NATE A/C Certification Exam 2026/2027 –Verified Questions and Answers with Solutions | A+ Graded Practice Material

1 NATE A/C Certification Exam 2026/2027 –Verified Questions and Answers with Solutions | A+ Graded Practice Material NATE HVAC CERTIFICATION EXAM Exam 2026 / 2027 Academic Year Q: The duct systems within any HVAC system serve what purposes? Answer: They Carry warm air during the winter, Cool air during the summer and ventilate space to provide better air quality. Q: What types of Ducts are found in HVAC systems? Answer: Rigid and Flexibles Q: What are Rigid Ducts made of? Answer: Galvanized steel, polyurethane, and fiberglass 2 Q: Rigid Ducts are durable and are usually used for? Answer: Main trunk ductwork Q: How are flexible ducts designed? Answer: Have an insulated outer jacket surrounding a plastic film coil spring inner liner. Q: Where can flexible ducts be found? Answer: In the crawlspace, suspended from the floor joist Q: What are the benefits of flexible ducts? Answer: They fit easily into smaller spaces and around larger items. 3 Q: Adequate airflow is critical for the HVAC system. Why? Answer: To successfully operate Q: What are the Supply ducts? Answer: The ones that send conditioned air into each room Q: What are the return ducts? Answer: The one allows air to return to the air handler for distribution to the supply system. Q: What is the importance of adequate duct sizing? Answer: The system would not function efficiently 4 Q: During the cooling cycle the outdoor coil works as a? Answer: Condenser Q: During the hearing cycle the outdoor coil works as a? Answer: Evaporator Q: Indoor coils during the cooling cycle serves as a? Answer: Evaporator Q: The indoor coil of a heat pump works as an condenser during what cycle? Answer: Heating cycle? 5 Q: The compressor Answer: Is the heart of a vapor compression system used for cooling. Q: Refrigerants Answer: liquids that boil easily at low temperatures Q: Blower and fans Answer: Are the driving forces used to move air through ductwork Q: Air components Answer: Evaporator, condenser, compressor and metering device 6 Q: Evaporator coil Answer: It Boils refrigerant that absorbs heat from the air inside the space. Q: Condenser Answer: Reduces a vapor to a liquid by extracting heat Q: Compressor Serves as a pump, circulating refrigerant through tubing that connects indoor and outdoor Answer: components. Q: Metering devices Regulate how much liquid refrigerant enters the evaporator to achieve the desired refrigerant Answer: cooling conditions. 7 Q: Two types of registers Answer: Supply and returns Q: Q: Supply Registers are usually located on?? Answer: Outer walls or under windows Q: return registers Answer: Are usually installed up high on inside walls Q: What are registers equipped with? Answer: With air volume control devices, which allow them to mix air in the conditioned space 8 Q: Diffusers Answer: Are mechanical devices that slow the air and enhance its distribution within the space. Q: Where diffuser generally be placed in areas that need to be heated? Answer: On the floor Q: Where diffuser generally be placed in areas that need to be cooled? Answer: High in the wall so that the cooler air will move downward and increase natural circulation Electromechanical wall thermostats Answer: Are temperate sending devices that control HVAC systems and maintain comfortable temperatures inside a home or building. 9 Where thermostats not be installed? Answer: They must not be installed in a location where the air supply blows on them or in direct sunlight. Where are thermostats typically installed? Answer: Near return air grilles What components are commonly controlled by electromechanical thermostats? Compressors, condenser fan motors, evaporator fan motors, heaters and reversing valve solenoids. What's a electronic thermostat? An electronic thermostat is a microprocessor-based control that uses temperature-sensitive resistors called thermistors. According to what, does the resistance of a thermistor changes? According to the surrounding air temperatures What the circuitry of an electronic thermostat recognizes? 