Jim Johnson

Picking up where we left off last week, another factor to keep in mind about cabon monoxide generating equipment and draft measurements is that the water column-inch measurement scale we mentioned is a very fine measurement of pressure. One PSI is equal to 27.70 inches of water column, and the draft measurements we mentioned relative to a natural draft appliance are a fraction of a water column inch. The bottom line regarding the proper operation of atmospheric draft equipment such as a water heater or natural draft furnace is that if a given CFM of air is removed from the building due to the conditions mentioned above, then some method of allowing the re-entry of the same amount of air into the building must exist.

An important factor to understand about this situation is that it can be easily written off as extremely rare because the general belief is that if it did happen, somebody would be killed by the CO spill, or at least become gravely ill and wind up in the hospital. As I said last week though, there’s such a thing as low-level CO poisoning, which doesn’t always result in an emergency trip to the hospital. Here are some numbers for you to consider about CO levels in a building, measured in what is referred to as an ambient measurement in PPM (Parts Per Million):

009 PPM: Maximum allowable concentration for continuous 24-hour exposure. In an outdoor situation, this standard is often exceeded in urban areas due to auto exhaust.

10 to 35 PPM: Occupants should be advised of a potential health hazard, particularly to infants, small children, elderly people, and persons with respiratory or heart problems.

35 PPM: Common action level for fire department and other emergency personnel to use self-contained breathing apparatus.

50 PPM: OSHA requirement for maximum allowable concentration for workers continuous exposure in an 8-hour period.

70 PPM: Concentration required for UL2034 alarms to sound when CO at this level is present for as long as 60 minutes.

36 to 99 PPM: Medical alert. Ventilation required.

100 to 200 PPM: Dangerous, a commonly accepted building evacuation standard.

150 PPM: Concentration required for some UL2034 alarms to sound when CO at this level is present for 10 minutes.

220+ PPM: Extremely dangerous.

When you consider the listings above, you immediately recognize a possible health hazard for many people. Note that many alarms do not sound until the CO level in the building is beyond what is known to be a health hazard for the elderly, those with health issues, or children. A fundamental way to consider CO alarms is that they are designed to go off in the event that the carbon monoxide level in the building reaches a point where it would be hazardous for a healthy adult male….based on requirements that were initiated via testing and research involving military personnel.

Another factor to consider regarding a CO alarm is when it was purchased. For the most part, the sensor in the alarm that reacts to the carbon monoxide has a shelf life of approximately two years from the date of manufacture. And most consumers are not aware of this, thinking that if they faithfully replace the battery and press the TEST button on their five-year-old alarm, initiating an audible warning, that they will be protected against a CO spill. The simplest way to explain this process to a customer is that then they press the button, what they’re testing is a button and a power supply only, not the ability of the sensor to function. The only way to properly assess the function of a CO alarm is to use a test kit that includes a plastic bag to surround the alarm and an aerosol container of a material that, once sprayed into the isolated area, will cause the sensor to react.

The technician advising a customer about CO should also be aware of other facts related to the dangers of carbon monoxide. Symptoms are often written off as being other health issues, such as the flu. In one hospital study of 100 patients who requested treatment for what they thought was the flu, 24 were found to be affected by low-level carbon monoxide poisoning. Health care providers, if they are going to confirm carbon monoxide poisoning, must accomplish a carboxyhemoglobin test, which requires taking a blood sample for analysis.

Until next week…

Learn from yesterday….Live for today….Look forward to tomorrow


It’s a tradition in the appliance and HVACR service industry that there will be a high level of concern about carbon monoxide in the fall, with technicians fielding questions from the customers about alarms and requests for testing equipment for proper operation. And, as the winter wears on, people tend to forget about the concerns they had at the beginning of the season because their assumption is that the threat of a  (Carbon Monoxide, so identified with the chemical symbol “CO” since it is a product of carbon and oxygen) spill has been dealt with for another year, and they don’t need to be worried about it until the next heating season rolls around. The reason this is true is because most people equate a CO spill into a living space with a serious incident; the kind of thing you hear about on a news report about a furnace problem that results in someone getting killed.

