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Preparing for the NATE Exam Excerpt


An E-Book By Jim Johnson

A Condensed, To-The-Point Approach To Passing A NATE Certification Exam



It’s been many years ago, but I’ll never forget it. A service industry was trying to get a technician certification program up and running. In the midst of all the brough-ha-ha about it, the association that had developed the certification testing program made wonderful predictions of the tremendous success of their initiative. I, on the other hand (though I’m usually optimistic about things), had predicted that the program would fail miserably. I was right. The association that spent a huge amount of money, and invested a great deal of time and other resources in the development of the exams, wound up selling the program for $1 to a trade association in the same industry who thought they might make a go of it. They didn’t. The program died, and never came back to life.

Why was I so sure that it wouldn’t work? Actually, there were two key components to my reasoning. First and foremost, the only thing they had to offer were the exams themselves, (no recommended study materials or opportunity for preparation) and they expected technicians to show up with bells on to take them. They announced the date that they were going to launch the program, and later said that they had a large number of technicians who had committed to take the exams. When I heard the numbers they were bandying about, I said some things that most people didn’t like to hear…that on that particular day that the exams were scheduled, although many people had committed to taking them, there would be more sick kids, broken-down vehicles, dying grandmothers, etc.. than you could shake a stick at on that particular day…and that’s exactly what happened.

The bottom line was that the technicians, who were supposed to take the exams, were, like many people who work in the service and repair of equipment, good at what they did, and knowing what to do. What they didn’t have was a confidence that they knew why something should be done, or the fundamental theories of electricity, refrigeration, and mechanical concepts that applied to their work. Of course, they didn’t want to be portrayed as somebody who didn’t know what they were doing because they failed a written exam, so, in large numbers, they didn’t show up, even though they promised they would.

The second component to my reasoning is best explained by relating a conversation I had with a group of about 50 technicians (I was facilitating a training session at a national convention) in the midst of this certification initiative, and I asked them a question: “When are you going to get certified?”

Their answer was simple: “When customers start to ask for it.”

After getting that answer, I went directly to the trade association president and asked him when they were going to let the public know that they should be asking about a technician’s certifications before agreeing to book a service call. His response was, “When we have a large enough group of technicians who are certified.”

Hmmm….ever heard of the term “Catch-22”? It’s a term that has been used in the Air Force to describe the situation in which a pilot needs to be psychologically stable in order to be allowed to fly, but, the general opinion is that people have to be a little nuts to want to fly certain missions in the first place, so they can’t let him fly because he’s not nuts…or, maybe not nuts enough…or something like that. At any rate, the trade association was waiting until they had enough certified technicians before launching an advertising campaign to educate consumers about the benefits of having a certified technician do their repair work, and the people who were supposed to make up the group of available certified technicians were waiting until the consumers (who had no clue that they were supposed to ask) asked about technician certification. Like I said, Catch-22.

The bottom line with NATE certification is that neither of the two issues that caused the collapse of that technician certification initiative applies to its certification program. There are many opportunities (this e-book is one of them) for technicians to prepare for taking the certification exam, and NATE does offer the consumer the opportunity (via advertising and a Web site) to become educated on technician certification and the fact that they should be asking for it. So, no, NATE isn’t going to die. It will continue to grow. Consumers will be more aware about asking about it. Manufacturers will require dealers to have a given number of NATE certified technicians on board in order to sell and install their equipment, and NATE certification will become an issue relative to state licensing of contractors. That’s the reality of NATE certification.

On to some myths and misperceptions on the subject of certification….

If you were to ask anyone from the general public what they think when they see that a technician is certified, or that a business employs certified technicians, you would, with continued probing for information, likely hear from them that they believe some sort of government agency regulates the certification process of said technicians. And, of course, they would be wrong about 90% of the time. Sure, there are some specialty technician certifications that are overseen by some sort of “Big Brother” agency, be it a federal, state, county or city government, but they are not in the majority. For the most part (NATE included) the government doesn’t get involved in the requirements set down for certification testing. It’s left up to the industry (who better would know what the professionals working in a particular industry should know in order to be certified?) to determine what competencies must be demonstrated in order to be awarded certification.