10 It recognized changes in resistance as changes in temperature. When the resistance decreases, what the current in the circuit does? The current in the circuit increases The higher the resistance means? lower current Supply air refers to? Air leaving the air handler Is supply air distributed throughout a section of ductwork called? Supply plenum Return-Air Typically passes through a filter before entering the air handler for the conditioning process, whether heating, cooling, or ventilating the space. What is a cross break? It is a creation of an angle on all sides of a rectangular section of metal duct-it will increase 11 rigidity and reduce vibration. turning vanes Rectangular elbow ductwork is used to reduce pressure loss and evenly distribute airflow. Dampers are used in duct systems to do what? To adjust airflow into each room Dampers Is a valve or plate that stops or regulates the flow of air inside a duct, chimney, air handler, or other air handling equipment. Supply blowers Deliver conditioned air to living spaces; ducts must be sized to match the statics pressure capability of the supply blower being used. Indoor Blower Deliver the necessary airflow through the heat exchanger and evaporator coils while developing an adequate amount of pressure. 12 Ducts must be properly sealed and ? Insulated what does the R-value in insulation means? Indicates how we'll it can resist heat flow What does induced draft mean? The combustion airflow is artificially created What are the three main components of a furnaces? Heat exchanger, Burners, induced draft blowers and added safety switch. heat exchanger Transfer heat from the combustion chamber to the supply air that is heating the conditioned space. Most heat exchangers are made of steel, often coated with another material to reduce corrosion. Burners The burner is where the heating element, usually has or oil, is held and burned. It's located in the middle of the furnace, just below the heat exchanger. 13 Blowers Induce draft blowers to force the combustion products through the heat exchanger and move them to the chimney or sidewall vents. Condensing Furnace A furnace that contains a secondary heat exchanger that extracts latent heat by condensing exhaust (flue) gases. Compass and a protractor user to measure angles, such elbows for duct works Measurement Depending on the project, you might be recording measurements such as inches, feet, centimeters, or millimeters sheet metal It is often used in the HVAC industry. As an HVAC support technician, you will be creating or fabricating, ducts and duct fitting for large and small HVAC systems. ceilings 14 Many HVAC components are located up high, near ceilings. Beams and Joists are two major ceiling components beams A main horizontal wood or steel Component of a building, runs parallel with the ceiling. It acts a central support. Joists These are small rectangular sections of wood that runs parallel from wall to wall in a building. Joist rest on beams and supports ceiling and floors walls At ceiling level ceiling joist rest directly on top of wall plates. Plates A piece of wood placed on wall surfaces that acts as a fastening device. Wall Studs Horizontal pieces such as beams and joists nailed to studs. 15 Bridging A brace made of wood or metal pieces which is place diagonally between the floor joists. Chase A groove that goes though the floor to accommodate pipes or duct. Chase are important when installing ductwork Girders The main component in a framed floor that supports the joists that hold the flooring board. Trusses Is a combination of structures creating a framework to connect load bearing walls. All holes cut through a joist It should be limited to the center of one-third of the joist. If the joist is cut incorrectly, the building's entire structure can be weakened. Post and Beams should never? Be cut without the approval of a qualified structural engineer. 16 All original walls should be considered what? Load bearing until they have been verified otherwise by a qualified structural analysis. Properties of matter are solid, liquid, gas Solid A form of matter that has a definite shape and volume This phase contain the least energy Liquids Definite volume, no definite shape, particles close together and medium amount energy. These molecules will fit the shape of any container Gases A state of matter has no fixed shape and takes on the shape of the space they're in. Contain the most energy of all of the phases. Thay are also know as vapors Mass 17 A measure of the amount of matter in an object Density Mass per unit volume of a substance is usually expressed as pounds per cubic footz Oxidation A chemical change in which a substance combines with oxygen, as when iron oxidizes, forming rust Combustion The combination of fuel and oxygen resulting on the release of heat. Three things must be present for combustion to happen. Fuel, Oxigen, and Heat Oxygen, fuel, and heat. These ingredients are often called the? Fire triangle Simple machines are? They are the smaller mechanisms or pieces that make up all larger machines. They can change 18 the direction or magnitude of a force Lever A strong bar used to lift and move heavy items wheel and axle A wheel with a rod, called an axle, through its center lifts or moves loads. Pulley Wheel or set of wheels of wheels using a rope or chain to raise and lower heavy objects inclined plane A slanting surface connecting a lower level to a higher level. Wedge Object with an inclined plane ending in a sharp edge, used for pushing objects apart Screw Inclined plane wrapped around a pole that can hold things together or lift things. 