However, from a technician’s perspective, there’s much more to the issue of CO safety, equipment operation and the alarms that are supposed to warn of an incident. One issue is what is commonly referred to as low-level carbon monoxide poisoning, which can be occurring in a residence or commercial building on an intermittent basis at any time of the year, and it goes largely unnoticed even though has an effect on the health of the building occupants. Consider the simplified building in Figure One.

Figure One

The first thing to understand about this building is that its tight construction, along with several other factors, is that it’s possible to create a slightly negative pressure in the structure. Hence, the collapsed look of the house. And, in this typical home, the gas furnace, which is a natural draft type, the and water heater  (which will almost certainly always be natural draft equipment), are in the basement along with the clothes dryer. On the main floor, there’s a range vent in the kitchen and a vent in the bathroom, and there’s a fireplace. And there is an attic vent system. Note what is happening to the vent system on the water heater and the furnace.

Both of these items, since they are connected to a common vent system, rely on a slightly negative pressure…likely in the range of -.02 to -.06 on water column-inch scale… to vent the by-products of combustion from the building. And when the pressure in the building is unaffected, or if there is either plenty of infiltration due to less-than-tight construction or a combustion relief system, this atmospheric vent system on these two appliances will operate as designed. However, in the event that the building pressure drops to a negative level, the vent system will back-draft, a condition we’re showing in our illustration.

One of the reasons for this condition is the vent on the clothes dryer, which expels approximately 150 CFM from the living space. Next is the kitchen vent, which, depending on the model, can send up to 250 CFM of air out of the building. In the bathroom on the second floor, the fan there, which is designed to vent moisture and odors, will also expel another 50 (or possibly more, depending on the design of the fan) CFM out of the building.

When you add the possibility that there could be infiltration from the living space up into the attic, and a possible open chimney damper on the fireplace, some, or all these factors, could create a negative pressure that allows for the back-drafting of any natural draft appliance. And, since carbon monoxide has a specific gravity of 0.98, meaning it is slightly lighter than air, an open basement door or infiltration from the basement to the living space will allow the CO to rise. And, since CO is so close to the weight of air, it will stratify and linger in the building.

Until next week….

Learn from yesterday….Live for today…..Look forward to tomorrow


“I used to do A/C work.”

“Yeah, I was in air conditioning for a while.”

“I went to HVAC school and worked at it some, but then I switched jobs.”

Have you ever been in a conversation with somebody who said something similar to the above? I have. And, I know that when I hear something like “I used to be in the HVACR business,” there’s a 99% chance that the person who is telling me that was never a member of a trade association nor did they ever invest any of their own time and money in learning more during the time they were ‘in the business’. And my reasoning behind that belief is simple. If a technical professional is serious (and I mean serious) about their craft, they will either become a member of an appropriate trade association and/or avail themselves of any opportunity for continuing education so they can take advantage of those available opportunities to continously improve, learn, and develop as the professional they are, even if it means investing some of their own money and attending training while they are “off the clock”.

And, it’s my opinion that if they aren’t serious about their craft, they won’t.

The unfortunate thing about the heating, air conditioning and refrigeration business is that, like any business, there are some people working within it who just consider what they do as a “job” and not a career. And all they focus on  is that whatever-amount-per-hour that they’re being paid while they watch the clock as closely as possible and keep score so  they’re sure they’re not ‘being screwed’ by “The Man” (whoever or whatever that really is).

Well, if you’re not of the ilk mentioned above, I have a suggestion for you. Join RSES. Yes, the price of membership is around $100 per year, but it’s money well-spent. As a member, you get a subscription to their monthly magazine, RSES Journal, which keeps you abreast of what’s new in the industry, and informed about the business you’ve chosen to be part of, while learning new things you need to know in order to stay up-to-date and hone your skills as an HVACR professional. And, you can stay connected with others in your craft by attending your local chapter’s monthly meeting. And, on top of all that, this trade association offers training (their motto is that they are “The HVACR Training Authority”) via workshops, conferences, and training materials in their on-line store. RSES is also active in providing preparation and study materials for NATE certifcation testing, and administering the exams.

