 20 degrees.

Lowering the pressure over a liquid lowers the boiling point. There is less pressure above the liquid to overcome. That is why water at the top of a mountain may boil at 190 degrees (depending upon the altitude) rather than at 212 degrees F. By controlling the pressure over a liquid, we can control the boiling temperature. That is why a service technician monitors the pressures in an air conditioning system. The technician is actually monitoring the pressures and temperatures where the refrigerant is changing state.

Saturation is simply the term used to describe the point where a change of state in a substance is taking place. For water at sea level, the boiling temperature is 212 degrees F. Therefore, we say the saturation (boiling temperature) is 212 degrees. As soon as the temperature of the steam is heated above its saturation temperature, it has been superheated.
Refrigerant that has boiled (turned into a vapor) at 40 degrees has a saturation temperature of 40 degrees. If the refrigerant vapor is heated to 41 degrees it is no longer saturated, it is then superheated by 1 degree. Remember, only a gas or vapor can be superheated. Superheat is any temperature of a gas or vapor above its saturation temperature.

Subcooling is now easy to understand. Only liquids and solids can be subcooled. Subcooling is any temperature of a liquid or solid below its saturation temperature. Let’s use water as an example again. Liquid water at sea level has a saturation (boiling) temperature of 212 degrees F. If we were to add heat to the saturated water, it would first boil away with no change in temperature (remember latent heat?) and then become superheated if still more heat were added to the vapor (steam) after it had all turned to a vapor.
Instead of boiling our 212 degree water by adding heat, we shall remove heat from the 212 degree water. As heat is removed from the liquid water, its temperature will drop below its boiling (saturation) temperature. Water at 211 degrees has been subcooled by 1 degree F. If the temperature of the water is decreased to 180 degrees, the water has been subcooled from 212 to 180 degrees. That is, it has been subcooled by 32 degrees. When you drink 180 degree coffee, you are drinking a subcooled liquid!

Sensible Heat And Latent Heat
Sensible heat is heat that can be measured by a thermometer. Anytime heat is added or removed from a substance and a temperature change occurs, a sensible heat change has taken place. Since both superheat and subcooling are changes in temperature, they are both sensible heat processes.
When an air conditioning system cools air, sensible heat has been removed. In fact, since the air is a gas or vapor and is heated far above its boiling (saturation) point, it is superheated air. Yes, you are breathing superheated air, as the air is hundreds of degrees above the temperature at which the gases which make up air would condense back into liquid form.

Superheated does not necessarily mean hot. And, subcooled does not necessarily mean cold. Superheat and subcooling are determined by the boiling temperature of the substance and, unlike water, many substances have low boiling temperatures.

Recalling that latent heat is the heat which is added to a liquid to cause it to change from a liquid to a gas (boiling) without a change in temperature, let’s go to the next step. When a gas or vapor is above its boiling point, it is said to be superheated. Cooling the gas removes its superheat. When all the superheat is removed from a gas, the gas will condense back into a liquid. The heat removed from a saturated gas to allow it to condense back into a liquid is once again latent or hidden heat and is not a sensible heat process. That is, during the process of changing from a gas to a liquid, it occurs at a constant temperature; therefore a thermometer will not detect any temperature change. That is latent heat.

Air contains water vapor or moisture. Too much moisture (humidity) in air is uncomfortable. As air containing too much moisture passes over a properly designed, installed, and operating air conditioning system, the air is cooled by the air conditioning coil (evaporator) located at the indoor blower section. If the air containing the moisture is cooled to the condensing temperature (dew point) of the moisture in the air, some of the moisture will condense and deposit on the coil and fins of the cooling coil. Since the water vapor is changing from a gas or vapor to a liquid, this is a latent heat process. The condensed water should run off the coil and be drained away.

A properly operating air conditioning system both cools (a sensible heat process) and dehumidifies (a latent heat process) the air. For example, given a 3-ton residential air conditioning system, a percentage of the total capacity of the system is utilized to cool the air while the remaining percentage of the total capacity is used to dehumidify the air. Properly controlling both the temperature (sensible heat) and the humidity (latent heat) will provide the optimum comfort for the occupants.

Measuring Heat
Latent heat cannot be directly measured as can sensible heat. In order to properly adjust, troubleshoot, and repair air conditioning equipment, it is necessary that we understand heat and how to measure heat.
Superheat and subcooling are both sensible heats and therefore can be measured with a thermometer. Superheat and subcooling are also temperature differentials. That is, each is the number of degrees a gas or liquid is above or below its saturation temperature. It is essential that a service technician be able to accurately measure these differentials and diagnose system operation from them.”

Norm Christopherson is a technical writer, seminar presenter, and former HVACR instructor. He is currently seeking training opportunities. He can be contacted at

Publication date: 01/12/2004

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Your HVAC system got you through the winter–is it ready for the summer?  Sprintime is the best time to get your heat pump or AC checked out.  Remember–just as your vehicle needs routine maintenance, so too does your HVAC system–particularly since it runs 24 hours a day, 365 days a year.  Imagine how much maintenance your car would need if it ran under those conditions! 

Make sure your filters are changed–it’s amazing how much damage can come from a dirty filter.  Changing your filters once a month will save you thousands of dollars in needless repairs, and ensure that your system runs to its full lifespan.  Check your outdoor unit and confirm that there is no debris (leaves, dirt, pet hair, etc.) clogging the coil.  The outdoor unit needs room to breathe–preferabley a foot of clearance from fencing or any other obstructions.

Check out for more DIY tips and info on a maintenance agreement! 



Here are a couple of tips to help keep the winter cold where it belongs–outside!

1) Keep curtains, drapes, and blinds closed. You would be amazed at how this simple tip will affect your utility bills. Windows are one of the bigest areas for heat loss in your home, so keepoing blindsand curtains closed will be a simple, cost-free, and efective energy saver.

2) Change you filters monthly–This is the most important DIY tip in the HVAC industry. Clogged filters not only cause higher utility bills, they put strain on your HVAC system, causing premature part failure. You don’t need anything fancy, the poly filters that run about a dollar will do the trick. In this case it’s quantity over quality…frequently changing cheap filters is far more effective than infrequently changing high-dollar filters.

3) When you arrange your furniture, make sure that all wall and floor grills have plenty of room to “breathe.” Allow about a foot of space aorund every filter so that they can effectively draw or expel air, depending on their function.

4) Keep outdoor unit free fo debris. Air is drawn into your home via the outdoor unit, and the contant air suction can cause the unit to become clogged with leaves, pet hair, etc. During warmer weather, it is OK to lightly spray the unit’s coil (make sure it isa LIGHT spray), and in colder temps carefully removes larger items such as leaves manually. The unit’s coil has delicate and exremely sharo fins, so use gloves and proceed with extreme caution.

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