19 complex machine A complex machine is a machine made up of two or more simple machines working together. A blower or fan is a combination of a pulley machine( belt -driven fan or motor) a wheel and axle in the motor and the fan blades. conservation of energy The law of conservation of energy is a principle from physics. It states that energy is conserved over time. It is not created or destroyed Basic of fluid mechanics A substance that is in the liquid or gas phase is called a fluid. Fluid mechanics focuses on the properties of fluids. HVAC piping and ducting systems are designed based on principles of fluid mechanics Voltmeter A device used to measure voltage, or electrical potential energy difference Ohmmeter A device used to measure resistance and continuity in an electrical circuit. 20 Digital Multimeter Electronic test equipment that can perform multiple tasks. Typically one capable of measuring voltage, current, and resistance. More sophisticated modern digital multimeters also measure capacitance, inductance, current gain of transistors, and/or anything else that can be measured electronically. Voltage The force or pressure that pushes electrons through an electric circuit. It also know as electromotive force (EFM) or potential difference. What symbol represent voltage? E How Voltage can be created? Friction, Pressure, Heat, light, chemical reaction and magnetism. Amps (Amperes) An ampere or amp is an electron flow rate equal to one coulomb per second. Coulomb 21 Is a measurement of the quantity of electrical charge. Electrical current is measured in amps. Resistance Electrical resistance is the opposition to the flow of an electric current caused by certain physical characteristics of a conductor. symbol of resistance R Ohms symbol Omega Power Power is equal to the amount of work per unit time. Electrical power is measure in? Watts DC circuit A type of circuit that carries direct current, or current that flows in only one direction. 22 AC circuit A type of circuit that carries alternating current, or current that periodically reverses direction. A circuit a path for an electrical current to flow around A load A device that uses electrical energy to do work as generates heat. basic electrical circuit contains a power supply that is connected to a load via conductive wires Switches a device for making and breaking the connection in an electric circuit. closed switch Allows the current to flow by completing the circuit. 23 A voltage reading across a set of contacts indicates that The contacts are open A reading of 0 in a circuit 0 V May mean that the switch is closed Temperature A measure of how hot (or cold) something is; Humidity a measure of the amount of water vapor in the air Air Quality: HVAC It filters or clean the air materials that can accumulate on cooling coil and other mechanical components. Ventilation (HVAC) Ventilation in an HVAC system is the mechanical process of supplying or removing air to and from a space. An important function of the ventilation system is to bring fresh air from outside into the conditioned space. 24 Odor control Filters and electronics air cleaners work to purify the air inside the space, but they do not generally eliminate odor. Some odors can be eliminate with activated charcoal filters. Sound HVAC Keep equipments from costumers a far away as possible. It should be installed in basement, crawl space, utility room, attached garage or attic. Airflow source (noise High air velocity too much air might be moving past the damper or the damper might not be closed all the way. This is something you will check for when you troubleshoot a noise complaint. latent heat the heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without change of temperature. sensible heat the heat we can feel and measure with a thermometer 25 BTU The amount of energy needed to heat one pound of water one degree Fahrenheit BTU formula Weight x change in temperature Temperature A measure of how hot (or cold) something is; specifically, a measure of the average kinetic energy of the particles in an object. Temperature Conversions F = 9/5C + 32 K = C + 273 humidity a measure of the amount of water vapor in the air Relative Humidity (RH) The ratio of the moisture content of the air to the maximum possible moisture content at the same temperature. 