To be sure, there are other trade associations related to the HVACR industry that also provide training opportunities and other benefits to HVAC contractors and business owners. In my opinion, though, RSES does the best job in regard to providing technical training for the people who are actually out there turning wrenches. And I recommend you make the very small investment in membership and avail yourself of the benefits being a member provides.

Unitl next week….

Learn from yesterday…..Live for today…..Look forward to tomorrow



In this troubleshooting situation we have a residential customer who has called for service, and their explanation of the problem is that their six-year-old gas furnace “won’t run.” They also tell the dispatcher that they have already replaced the thermostat, but it didn’t solve the problem.

When you arrive, you find the furnace sitting idle, and the customer explains that since they were able to determine that there was power to the furnace receptacle by plugging in a desk lamp, they assumed that the problem was with the thermostat.

Upon removing the access panels, and manually initiating the Interlock Switch, you locate the pictorial wiring diagram shown in Figure One, and get the following results with your voltmeter:

…0-Volts at COM and 24VAC on the Furnace Control

…115-Volts at L1 and N at the black and white transformer primary connections

Figure One


Here is your two-part troubleshooting question: Which component needs to be replaced in order to get this furnace operating again, and what steps do you take to ensure its proper operation?

Until next week…

Learn from yesterday…..Live for today…..Look forward to tomorrow


Note….this weeks’ blog segment was prompted by a phone call from someone who was trying to find out if our HVACR training DVD’s would work for him.

“Be sure you’re right, then go ahead.” For those of you who are old enough to remember the Disney TV series, or if you have visited Tennessee and studied some of the history there, you may recall that this quote was from Davy Crockett, who was known as “The Frontier Statesman” historically, and “King of the Wild Frontier”  according to Disney. Either way, the point of his statement was that, in any situation in which you’re trying to accomplish something or decide about something, what it always boils down to it that it is really just as simple as, well, being sure you’re right, then going ahead.

Personally, I rather like that philosophy, and Davy Crockett’s quote.

And, in the event we get one of the above-mentioned phone calls, it’s the philosophy I explain to someone who has been on our site, read about (and viewed a sample of) our DVD’s on refrigeration and electrical system troubleshooting and servicing, and they’re still not sure whether or not out stuff is what they need in order to either learn how to enter the field as an HVACR technician, or improve on their skills if they are already working in the heating and air conditioning industry.

It’s a good question…..and a fair one. And, like I said, employing the Davy Crockett philosophy is the best way to arrive at a decision.  And the best way to answer that question is to consider 10 other questions….the questions I ask someone who is trying to find out if our stuff is what they need. Here they are:

1. Have you read, and do you understand the title or titles of the program(s) you’re considering purchasing?

2. Have you read, and do you understand the description(s) and the content of the title or titles of the program(s) you are considering purchasing?

3. Did you view the video sample from one of our programs, and do you understand that what this sample does is show and explain our overall philosophy of presenting information in all of our productions, and demonstrates the quality of all of our productions relative to lighting, digital filming and audio? (Perhaps the real question here is  ‘do you trust us enough to accept that this is a fair question in the first place?’….but, I”m getting off track with that thought)

4. Have you noted what the run time is of the program or programs you’re considering purchasing? (I have to admit I’m always curious about this question. From my perspective, if I can explain something to you in 20 minutes, I don’t see why I should stretch it out into 40 minutes in order to make it look like the informaition is more valuable by extending the time frame of the program. It’s not how long a program is that determines its value to you, it’s the information you get out of it.)

5. Have you looked closely at the pictures of the DVD’s themselves and noted the copyright date so you know how ‘old’ our stuff is? (This is another question that I’m curious about. If you read about our training videos, you understand that there’s a lot of information there that we could have done a production on 20 years ago, and it wouldn’t be much different than it is today. Fundamentals are fundamentals, and will always be fundamentals. And, since the fundamentals, along with general troubleshooting procedures, are what we teach, the copyright date doesn’t, or, to put it more precisely, shouldn’t matter.)