Here’s one example…..AWS, the American Welding Society, has been certifying welders for decades. If you’re a welder and you want to get a job doing pipe, structural, or any other type of welding, when you apply for the job there is always one question asked….”Do you have your AWS cert?”

And there never has been so much as one bureaucrat involved in setting the standards for welder certification. AWS was born when a small group of professionals in the welding industry decided that a certification initiative was necessary, and welds are x-rayed to make sure they’re done properly before a welder can be certified in a given skill.

How about this one…? ASE, Automotive Service Excellence. Formerly known as NIASE, the National Institute for Automotive Service Excellence, this organization certifies technicians in specialty areas such as brakes or alignment, among other disciplines within the automotive service industry. And which government agency is that oversees the setting of standard for these certifications? None. Those ASE-Certified signs you see in independent garages and car dealers around the United States are the result of an industry, and only the industry, creating and implementing its own technician certification program. Again, though, from a consumer perspective, the underlying idea that somebody, somewhere in a conference room or office in Washington D.C. regulates what goes on with automotive technicians and their being certified, is likely what you could easily get people to accept.

But there’s a reality amid the consumer’s misperceptions about the term “Certified”. It gives them a feeling of confidence. That’s why some HVACR and major appliance service contractors have “Certified Technicians” painted on the side of their service vans even if it only means that the technicians who service equipment are EPA certified in refrigerant handling procedures. And, c’mon, anybody who works in the refrigeration industry knows that anybody who wants to study for a while about rules and regulations relative to Section 608 of the Clean Air Act, recall some specific dates when certain laws when into effect, and, OK, be able to answer a few questions about the fundamentals of a refrigeration system, can pass an EPA certification exam segment, by answering more than 17 out of 25 multiple-choice questions correctly. But that doesn’t change the fact that it makes consumers feel better about buying service from a company that lists their technicians as certified. They still do.

Beyond that perceived reality, though is another more “realistic” reality. NATE certification is a process that enhances a technician’s confidence and competence. The facts cannot be denied. A NATE certified technician experiences fewer callbacks. And in the end, that’s a win/win/win/win….a win for the consumers because they get quality work, a win for the HVACR sales and service organization because their expenses go down, a win for the technician because when expenses go down that means there are more resources that can be channeled into a technician’s earnings, and win for the HVACR industry because as the standards are raised, the industry itself has more credibility, which will attract the much-needed new blood that will allow it to grow and prosper….and that’s exactly what I want this book to help you do as you prepare for your NATE certification exams.




When a technician is pursuing NATE certification, the first step is to accomplish a core exam. Core exams in either the area of service or installation evaluate a technicians understanding of the fundamental concepts applied to HVAC/R equipment servicing (relative to refrigeration and electricity), as well as safety issues, an understanding of tools, and soft skills. All of which makes sense. After all, how can a technician perform effectively relative to comfort cooling, for example, without a firm understanding of the fundamentals of temperature and humidity measurement, how a refrigeration system works in conjunction with an airflow system, and how the basic sciences apply to the proper operation of a system? It’s the same as building a house. Without the proper foundation, you won’t have much of a building. And so it goes with demonstrating proficiency in heat pumps, gas heat equipment or airflow systems. (For a listing of the specific NATE categories of certification, see Part One)

Without the proper foundation of understanding, you can’t be as effective as possible when troubleshooting and servicing comfort cooling, heating, or refrigeration systems. Some of the stuff a technician needs to know about core subjects is very straightforward, such as terms we should be familiar with when working in the HVAC/R industry. For example:

Sensible Heat: Heat that can be measured and felt.

Dry Bulb Thermometer: A temperature-measuring device used to measure sensible heat.

Latent Heat: Often referred to as “hidden heat”, it cannot be felt or measured, occurring during a phase change of a solid to a liquid, liquid to a vapor, or vice versa.