26 Conduction It is where heat is transferred from a warmer substance to a cooler substance. The transmission of heat occurs whenever two objects of different temperatures are in direct contact with each other. Convection The transfer of thermal energy by the circulation or movement of a liquid or gas. The heat transfer occurs when at a faster rate than with conduction. Radiation Heat energy is moved through the environment. With radiation, the heat source and the thing that is being heated never touch, and nothings needs to love between the two. ( sunlight that is coming through a window) thermometer An instrument used to measure temperature Mechanical thermometers Are based on the fact that most substances expand when heated and contract when cooled. In the liquid-in-glass thermometer below, the liquid expands when heated and contracts when cooled to give a temperature reading. 27 electronic thermometers Measure temperate and display the results digitally. Manifold gauge set Used to measure HVAC/R pressures and saturated temperatures within a closed-system to evaluate or troubleshoot system's operation. Refrigerant line installation Need to be installed first before you can work on the ducts. What to do at the job site before installing Refrigeration lines? *Figure out the most practical way to run the lines. *Think about the types of bends *Determine the best starting point for routing lines inside and outside the structure. *make sure the tubing is long enough *uncoil the tubing, but do not link or dent it *Route the tubing, making all required bends, and properly secure it before making any connections. Bending copper tubing 28 It's important you do not affect the pipe diameters. This will create an unnecessary pressure drop that could reduce system capacity by decreasing the flow rate of the refrigerant. Brazing A form of welding used to heat the base metal temperatures above 700 degrees F but below it's melting points, prepares the tubing for installation. Brazing can join most ? Metals flux reduce what? Oxidation within the tubing When joining copper to copper, you would used what? Brazing alloy, because brazing alloy is stronger flare fitting Fitting that requires no soldering; designed to tightly fit against the tubing and mating parts. The flare fitting produce a seal that is resistant to pressure and won't leak. 29 Flare fitting installation *Inspect the tubing to make sure it is squarely cut and free of damage and debris, such a burrs or paint. *Slide the nut on the tube end with the threads facing outward. *Flare the end with the flaring tool. *Make sure end evenly flared and free of imperfections. *Thread the flare on to the fitting, and then secure it with two adjustable wrenches. Oxy acetylene welding equipment Are used for brazing because of their higher flame temperatures. Soft Soldering Soft soldering is a quick method of joining metals together. Hard Soldering Specific soldering that occurs at temperatures above 800 degrees Fahrenheit Installing metal Ductwork must be properly sealed and supported. Adequate support is necessary because if the duct sags, the sagging opens the joints. Proper joining methods are also critical for joints to remain leak free. 30 Installing Flexible Duct Flexible duct branches out from the main ductwork, taking conditioned air to different spaces within the home or building. It must be supported at regular intervals, not greater than 4 feat apart. Installing Ductboard What are four ways to fabricate a duct section from duct board? One piece duct, two-piece duct, two piece L duct and four piece duct. When fastening ductwork with screw what screw should you used? Screw that are at least half inch longer than board thickness. If securing ductboard to a metal use what screw? #10 sheet metal screws along with 2 and one half square washer What materials are approve for sealing duct board? pressure sensitive or heat activated aluminum foil tape, glass fabric tape, and mastic. 