6. Are you aware of the price of each individual program, and/or the price of any package or bundle you are considering purchasing? (I can’t resist commenting on this…..I think the way one should look at the price spent on education is not to be as concerned with the dollar amount as much as what kind of return there will be on the investment in the education…..for example, while you may spend $30 on a particular DVD program, the real question to consider is how many times are you going to get that $30 back because you learned the correct way to troubleshoot or test a particular component, and can replace it quickly and correctly, and get paid for doing so without having to take an inordinate amount of time or have the job result in a callback?)

7. Do you understand that some of our programs come with self-print CD’s that allow you to print a copy of the wiring diagrams and other resource material we use in the production so you can follow along and do what we do, and that’s the extent of our ‘interactive’ approach, and that some of our programs don’t have self-print CD’s along with the DVD’s because we don’t think it’s necessary to have them for every topic that we teach?

8. Have you taken the time to read all the information on our Frequently Asked Questions page, and do you understand all the answers to the questions?

9. Have you read the comments we’ve received from customers our Testimonials page?

10. Do you believe we didn’t make up the stuff on our Testimonials page?

If the answer to the above ten questions is yes, then a person who is considering buying our stuff has all the information that is available regarding our DVD’s. That’s it. As they say, that’s all there is, ’cause there ain’t no more. There’s nothing else to know. There just isn’t.

And, if a person has all the information that is available to them, then they are in one of two situations…..either they’re sure our stuff is for them, or they aren’t.

If they aren’t sure, perhaps it’s because they’re not really sure what they want. Maybe they know they need something, but they don’t know what it is. Or maybe what they’re really looking for is specific troubleshooting procedures regarding certain pieces of equipment, and they don’t realize that the information they need is only available from the manufacturer of the equipment. Whatever the reason for the uncertainty, it’s there. And if there’s any uncertainty there, then my recommendation would be to keep looking.

However, if the answer to all of the above questions is yes, and a person is sure that they can benefit from our stuff, then my recommendation is to do as Davy Crockett said, and go ahead.

Until next week…

Learn from yesterday…..Live for today……Look forward to tomorrow.





Appliance and HVACR service company owners and service managers all want their technicians to provide good customer service while they are accomplishing the troubleshooting/repair/maintenance tasks that are the technical side of their job. Here’s one approach you can take to create a culture of customer service in your business…

At your next regularly scheduled techncian…staff….associate, or however you refer to it meeting, hand out 3 x 5 index cards and explain that your entire customer service “policy” is going to be written on the cards.

Then, instruct everyone to write the following on one side of the card: Part One, Provide Outstanding Customer Service.

Next, instruct everyone to turn the card over and write the following on the other side of the card: Use Your Own Best Judgment In Any Situation.

Then….wait. And, yes, the silence will be deafening, but wait. What you’re waiting for is a ‘yabut’.

What’s a ‘yabut’? It’s a question that begins with a ….”yeah, but what if the customer says…..? or, “yeah, but what if what happens is….?

And, once the first ‘yabut’ comes up, all you have to do is say, “I want you to refer to Part One of our customer service policy.” And, when the second ‘yabut’ comes up, all you have to do is say, “Turn the card over.”

And, when the third ‘yabut’ comes up, say, “Turn the card over,” again.

And, when the fourth, or fifth, or however many ‘yabuts’ come up, you….well, you get the idea. After a while, the concept will sink in. What you want to convey about your customer service philosophy is that, while it might not be easy to accompish, it is, in fact, simple.

(Note….during a workshop where I recently presented this idea to a group of approximately 40 service company owners, service managers, and soon-to-be service managers, I was roundly (and a bit loudly) criticized by one of the attendees because, in his opinion, this idea was “so vague.” And, as always happens during a workshop attended by a group of people who are in management and supervision, I personally didn’t have to explain why this idea is effective. Another attendee spoke up and said, “If you can’t trust your employees to handle this, then you shouldn’t have hired them.” I couldn’t have said it better myself.)