BTU: British Thermal Unit, the amount of heat it takes to raise the temperature of one pound of water one degree Fahrenheit.

Hmmm…seems pretty straightforward, doesn’t it? While the average person on the street would probably give you a puzzled look if you asked them to explain any of these simple terms, 99.9 percent of HVAC/R technicians would likely be able to recite the formal definitions we’ve listed here, as well as provide an explanation as to how they fit into the concept of heat transfer. And, beyond that “foundation” stuff, there’s the issue of actually paying the rent with that basic understanding.

What do I mean by “paying the rent”? Well (get ready, here comes an opinionated point-of-view), what I mean by that is that it’s nice to know stuff, but it isn’t worth much if you can’t find a way to pay the rent with it: put it into practical applications and accomplish some goal. In this case, the goal and the practical application are to be able to answer a test question relative to these fundamental terms. And I mean answer it. Not just by memorizing some information, then regurgitating at the appropriate time to choose A, B, C or D, but being able to understand the concept so you can figure out what the correct answer would be to any question relative to that concept. For example, take a look at the drawing in 2-1.

First, note our thermometer illustrations that represent temperature. There are two showing 32-degrees and one showing zero. Note also that we’re using two of the specific terms we mentioned above, sensible and latent heat. We’ve also added the idea of change of state to make out point. And, it’s clear that our discussion on this concept is going to apply to the idea of removing heat from a given quantity of water and causing it to change in state from water to ice.

Beginning at the left of our illustration, you could assign any temperature you wish, and you could also use any given quantity of water you want. For the sake of discussion, let’s say that we’ll be using one pound of water at 70-degrees F. With that understood (and recalling the definition of the term BTU) we could determine exactly how much heat would need to be removed in order to chill the water from 70 down to 32.

So, if our question was:

In the accompanying illustration, how many BTU’s of heat would be removed from one pound of water being chilled from 70-degrees F, down to 32-degrees F?

A. 40
B. 32
C. 38
D. 70

What was your choice? How did you arrive at your answer?

If you chose “C” you were correct. And, if you arrived at that answer by recalling that the definition of the BTU is “the amount of heat it takes to raise the temperature of one pound of water one degree Fahrenheit”, then applied that information to the concept of removing heat rather than adding, and then did some simple math—the difference between 70 and 32 is 38—then you answered the question by understanding a concept and being able to apply your ability to reason.

And what if you understood the concepts we’ve been discussing, and your question (refer to Figure 2-2) was:

The type of heat that must be added or removed to cause a change in the physical state of a substance is:

A. Specific Heat
B. Superheat
C. Latent Heat
D. Sensible Heat

Which answer would you choose? It’s “C” again, because the concept we’ve illustrated clearly shows that the change in the physical state of a substance (when water is in the process of becoming ice in this case), the type of heat being removed is latent heat. When you’re at the “beginning” of 32, your substance is a liquid. During 32, your substance changes in state from a liquid to a solid and you now have ice, once you reach the “end” of 32. Hence the definition of latent heat is “heat that brings about a change in state, but not a change in temperature”.

Now, referring again to Figure 2-2, on to your third question:

When one pound of ice is chilled down from 32 to zero degrees F, what type of heat is being removed?

A. Sensible Heat
B. Latent Heat
C. Superheat
D. Specific Heat

What did you choose this time? If you picked “A,” you were correct. Clearly, the latent heat process has been accomplished, and the numbers in our question illustrated a measurable drop in temperature, which means sensible heat—heat that can be measured—is the correct answer.

By the way, did you notice that in this question, there was some information that didn’t really need to be there? The “one pound of ice” reference could be deleted from the question and it wouldn’t affect the answer. The concept that needed to be understood didn’t concern the amount of heat being removed, only the type if heat. Now, if the question read…

How many BTU’s of heat are removed when one pound of ice is chilled down from 32 to zero-degrees F?