31 All sealing materials must conform to what? UL Standard 181 Use of aluminium foil tape over what? A stapled shiplap joint, . Staple the flap of the shiplap seam every two inches on center, then apply tape over the flap. The tape must be overlap the joint a minimum of one inch on both sides. Seal seams and joints without staple flaps tape cross tabs may be used imstead of staples. Criss tabs must be at least eight inches long, and should be placed perpendicularly across the taped joint at intervals of 12 inches. other guidelines to be observed when sealing ductboard include. • If ether the aluminum foil tape or the surface of the ductboard is below 50°F at the time of application, preheat the tape. • Pressure-sensitive aluminum foil tape must be at least 2 ½ in. wide. • Heat-activated aluminum foil tape must be at least 3 in. wide. •Heat-activated aluminum foil tape must be heated to a temperature of 550 to 600°F after being applied to the duct. The plenum will be installed where? On top of the evaporator coil or the air handler. 32 Where the plenum be secure? Near the ceiling with screws, plenum in air conditioning systems need to be insulated and include a vapor barrier. Flexible duct should not be used as plenum. Installing thermostat It should be installed approximately 5 feet above the floor on a interior wall. Do not mount thermostat; *where it will be exposed to direct sunlight *Near supply register or other sources of heat *Near outside doors or on an exterior wall *In or near the kitchen electronic air cleaners Use an electrostatic process to capture particles in the air. Where are electronic air cleaners installed? On the return air side 33 Installing humidifiers A bypass humidifier is connected between the supply side of the furnace and the return side. A fan powered humidifier is connected to the supply plenum. Wiring units and control wirings The most commonly used wire size for low voltage is?? 18AwG Supply circuit ampacity is used to ? Choose the appropriate wire size. Evacuation tools A deep evacuation procedure is necessary to remove air and contaminants from the system before use. Vacuum pump and micron gauge are vital for this procedure. Hvac Charging tools An electronic charging scale is an important device used to charge a system. It does with a specific amount of refrigerant often measured in ounces. 34 Recovery and Recycling machine Are need it to remove refrigerant from a system properly. These are used during the evacuation process. furnaces are usually installed *Basements *Crawl spaces *Attics *Closets *Garages heat transfer the movement of energy from a warmer object to a cooler object cooling cycle 1. The cold refrigerant absorbs heat from the hotter room in the evaporator, so the room will cool down. 2. It is then put through the compressor to increase its temperature. 3. It passes through the condenser coils, and transfers this heat to the outside air. 4. It then expands in order to decrease its pressure and cool down to below the room's temperature to repeat the cycle. 35 Split System An air conditioner that has the condenser and compressor outdoors and the evaporator indoors Packaged systems Easy to install and preassembled, this system may not last as long as a split system. heat pump system a two way heating system taking heat out of a home in summer and bringing heat in the winter planned maintenance Scheduled preventive maintenance tasks that occur on a regular basis. HVAC mechanical maintenance Dirty filters can cause high temperatures. Changing filters, cleaning dirty condenser fins, and evaporator fins are important. electrical maintenance Infared scans, clean and tighten connections, check that functioning within the right range (electrical multimeter, transformers should remain cool), labeling, updated plans, safety 36 equipment, lockout/tagout procedures, avoid water, energy management services Combustión planned maintenance Make sure firing rate of the burner is correct by verifying the manifold pressure matches manufacturer requirements. * when is available, check the gas meter for actual rate of gas usage as well. *In oil burners, check the oil pressure. * after stabilized operation test the products of combustion with a combustion efficiency analyzer and note the results. Then adjust setting the maximized efficiency. Low airflow over a residential split system air conditioning evaporator can cause A: Liquid flood-back to the compressor B: A decrease in compression ratio C: An increase in suction line superheat D: Oil logging in the evaporator A: Liquid flood-back to the compressor 37 Which of the following is the correct sequence of work? A: Attach gauge manifold, recover refrigerant, replace filter core, evacuate the system, recharge the system. B: Recover refrigerant, evacuate the system, replace filter core, recharge the system. C: Attach gauge manifold, evacuate the system, replace filter core, recover refrigerant, recharge the system. D: Attach gauge manifold, recharge the system, evacuate the system, replace filter core. A: Attach gauge manifold, recover refrigerant, replace filter core, evacuate the system, recharge the system. As the pressure on a liquid is increased, the vaporization temperature of the liquid A: Decreases B: Increases C: Remains unchanged D: Varies B: Increases 38 An oil separator must be mounted A: Level B: Below the compressor crankcase C: Above the compressor crankcase D: In the suction line A: Level Which of the following metering devices controls evaporator pressure? A: Thermostatic expansion valve B: Fixed orifice C: Low side float D: None of these D: None of these An automatic expansion valve controls evaporator pressure. 