Another benefit of going through this exercise is that it will help you identify where there may be any negative influences in your organization. The first technician who says something along the line of “I don’t get paid to make those kinds of decisions,” or “Are you saying you want us to do your job for you?” is in need of some coaching from you.

No, you’re not asking some one to do your job for you. You’re explaining to them that you want them to keep part one of your “policy” (Provide Outstanding Customer Service) in their mind at all times when they delivering the services that your company provides, and, that in some cases, part two of your “policy” (Use Your Own Best Judgement In Any Situation) will be something they can, more often than not, handle on their own, while sometimes, implementing part two will mean that their judgment will be that they need to call you for direction on what specific action to take…..that is, after they’ve explained the details of the situation to you and offered their opinion on what they think is the right thing to do.

To put it simply, what you want to convey to your people is that they are empowered to do their job, and that you are always there to provide direction… when necessary.

Until next week….

Learn from yesterday….Live for today….Look foward to tomorrow.





The 2012 Marcone Servicers Association convention, held last week in Las Vegas, was attended in record numbers by independent servicers…..mostly from the major appliance industry, along with some who also do HVACR. And, as it  always is with a trade association event such as this one, I have the opportunity to meet with people who either own and operate, or are employed by, a small or large company engaged in the business of either repairing major appliances and/or heating and air conditioning equipment. And one thing I never hear from anybody who has invested the time, energy and money to attend a trade association event is that they made a mistake in doing so.

So, here’s the first of those strong opinions….remember, I warned you.

If you’re running a one-person service operation, or if your company is considered “large”, or if you’re employed as a technician by a large or small company, it’s imperative that you belong to a trade association and, whenever possible, attend their convention or other events. I’ve had conversations with servicers who tell me that they “just can’t afford” to be a trade association member and participate in the events that are offered, but I’m convinced they’re wrong. One-Hundred and Eighty-Degrees wrong.

The reality is, when you consider that you can attend technical training sessions offererd by manufacturers, meet with your peers in your chosen business/craft/career to share information and learn from each other, attend sessions that give you an opportunity to get fresh ideas on customer service, business management, or supervisory skills, and find out what’s new and improved in the area of test instruments, equipment, and other tools to help you in your business, you “can’t afford” not to belong to a trade association and participate.

(On a side note regarding the major appliance service industry, I am often asked which trade association a servicer should join, either USA, PSA, or MSA, and my answer is always the same….yes.)

Moving on…..more strong opinions.

Since I’m in the training business and simply will not keep my opinions to myself, some of the conversations I often have at conventions are with employers about in-house training and what they provide in the regard to the technicians employed by their company. And (give ’em credit for honesty here), sometimes, the information I get from an employer is that they don’t have an ongoing, proactive program that allows them to contribute to the continued growth and development of employees. And, that’s another group of people who are wrong because they either don’t think they should do so, or are unable to do so.

In-house training sessions…..and, yes, it’s a meeting that is conducted during the day, meaning hourly people get paid to be there….that provide information on both the technical and soft skills side of the service business are the responsibility of the employer. If you’re the only one available to conduct such a training session, and you’re not sure how to proceed, go to Amazon.com and get a book on how to be an effective presenter, or attend a one-day seminar that’s offered by companies like Fred Pryor or Career Track on how to conduct effective meetings and be a presenter. And find a way to tap into the resources that are all around you, such as in the form of manufacturer’s service manuals, or getting in touch with a factory representative for help and information so a training session can be presented on electrical troubleshooting or other technical topic.

As the Nike people used to say….Just Do It.

Moving on….another strong opinion.

Again, on the subject of training and staying up-to-date in the service business; this time referring to technicians themselves. In addition to talking with employers at conventions, I also have conversations with technicians on this subject, and, believe it or not, some of them tell me that if they are paid hourly, and their employer wants them to attend a training session that may be offered on an evening, or other time that isn’t “on the clock” (or gets in the way of their earning time if they are paid on commission), then they should be paid for being there.

Oh, C”mon here! What kind of negative, scorekeeping, us-versus-them attitude is that!?