A. 32
B. 16
C. 64
D. 48

…there’s another concept that needs to be understood, which is referred to as the specific heat capacity of a substance. In the case of water in the first question we presented the answer was straightforward because the specific heat capacity of water is 1. However, to get the answer correct about ice, you would have to understand the concept of the specific heat capacity of a substance changing in the event of a change in state. The specific heat capacity of ice is .5, which means that the correct answer to our question would be “B”, which we would arrive at by again doing simple math as we did in the first question.




So far in the electrical segments we’ve presented, we’ve covered the fundamental principles that technicians need to understand, along with some basic stuff about specific components—motors, relays, etc. In this segment, we’re moving on to wiring diagrams. And, as you would expect in this day and age, when we say wiring diagrams, we also mean printed circuit board control systems.

The steps to understanding current wiring diagrams are the same as they were when HVAC/R equipment was made of electromechanical systems.

Step one: understand that the schematic diagram is a “map” of the equipment’s electrical circuits and components, and that the intent of the diagram is to simplify and explain the overall operation of a system. To understand schematic diagrams and electronic control systems (and being able to answer questions about them), you must understand specific types of equipment, such as the gas furnace example shown in Figure 10-1.

To interpret this diagram, first locate the symbol for the transformer. It’s located at the center of our illustration and it forms the basis for the entire diagram. Once the symbol is presented, all that needs to be done is to add “tails” to it to form the overall pattern that allows for the addition of specific component symbols. For example, the four-speed blower motor identified as BLWM, the Hot Surface Igniter (HIS), and Induced Draft Motor (IDM).

And, when considering the blower motor circuit, you’ll note the normally open contacts shown as BLWR, and also the normally open and normally closed set shown as LO/HI. The idea to nail down here is that a schematic diagram, whether it is depicting an electronic or electromechanical control system, provides you with a line-by-line description of the switching contacts that are wired in series with the load they control. Consider the Hot Surface Igniter (HSI) and the HSIR contacts that, when closed, will provide a complete circuit to the HSI. Note also that the Induced Draft Motor (IDM) won’t operate until the contacts of IDR are closed and allowing a complete circuit though the load identified as IDM.

With the operating voltage (if you want, refer to it as the “high voltage”) segment of the schematic understood, you can move on to the control (or “low,” if you prefer) side of the diagram to clarify the basic schematic point-of-view, which is…whenever you see a set of contacts wired in series with an operating voltage load, there has to be some method on the control side of the system to cause a movement in those contacts.

When evaluating schematic diagrams, always look for this correlation between the operating and control sections. For example, consider again the BLWR contact points shown near the top of the illustration. Where else do you see the identifier BLWR? The answer, of course is on the control segment of the diagram, and it’s presented inside of a circle, which is “schematicspeak” for Coil. (Don’t bother to look up the term “schematicspeak.” We made it up.)

Taking this simple approach to schematic diagrams would mean you would be able to complete the following statement:

When the CPU provides a 24-volt circuit to the BLWR Coil:

A) The normally open BLWR contacts will close.
B) The normally closed BLWR contacts will open.
C) The blower motor should operate on medium-low speed.
D) Both A and C.

The correct answer is “D,” which is simply determined by examining the schematic from the control/operating correlation perspective. Certainly, when 24-volts is applied to the BLWR coil, the contacts close. Also shown on the operating side of the diagram is another set of contact points (in the LO/HI Fan Speed Relay) that are normally closed. And, since the statement didn’t address anything regarding energizing the LO/HI coil shown on the control side of the diagram, we known that the normally closed contacts will remain just that…closed, which means that there will be a complete circuit to the medium-low speed of the blower motor. And this brings us to rule #2 of understanding schematic diagrams and answering questions about them:

Step two: always trace a circuit from source to source.

Certainly, in the “good old days” of electromechanical stuff, this was easy because the diagram clearly showed the either open or closed contact points on both the operating load and the control circuitry. Well, it’s still not too complicated in the world of solid state control systems when you consider the idea that a printed circuit board or CPU (meaning microprocessor and control circuitry—Central Processing Unit, in this case) is really nothing more than an assembly into which power is introduced, and at the appropriate time, is allowed to provide a complete circuit to whatever coil it is supposed to be energizing at the moment.