39 The purpose of the external equalizer on a thermostatic expansion valve is A: To equalize evaporator pressure drop with respect to the TEV B: To equalize the evaporator pressure drop C: To help prevent liquid floodback D: To allow the high side pressure to equalize to the low side when the compressor cycles off A: To equalize evaporator pressure drop with respect to the TEV The higher the MERV rating of a filter-drier, the A: More efficient the drier at absorbing moisture B: Less efficient the drier at absorbing moisture C: Smaller the particles the filter can entrap D: MERV does not apply to filter-driers D: MERV does not apply to filter-driers Minimum Efficiency Reporting Value - MERV ratings are used to rate the ability of an air 40 conditioning filter to remove dust from the air as it passes through the filter. MERV is a standard used to measure the overall efficiency of a filter. Higher MERV ratings mean fewer dust particles and other airborne contaminants pass through the filter. Filters with a merv rating of 9 to 12 are used in commercial and industrial applications and will stop particles in the 1 to 3 micron range. These filters are a great choice for home owners who want the best dust control possible. When using filters with Merv 9 ratings and above it is important to clean or replace them when recommended by the manufacturer because they will have a negative effect on air flow when they become dirty. This can lead to performance problems and decreased operating efficiency. The most efficient filters have merv ratings of 13 to 16 and will stop particles as small as .3 microns. These filters are used in hospitals and other super clean environments. Zeolite is used with A: Refrigerant filter-driers B: HEPA filters C: Pipe threads D: Solder A: Refrigerant filter-driers Vacuum pressures are measured in 41 A: Microns B: Millimeters of mercury C: Inches of mercury D: All of the above D: All of the above The number 25,400 relates to A: Microns/inch B: Btu/ton C: Cfm/hp D: Cfm/ton A: Microns/inch The general rule of thumb for airflow is A: 400 cfm/ton 42 B: 400 cfm/hp C: 6 cfm/sq D: 144 cfm/cu A: 400 cfm/ton A double suction riser is used to A: Help improve refrigerant return B: Allow the compressor to pump at a greater capacity C: Decrease suction line resistance D: Improve oil return as system capacity changes D: Improve oil return as system capacity changes A service technician measures a return air temperature of 80 degrees and a supply air temperature of 55 degrees. What, if anything, may be wrong with this air residential split system air conditioning unit? A: Low on refrigerant charge 43 B: Low on evaporator airflow C: Refrigerant overcharge D: There is probably nothing wrong with the system B: Low on evaporator airflow The normal compression ratio for a typical comfort air conditioning application should be in the range of A: 1 to 2 B: 1.5 to 2.25 C: 2 to 3 D: 2.75 to 3.75 D: 2.75 to 3.75 Compression rate = discharge pressure (psia) / suction pressure (psia) All else being normal, if a system shows a high lowside superheat with high condenser subcooling, what is most likely the problem? 44 A: Refrigerant overcharge B: Refrigerant undercharge C: A partial refrigerant restriction D: There is probably no problem C: A partial refrigerant restriction All else being normal, if a system shows a low lowside superheat with high condenser subcooling, what is most likely the problem? A: Refrigerant overcharge B: Refrigerant undercharge C: A partial restriction D: There is probably no problem A: Refrigerant overcharge All else being normal, if a system shows a high lowside superheat with low condenser subcooling, what is most likely the problem? 