As I said above, a service company owner certainly has the obligation to contribute to the ongoing growth and development of the people they employ, but that doesn’t, for cryin’-out-loud, absolve a professional from their responsibility to invest in their career and also contribute to their ability to do their job as well as possible!

OK….OK…..I’ll calm down and wind this up. I’ve made my point on that sore subject.

The bottom line is that, in my opinion, an effectively run trade association, along with their conventions and other services and opportunities they offer to those of us who have chosen a career in the appliance or HVACR service  industry, are not an expense, they’re an investment. An investment that always pays off in more ways than one.

Until next week….

Learn from yesterday….Live for today…..Look forward to tomorrow.



When a homeowner or business calls for a plumber, electrician, HVACR, or appliance technician, who is it that actually shows up at their door to provide the service they requested?

Often, a customer isn’t really certain what the answer to the above question is because they’re not completely familiar with the way the service business works. When they do some research and place the call, they may be requesting service from a local independent operator, or they may be calling an area office of a large chain. In either case, the person who shows up may be someone who is considered to be a journeyman in their craft, having been tested and licensed as an individual….or they may not be.

In some states, for example, a service organization can have only one person on staff who holds the required license, and as long as that person’s name appears on the invoice issued to the customer, any other person employed by the company can perform the service. That means that the person who shows up at the door to clean the drain, intall the new air-conditioning system, or repair the dishwasher may actually be the person who has been deemed qualified via whatever licensing process applies, or they may be an employee of the company who does not hold an individual license.

From the consumers perspective, all this means is that they should always remember to ask questions. Ask about how the licensing that a particular company advertises actually applies regarding the technician who is going to show up. And, be educated about the issue of “licensing” and “certification”, and ask questions about that process. Certifications can, in some cases be required, such as EPA certification for a refrigeration technician, or they may be granted via a trade association. Like I said….ask.

A technician who isn’t “licensed” by a state entity such as a registrar of contractors, may in fact be “certified” by a non-government entity. And, having been through a certification process, may be eminently qualified to do the work that needs to be accomplished. Then again, a technician who is “licensed” by a state entity may not, in fact, be as competent as necessary to effectively perform the work.

In some states, not only are service company owners licensed, but each technician requires a license to be allowed to work. And, they may be required to document that they have completed a given number of hours in continuing education every year in order to be allowed to renew that license. And, that’s all well and good….except for the fact that the continuing education process may be, well, pretty much a joke. If a technician is just showing up for an 8-hour class, having picked the simplest thing possible from an approved list, and if the main focus of the entity providing the “training” is revenue, then all that has occurred is that the technician has, as we say, filled-in-a-square, and winds up with a renewed license.

What’s a consumer to do? Ask. Ask for an explanation of how a technician becomes licensed or certified, and ask about the continuing education process that allows them to keep that license or certification. Perhaps your state doesn’t even have a technician licensing program, but the company you are calling has an effective in-house training program and has embraced an industry certification process. Or perhaps the person who actually shows up at the door isn’t licensed or certified at all, but has been “unofficially” trained and has been in the field for many years, knows the particular equipment that needs to be repaired or the situation that needs to be handled ‘upside down, inside out and backwards’, and can do what needs to be done in an efficient and professional manner.

How would you know? Ask.

Until next week….

Learn from yesterday….Live for today…..Look forward to tomorrow.


Troubleshooting. It’s what we do as an HVACR technician. And, when it comes to troubleshooting, there are some simple steps to understand about the process. Here’s one way to get to what we understand is the bottom line about our job…..figure out what’s wrong, fix it, and get paid.

First, what is the specific type of equipment?

Second, what is the customer’s description of the problem? (Don’t write this one off because the customer isn’t a technician. People are familiar with the sounds, feel, and performance of their HVACR system.)

Third, what kind of history is there regarding repairs on this equipment? Who has worked on it before? What did they do?

Fourth, what is the sequence of operation when this equipment is working properly?

Fifth, what are the symptoms you encounter when you evaluate the operation of the equipment?