Note that when locating the “C” on the control wiring connections at the bottom left of the diagram, you’ll see a connection for “one side of the line” to each of the coils shown just above the CPU. Note also that there is a direct connection from the “R” control wiring terminal connection to the CPU.

OK…so it’s pretty simple. One side of the line “C” is wired directly to the control coils in this system. The “other side of the line” in the 24-volt power supply is wired into the CPU. And, at the appropriate time, on a call for heat, and once the heating cycle is in process, the CPU will allow power to the BLWR coil, which, in turn, allows the complete circuit to the blower motor.

And now, the next step in evaluating wiring diagrams…

Step three: understand what the sequence of operation is supposed to be.

We’ll look further into this step in our next segment. In the meantime, consider the following:

If, when reading 120 VAC at the PR1 and PR2 terminal connections and 0 VAC at the SEC-1 and SEC-2, you have determined:

A) The control transformer has failed.
B) The ILK (Interlock Switch is open.
C) The CPU has failed.
D) A limit switch has opened.

We’ll discuss the answer to this question in the Part Eleven.




Note….the correct answer to the final question in Part 20 is “A”.


In our last segment, our focus was on some of the electrical fundamental processes technicians need to understand to be successful in becoming NATE certified on gas furnaces. In addition to the electrical side of gas furnace maintenance, troubleshooting and repair, technicians also need to know about the fundamental process of combustion systems related to servicing this type of equipment. To begin, we’ll present a simple approach to the idea of combustion, that it is simply a process of chemical change, sometimes referred to as the “rapid oxidation of fuel.” Figure 21-1 shows a simplified illustration of the concept of oxidation.



What we’re illustrating here is a universally understood concept that in order to get fuel to burn, we need oxygen. To have a complete understanding of combustion, though, a technician needs to recall the third element that is necessary for this process to be accomplished. For example, in the form of a question….

Which combination is necessary to accomplish the combustion process?

A. Fuel, Hydrogen and Ignition
B. H20, Fuel and Ignition
C. Air, Fuel and Ignition
D. Nitrogen, Oxygen and Fuel

….to which the correct answer is “C”, we are offering up information on the third component necessary, which is heat. Heat, of course, can be in the form of a glow coil or spark igniter, or in a pilot flame. Of course, it’s the oxygen in the air (air is 20.91% oxygen, leaving 79.09% of it to be nitrogen and other chemicals) that actually allows for combustion to be accomplished, and while the only real answer to this question doesn’t have the term “oxygen” in its list, the commonly held understanding that oxygen is a part of air will lead you to the correct answer. (By the way….it’s also common to refer to the make-up of air as “about 21% oxygen and 79% nitrogen.) The reasoning behind the correct answer to this question is that the oxygen in the air is the only part of the air that is consumed.

Here are two other factors to consider regarding the idea of combustion actually being a process of chemical change:

The carbon in the fuel unites with the oxygen, forming carbon dioxide.

The hydrogen in the fuel unites with the oxygen, forming water vapor.

At least from the theory of perfect combustion that’s how it is. (See Figure 21-2)



In this illustration, we’re showing that the fuel (natural gas in this case) when combined with oxygen from the air (along with ignition) will result in a flame, which will result in carbon dioxide and water. This illustration also makes the case for being familiar with identifiers that are employed to explain the various chemicals in the combustion process.

An important point to remember from a nuts and bolts perspective about the combustion process is that we won’t be able to achieve that in the field, which means a technician needs to be familiar with carbon monoxide. Consider this question:

Carbon monoxide is identified by the symbol:

A. CO2
B. H2O
C. N2

“C”, of course, represents carbon (a component of the fuel) and “O” represents oxygen (a component of air). And, since carbon monoxide is a product of the interaction between fuel and air in the combustion process, the correct answer to our question is D. Carbon Dioxide (choice A), on the other hand, is identified by the symbol CO2. The point we want to make here about these two similar symbols is that being in a hurry or feeling “under the gun” during a test could result in an incorrect choice.