45 A: Refrigerant overcharge B: Refrigerant undercharge C: A partial restriction D: There is probably no problem B: Refrigerant undercharge A grille equipped with a damper control is called A: A vane B: A register C: A louver D: A damper B: A register A pressure relief valve is A: Direct pressure acting 46 B: Remote pressure activated C: Manually operated D: Reverse pressure acting A: Direct pressure acting A parallel compressor system in which both the crankcase oil level and the refrigerant gas pressure are equalized is a A: Double pipe crankcase equalizer system B: Single pipe crankcase equalizer system C: External equalizer oil system D: Crankcase hot gas oil equalizer A: Double pipe crankcase equalizer system In a direct expansion chiller used on air conditioning applications, the refrigerant is on what side of the tubes? A: Around the diverter 47 B: In the tubes C: Surrounding the tubes D: On both sides B: In the tubes The total minimum open area for air to flow through on a supply air register is called A: Free area B: Open area C: Core area D: Drop area A: Free area Which type of copper tubing has the thickest wall? A: Type L B: Type K 48 C: Type M D: Type DWV B: Type K Types K, L, M, DWV and Medical Gas tube are designated by ASTM standard sizes, with the actual outside diameter always 1/8-inch larger than the standard size designation. Each type represents a series of sizes with different wall thicknesses. Type K tube has thicker walls than Type L tube, and Type L walls are thicker than Type M, for any given diameter. All inside diameters depend on tube size and wall thickness. Copper tube for air-conditioning and refrigeration field service (ACR) is designated by actual outside diameter. What is the gross weight of a refrigerant cylinder? A: The weight of the cylinder minus the refrigerant B: The weight of the cylinder plus the weight of the refrigerant C: The weight of cylinder's refrigerant capacity D: The weight of the cylinder and the box around the cylinder B: The weight of the cylinder plus the weight of the refrigerant 49 What does an anemometer measure? A: Feet B: Feet per minute C: Cubic feet per minute D: Vacuum pressure in microns A: Feet The anemometer only measures feet while the operator uses a stop watch or second hand on a watch. This is a typical "trick" question to watch for The term "induced draft" most likely refers to A: A compressor B: A type of control C: A type of cooling tower D: A type of test instrument C: A type of cooling tower 50 What fitting should be used to connect 1⁄4" copper tubing to a 1⁄4" internal pipe thread opening on a compressor crankcase? A: A union B: A half union C: A tee D: A street ell B: A half union Which of the following compressors has the fewest moving parts? A: Rotating vane rotary B: Fixed vane rotary C: Scroll D: Reciprocating C: Scroll 51 A hot liquid line with a low to normal high side pressure is an indication of A: An overcharged system B: An undercharged system C: Air in the system D: A restricted filterdrier B: An undercharged system Air and water are directed counterflow so as to A: Average the flow rate B: Gain the greatest amount of heat transfer C: Reach the lowest apparatus dew point D: Control the humidity B: Gain the greatest amount of heat transfer Which of the following applications is not a mechanical cooling system? 52 A: Cascade system B: Reciprocating compression system C: Evaporative cooling D: Centrifugal compression system C: Evaporative cooling A compressor is short cycling. Which of the following would not be the cause? A: Low pressure controller differential set too close B: Automatic reset high pressure control differential set too close C: Low refrigerant charge D: Leaking compressor suction valve D: Leaking compressor suction valve The position of the valve stem on the suction service valve is normally A: Fully-back-seated 53 B: Full-front-seated C: Mid-seated D: Half cocked A: Fully-back-seated Of the three fundamental fan laws, one states that the power varies by the ______ of the speed. A: square B: cube C: rate D: inverse B: cube BHP2 = BHP1 x ((CFM2/CFM1)cubed) Abnormally low suction pressure can be caused by which of the following? A: Dirty air filter 54 B: Partially restricted filter-drier C: Shortage of refrigerant D: Any or all of these D: Any or all of these Which of the following compressor oil types is generally considered the most compatible with HFC refrigerants? A: POE B: AB C: Mineral D: Vegetable A: POE The factor determining the correct quantity of air for each room in a building is A: The calculated heat load for each room 55 B: The size of the room C: The size of the ducts D: The customer's preference A: The calculated heat load for each room Refrigerant 22 is classified as an A: A1 refrigerant B: A2 refrigerant C: B1 refrigerant D: B2 refrigerant A: A1 refrigerant ANSI/ASHRAE 34 published in 2001 and entitled "Designation and Safety Classification of Refrigerants". • Class A signifies refrigerants for which