Sixth, what specific troubleshooting information is available from the manfacturer regarding this particular piece of equipment?….fault codes?….wiring diagrams?….step by step diagnostic procedures….service bulletins?

And, while you consider the steps above, determine the correct answer to the following problem:

The equipment is a 240-volt, single-phase split system heat pump, and the customer’s complaint is that there is “no cooling.” They also tell the dispatcher that they had the same problem at the beginning of the cooling season last year, at which time a part was replaced and the unit operated OK until now. When you arrive, you find that while the indoor and outdoor fan motors are operating normally, the root of the problem is that the compressor is attempting to start, but kicks off on its overload. When you remove the access panel, you check the schematic, and note the wiring configuration for this compressor, shown below in Figure One.

Figure One


However, when you survey the equipment, expecting to find the two run capacitors (Ca and Cb) wired in parallel (meaning that their value would be added to provide the proper PSC circuit for the operation of the compressor while only the Ca capacitor would be used in the off cycle to provide a trickle circuit through the start winding), you discover that the wiring has been modified and the compressor circuit now only employs one run capacitor as shown below in Figure Two.

Figure Two


What is the specific cause of this compressor’s failure to start, and what do you need to do in order to get this unit operating again?

Until next week,

Learn from yesterday…..Live for today…..Look forward to tomorrow.








When taking a simple and direct approach to understanding the fundamentals of HVACR, a technician evaluating the operation of a comfort cooling system needs to understand the operation of the refrigeration and air flow systems in the equipment individually and collectively. They are considered as being in balance with one another, simply because it’s universally understood that a refrigeration system cannot accomplish heat transfer at optimum efficiency without the proper amount of air flow throughout the ductwork, and the air handling system cannot provide maximum comfort if the refrigeration system isn’t operating as designed.

In Figure One, the TXV, DX system shown is accomplishing the maximum level of heat transfer possible.


Figure One


Consider first that the metering device in this system is capable of delivering the proper volume of refrigerant to the evaporator coil due to the synchronicity of the three pressures in the valve (evaporator pressure, spring pressure and bulb pressure), and, second, because of the correct volume and velocity of air flow through the coil. Note that the saturation temperature of the refrigerant is 38-degrees, and that the temperature drop through the coil is 20-degrees. And, we can also see that the evaporator superheat in this system is 12-degrees when we consider the last point of liquid in the 38-degree coil, and the 50-degree temperature reading at a point on the suction line directly ahead of the TXV sensing bulb.

Figure Two shows an example of the air handling system that makes the temperatures above achievable.


Figure Two


The first factor we want to mention regarding this illustration is that the equipment capacity is 3 tons, due to the application of the fundamental rule that an efficient system will operate with an air flow of 400 CFM per ton. (The total air flow shown in the return ductwork and the supply plenum is 1200 CFM.)

Note also the reduction of the supply plenum after the first four supply registers of 100 CFM each are served; then again after the next set of registers, which involves three at 100 CFM each and the bathroom registers at 50 CFM each, and then the third reduction in plenum size at the final segment of the supply duct system. This design of the supply ductwork, along with the turning vanes, allows the air handling system to operate with minimum noise and the necessary velocity required for proper throw from the supply registers into each room in the building. And, it also ensures that the static pressure in the system will be correct.

The factors to consider here are the slightly negative -0.03 WC (Water-Column-Inch) pressure in the return system, which allows for the free flow of air through the return, and the fan static pressure of 0.4, which is achieved due to the -.02 pressure at the fan inlet and the 0.2 pressure at the fan outlet. The proper static pressure in this system is achieved through the application of a manufacturer’s table for airflow characteristics, such as the one shown in Figure Three.


Figure Three


This table shows that the indoor fan has a maximum capacity of 1360 CFM while operating against a 0.4 static pressure, which means that the blower will easily achieve the required 1200 CFM for our three-ton system.

With the duct system and blower allowing for the proper return and delivery of air throughout the building, the balance between it, and the refrigeration system, will be achieved, resulting in the proper operation of the equipment from a fundamental perspective.

Until next week…

Learn from yesterday…..Live for today…..Look forward to tomorrow


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