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hvac exam
| Question | Answer |
|---|---|
| Two location where a cold air return should be installed: | Open area of wall and low to the ground |
| Law of thermodynamics: | Heat moves toward a place with lower intensity |
| Sensible heat describes ___________________. | How hot something feels |
| Latent heat measures ___________________. | The heat potential of a substance. |
| Latent heat is measured in ________________. | British Thermal Units (BTU) |
| If 1 pound of water warms to 60 degrees F from 55 degrees F, what BTU of latent heat will it have absorbed? | 5 |
| What is the amount of heat energy required to evaporate 1 pound of water? | 970 BTU |
| In an air conditioning and refrigeration system, what occurs in an evaporator? | The refrigerant absorbs the latent heat. |
| In an air conditioning and refrigeration system, what occurs in an condenser? | The refrigerant releases the latent heat. |
| In a sealed system, pressure and temperature __________________. | Follow each other up and down |
| List type of compressor? | Reciprocating rotary screw centrifugal |
| In Fahrenheit, the boiling of water is ________________/ | 212 degrees |
| To change Fahrenheit to Celsius, what formula is used? | C = ( F-32) / 1.8 |
| method by which heat may be tranferred from a warmer substance to a colder substance? | Retraction |
| What BTU of heat is required to raise 1 pound of ice 1 degree F when the temperature is below 32 degrees F? | .5 |
| A day-ton of refrigeration is the amount of refrigeration produced by melting 1 ton of ice at a temperature of 32 degrees F in 24 hours. (true or false) | true |
| Ice exerts pressure __________________. | Downwards |
| Pressure is usually measured in ______________. | Pounds per square inch |
| Atmospheric pressure, at sea level, is _________ psia | 14.7 psia |
| When one rises into the atmosphere, the atmospheric pressure decreases by 1 psi for every _________________. | 2,343 feet |
| Vaporization can be increased by __________________ the pressure on a liquid. | Reducing |
| Every mechanical refrigeration system has ___________ different pressure levels. | 2 |
| Pressure on the high pressure side of a mechanical refrigeration unit is called _______________. | Discharge or head pressure |
| The exertion of pressure on a substance with a constant temperature increases its volume in proportion to the increase in pressure. | false |
| What is the symbol for impedance? | Z |
| The safety ground conductor for A/C circuit is usually color coded ___________. | Green |
| Heat which causes a change in temperature of a substance is called: | Sensible heat Any time there is a change of temperature indicated by the thermometer the heat level or intensity can easily be measured. In the writing of the early scientists who provided the foundations of thermodynamics, sensible heat had a clear me |
| What is heat, which causes a change in the state of a material without a change in temperature, called? | Latent heat Heat, which causes a change of state without a change in temperature, is known as latent heat. An example of latent heat is water changing to ice or vice a versa. Latent heat is the heat released or absorbed by a body or a thermodynamic sys |
| What is a sling psychrometer used to measure? | Wet and dry bulb temperature A sling psychrometer is a device that consist of two thermometers fitted in a hinged bracket used for spinning the two thermometers. One of the bulbs is kept moist with distilled water on a sock or wick placed over the thermo |
| A compressor is operating with a discharge pressure of 235.3 psig and a suction pressure of 35.3 psig. What is the compression ratio (pumping ratio) | 5:1 Compression ratio is found by dividing the absolute discharge pressure by the absolute suction pressure. PSIG is converted to absolute by adding 14.7 to the pressure. In this problem, discharge pressure 235.3 plus 14.7 equals 250 PSIA and the suct |
| In a (direct expansion) evaporator, liquid refrigerant must boil away as close to the end of the coil as possible in order to: | Operate at high efficiency Direct type evaporators are designed to operate most efficiently with approximately 10 degrees superheat. In order to have superheat, all liquid must be boiled away before reaching the end of the evaporator |
| An thermal expansion valve that is stuck wide open will cause ___________. | A flooded evaporator A valve that is in the maximum open position will have liquid refrigerant flowing at a rate faster than the evaporator could boil it away; thus creating a flooded coil and liquid refrigerant going back to the compressor |