toxicity has not been identified at concentrations less than or equal to 400 ppm; • Class B signifies refrigerants for which there is evidence of toxicity at concentrations below 400 ppm. • Class 1 indicates refrigerants that do not show flame propagation when tested in air at 21°C 56 and 101 kPa; • Class 2 indicates refrigerants having a lower flammability limit of more than 0.10 kg/m3 at 21°C and 101 kPa and a heat of combustion of less than 19 kJ/kg; • Class 3 indicates refrigerants that are highly flammable as defined by a lower flammability limit of less than or equal to 0.10 kg/m3 at 21°C and 101 kPa or a heat of combustion greater than or equal to 19 kJ/kg. Which of the following combinations of instruments can be used to measure airflow in cfm on an electric furnace? A: A thermometer, ammeter and voltmeter B: A thermometer, tachometer and voltmeter C: A tachometer, pitot tube and ammeter D: A gauge manifold set, thermometer and voltmeter A: A thermometer, ammeter and voltmeter 1. Take the temperature difference (TD) across the furnace. 2. Measure the amp draw of the electric heaters only, and the applied voltage. 3. Determine the Kw output of the electric heaters (Kw = (A x V) / 1000 4. Determine the total output in btuh (btuh = Kw x 3415 5. Determine the cfm of the furnace with the formula: (cfm = btuh / (1.08 x TD) Example: TD = 25deg F; (Kw = 22a x 230v = 5060 / 1000 = 5.06Kw); (btuh = 5.06 x 3415 = 57 17,279.9); (cfm = (17,279.9) / (1.08 x 12) = 17,279.9 / 12.96 = 1333.3 cfm A rotating vane anemometer measures A: CFM B: RPM C: FPM D: Feet D: FPM A lockout relay is also called A: An impedance relay B: Reset relay C: Neither a or b D: Both a and b D: Both a and b 58 A lockout relay can be reset by A: De-energizing the main power B: Pushing the reset button C: Turning the breaker off and back on D: All of the above D: All of the above A voltage measured across a switch means A: The switch is closed B: The switch is open C: The switch is bad D: The switch is wearing out B: The switch is open When installing add-on split system air conditioning for a residence, you should never 59 A: Drill holes through outside cement walls B: Fish new thermostat wires through walls where power wires are also located C: Fish thermostat wires inside EMT along with power wiring D: Install the new evaporator coil in a down-flow style furnace cabinet C: Fish thermostat wires inside EMT along with power wiring In a series circuit, the current A: Is the same throughout the series path B: Varies according to the wire size C: Is always one half the voltage D: Passes the voltage on its way back A: Is the same throughout the series path Jumping a wire across terminals R and G on the sub-base of a thermostat will cause A: The blower motor to operate 60 B: The condenser fan to come on C: The gas valve to become energized D: The compressor to start A: The blower motor to operate A fully hermetic compressor on a 3 ton residential split system has three electrical terminals on the side of the compressor. An ohmmeter reads the following: terminal A to B = 20 ohms, A to C = 15 ohms and B to C = 5 ohms. There was a reading of infinity between all three terminals to ground. Which terminal is the common terminal? A: Terminal A is common B: Terminal B is common C: Terminal C is common D: There is no common terminal on this type compressor C: Terminal C is common To determine the common terminal, find the to terminals with the highest reading. The terminal left over is the common terminal. Put the probe on the common terminal and either of the other two terminals, highest reading is the Start terminal, and the other is the run terminal. 61 A 3ton residential split system should move about how many CFM total? A: 800 CFM B: 1000 CFM C: 1200 CFM D: 1500 CFM C: 1200 CFM Rule of thumb, tonnage x 400 = cfm; 3 x 400 = 1,200cfm An R22 air conditioning system is operating with a head pressure of 220 psig and a suction pressure of 68.5 psig. A temperature measurement taken on the suction line 8 inches from the suction service valve reads 60 degrees. A temperature measurement taken on the liquid line leaving the condenser reads 90 degrees F. What is the low side superheat? A: 10 degrees of superheat B: 15 degrees of superheat C: 20 degrees of superheat 62 D: 30 degrees of superheat C: 20 degrees of superheat Convert suction pressure to temperature using a P.T. chart. Subtract the saturation temperature from the suction line temperature. (60 - 40 = 20 deg F superheat) A hot wood stove gives up heat to the room by A: Conduction B: Convection C: Radiation D: All three at the same time D: All three at the same time