In our next segment, we’ll continue our discussion on CO, and how understanding a proper air-to-fuel ratio can minimize its production. Speaking of fuel…..

LP gas manifold pressure should be:

A. 3.5 in. W.C.
B. 14 to 16 in. W.C.
C. 10 to 11 in. W.C.
D. 6 to 7 in. W.C.

We’ll provide the answer to the next segment.




In this segment we’re going to get right to some questions regarding the evaluation of heat pump electrical circuits:



(Refer to the schematic in Figure 27-1) A customer calls to say that their residential heat pump is not cooling. You observe that the compressor and outdoor fan motor are not operating, and the indoor fan motor is. You determine that the thermostat is set properly.

A. The transformer could be the source of the problem.
B. The contactor has failed.
C. The control relay could be the source of the problem.
D. The thermostat has failed.

Like many certification exam questions, this one can be answered correctly through a couple of techniques. One of which is the process of elimination. Take “A” for example. It couldn’t be correct since the information in the question established that the indoor fan motor was operating. Ditto for the thermostat…..the question clearly states that the thermostat is properly set. (Yes, somebody’s interpretation of the term “proper” could be that the fan is set in the ON position rather than AUTO, thus allowing the fan motor to operate without the benefit of a call for cooling, but it’s doubtful that the author of the question would have that idea in mind….one simple rule for success in certification testing is not to try to read too much into a question.)

With the most obvious answers out of the way…even if we didn’t take a close look at the schematic, but instead relied on common application of experience and overall understanding of the operation of any comfort cooling system…we can focus on the two choices that are left. And we can easily arrive at the only answer that makes sense by accomplishing the tracing of the appropriate circuits on our diagram. Could “B” be the correct answer?

Well, let’s find out. Begin tracing at L1 and follow through the normally-open “C” contacts, then continue on through the run winding and start winding and run capacitor, then finish the trace by going through the other normally-open “C” contacts, and back to L2.

Accomplishing this trace proves that the outdoor fan motor isn’t in the contactor two-pole switch circuit at all. Only the compressor would be affected if the contactor had failed. We’re no longer relying on that overall understanding of a comfort cooling system we mentioned above. Since this is a heat pump, and we understand that the outdoor fan motor will have to be controlled (operating) in the heating and cooling modes, but turned off in a defrost mode, it must be controlled independently of the compressor.

To confirm this, begin again at L1, then go through the “CR” contacts shown wired in series with the OFM, again following on through both the motor windings and the run capacitor before completing the trace by going back to L2. What’s that? You’re wondering about that normally-closed set of contacts labeled “DFR” (Defrost Relay)? Well, don’t. It’s like they in New York City………… fuggetaboudit. This component, even though it has a set of contacts wired in series with the outdoor fan motor, were not mentioned in any of the choices, so it’s not a factor. The only thing that is a factor is another trace, this time on the control voltage segment of the diagram.

With the thermostat set to call for cooling, there is a circuit to both the CR coil and IFR coil. And energizing the CR coil is supposed to close two sets of contacts immediately…those in series with the contactor coil and those in series with the outdoor fan motor, the two components that were identified in our question as not operating. To nail this down, trace from the “R” wire connected to the transformer to the cooling switch and control shown on the “Y” wire that leads to the CR coil. From the parallel connection on the Y wire, follow on down to the G switch set to AUTO and on to the IFR coil. Both circuit traces can be completed from the other connection of both coils to the other side of the transformer.

Next question….

A customer residing in an extremely cold climate reports that their heat pump is not providing enough heat. You determine that the refrigeration system is accomplishing heat transfer according to its capacity. Electrical checks at SH1 and SH2 show a reading of 240 VAC. An amp check of SH2 shows no current draw.

A. The HC2 coil has failed.
B. The OTS2 outdoor thermostat has failed.
C. The SH2 element has failed.
D. The field-installed supplemental heat kit transformer has failed.

We’ll discuss the answer to this question in our next segment.

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