| What is the major difference between a heat pump and an air conditioner? | Reversing valve The reversing valve is the component that will reverse the flow of refrigerant when changing from air conditioning to heating |
| What device controls the supplementary electric heat according to the outdoor temperature? | Outdoor ambient thermostat To control energy, the heat pump will incorporate outdoor thermostats to limit the auxiliary heat before the balance point is reached |
| Which of the following is not a factor that should be considered when installing an outdoor unit? | Return air When installing the outdoor unit the return air is not a factor in the installation; all of the other answers are factors involving installation |
| What is the minimum clearance for access panels on an outdoor condensing unit? | 30 inches When installing the outdoor unit the return air is not a factor in the installation; all of the other answers are factors involving installation |
| One BTU is the amount of heat required to raise the temperature of: | One pound of water one-degree Fahrenheit. One BTU is the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit. The pound of water absorbs 1 BTU of energy to change from 68°F to 69°F. |
| What is the primary compposition of natural gas? | 95 percent methane Natural gas distributed for consumer use is 95.4 % Methane, 2.2 % Ethane, 1.6 % Nitrogen, 0.5 % Carbon Dioxide, 0.2 % Propane, .04% butane, .01% Oxygen and .05 % miscellaneous gases. |
| The electric heat element is usually made of what material? | Nickel and chromium Heat elements are made of Ni-chrome which is nickel and chromium. They are combined to create a resistance wire |
| Which of the following is an example of a resistive load? a. Bimetal switch b. Crankcase heater c. Transformer d. Motor | Crankcase heater A resistive load is an electrical load in which voltage and current are in phase and are converted to energy in the form of heat. Other examples of a resistive load are electrical heaters and incandescent bulbs. |
| An oversized heating and cooling system can cause which of the following? a. Operating cost and relative humidity in the structure will decrease significantly. b. Moisture damage to a furnace heat exchanger and inadequate humidity removal during | Moisture damage to a furnace heat exchanger and inadequate humidity removal during cooling cycles. Over sizing a system will cause short cycling which will cause moisture problems. In the summer, not enough moisture will be removed making the structure |
| When the temperatures of a structure both inside and outside are equal, there is _____. a. no heat transfer b. latent heat transfer to the outside c. thermal heat transfer of sensible heat d. a lower rate of relative humidity | No heat transfer In order for heat to transfer there must be a difference in temperature. This follows the second law of thermodynamics. (Heat travels from a warmer area to cooler area.) |
| Polyolester (POE) oils stored in plastic containers will _______. a. separate b. become more alkaline c. become acidic d. absorb moisture through the plastic | Absorb moisture through the plastic Polyolester (POE) Oils are very hygroscopic and must be stored in a metal containers. Plastics containers may be permeable to moisture. |
| R-407C has _______-. a. a foul odor b. to be charged in the vapor phase c. the ability to fractionate d. no temperature glide | The ability to fractionate R-407C is a near-azeotropic ternary blend of hydrofluorocarbons refrigerants. It contains difluoromethane (R-32), pentafluoroethane (R-125) and 1,1,1,2-tetrafluoroethane (R-134a) which all have different pressure temperature |
| What is a carbon footprint? a. The carbon deposits from burning gasoline. b. The amount of carbon dioxide that is produced to support your lifestyle. c. The amount of carbon in the atmosphere produced by the world's lifestyle. d. The amount of | The amount of carbon dioxide that is produced to support your lifestyle. A carbon footprint is an estimate of how much carbon dioxide is produced to support a person's lifestyle. Essentially, it measures an individual's impact on the climate based on h |
| What is energy management? a. A rule that the total amount of energy stays constant in an isolated system over time. b. Recovering energy lost while using mechanical equipment. c. Reading the electric and fuel gas meters every month. d. The mo | The monitoring and controlling of energy consuming devices. Energy management is a very broad term used to cover the entire field of energy and its use. Energy management can be subdivided into more specific areas such as purchase utility, energy consu |
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