C20 Practice Test
What makes the best insulator? A. lightweight material with many air pockets B. lightweight material with no air pockets C. heavy material with many air pockets D. heavy material with no air pockets
A. lightweight material with many air pockets
When may a Type-B gas venting system be used? A. on gas venting systems serving appliances equipped with draft hoods B, on gas venting systems serving gas-fired vented wall furnaces C. on any gas venting system D. never
A. on gas venting systems serving appliances equipped with draft hoods
How do you determine the minimum size duct needed for a furnace? A. rated output in Btu/h B. power of fan in HP C. size of room in sq ft D. the size of supply air ducts are based on the size of return air ducts
A. rated output in Btu/h
A junction box used for joining wires may be made of: A. porcelain B. metal C. plastic D. all of the above
D. all of the above
What happens when the current in an electric circuit is reduced?
Heating effect decreases
When hooking up two fans in parallel, where should the thermostatic bulb be placed?
On the outlet of the evaporator/ suction line
What is the maximum spacing of support straps for horizontal ductwork?
10 ft
When adjusting gas-fire furnaces for elevations above 2,000 feet, the Btu/h input should be reduced 4% for each _____ above sea level.
1000 ft
What is the maximum spacing of support straps for vertical ductwork?
12 ft
What is the maximum temperature of hot air to blow out from a furnace?
250 F
How many sides does an ogee offset have?
4
The optimum air-fuel ratio for natural gas in gas burners under standard conditions is approximately ________ to 1.
9.5
The CAL/OSHA exposure limit for asbestos is: A. 0.1 f/cc B. 0.3 f/cc C. 1.0 f/cc D. 3.0 f/cc
A. 0.1f/cc
What is the overfire rating on a small draft hood? A. .02'' wg B. .04" wg C. .06" wg D. .08" wg
A. 02"wg
What is the minimum clearance between an air duct and a rafter? A. 1" B. 2" C. 3" D. 4"
A. 1"
What is the minimum size air-supply duct that must be installed for a 60,000 Btu/h blower-type furnace? A. 12" x 10" B. 30" x 10" C. 12" x 20" D. 20" x 40"
A. 12" X 10"
What is the minimum gauge sheet metal that can be used for ducts conveying Class 4 contaminants? A. 16 ga B. 18 ga C. 20 ga D. 22 ga
A. 16 ga
Where should you install the thermostat in a two-story house? A. 1st story near the air return B. 2nd story on an interior wall C. 2nd story on an exterior wall D. 1st story on an exterior wall
A. 1st story near the air return
Which wire can carry the most current? A. 4 AWG B. 6 AWG C. 8 AWG D. 10 AWG
A. 4 AWG
What is the best way to maintain a drive belt motor setup? A. according to manufacturer's manual B. according to experience with own drive belt motor C. replace bearings every 6 months D. replace bearings every 12 months
A. According to manufacturer's manual
If the side rail of a ladder is split away from the rungs, what should you do with the ladder? A. Discard B. Tie railing together with wire C. Use special reinforcement to attach D. Cut in half to make two smaller ladders
A. Discard
Which of the following solders has a melting point below 1150°F? A. Easy-Flo 45 B. Unibraze 50 C. Sil-Flos D. Unibraze 0
A. Easy Flo 45
How do you add moisture to a space? A. humidifier B. dehumidifier C. duct damper D. hydro couple
A. Humidifer
Which of the following affects temperature in a room? A. radiation B. dehydration C. irradiation D. deradiation
A. Radiation
Which gage would you use to test manifold gas pressure? A. U-tube water manometer B. 0-150 psi pressure gage C. a thermocouple gage D. any Bourdon-type gage
A. U-tube water manometer
You have a multiple zone A/C system, and 3 rooms are temperature satisfied. One of these rooms is cooler than the other two. Which of the following dampers is open? A. all 3 rooms B. the room which is cooler C. The return register D. none of the above
A. all 3 rooms
How long should duct runs be? A. as short as possible B. as long as possible C. whatever is convenient D. either very long or very short
A. as short as possible
A C-20 HVAC contractor is allowed to: A. connect aluminum wire to copper wire using a wirenut B. re-use refrigerant that is removed from the system C. use compressed oxygen to clean condenser cone D. use a blow torch without a fire extinguisher nearby
A. connect aluminum wire to copper wire using a wirenut
What are used to change air direction in ducts? A. elbows B. dampers C. baffles D. any of the above
A. elbows
A cable contains a black wire, a white wire, and a smaller, uncoated copper wire. What should you do with the uncoated copper wire? A. ground it B. splice it C. cut it off D. insulate it
A. ground it
Using an oversized fuse will affect the circuit by: A. reducing protection B. increasing protection C. less current will flow in the circuit D. No effect
A. reducing protection
Where is a scroll compressor normally used? A. residential and light commercial air conditioning B. commercial and industrial air conditioning C. supermarket freezers D. ice boxes
A. residential and light commercial air conditioning
Double-pane windows work best in climates where: A. the outside temperature is very hot and/or very cold B. the outside temperature is relatively constant C. there is a high exposure to direct sunlight D. there is a high level of humidity
A. the outside temperature is very hot and/or very cold
The needle on a volt-ohm meter needle shows infinite ohms on the high ohm scale. What does this indicate? A. the switch or circuit is open B. the switch or circuit is overloaded C. the switch or circuit is closed D. the switch or circuit is underloaded
A. the switch or circuit is open
Where do you find the ideal tension for a belt and pulley? A. the tension is given by the manufacturer B. base it on your own experience C. local building codes D. Cal/OSHA
A. the tension is given by the manufacturer
What happens when the motor on an air conditioning unit overloads? A. the unit shuts down B. the unit catches fire C. the unit runs on overload D. An alarm bell goes off
A. the unit shuts down
The type of bulb that measures evaporative cooling is called: A. wet bulb B. psychometric bulb C. thermostatic bulb D. dry bulb
A. wet bulb
Which of the following refrigerants are the most deadly? CFCs HCFCs HFCs all are equally hazardous
All are equally hazardous
A hermetic compressor is running and stable. What is the maximum amount of oil that should be in the sight glass? A. none B. 1/2 full C. 2/3 full D. 3/4 full
B. 1/2 full
Silver solder starts to flow at or above approximately what temperature? A. 1000°F B. 1150°F C. 1350°F D. 1400°F
B. 1150 F
You are working on a residential A/C system that uses a charge of more than 50 pounds of freon. What is the maximum annual leakage rate permissible before you must repair the leaks when you are servicing the system? A. 10% B. 15% C. 20% D. 50%
B. 15%
How high must a 12" diameter flue pipe project above a pitched roof line? A. 1 ft B. 2 ft C. 3 ft D. 4 ft
B. 2 ft
A room has a 1,200 sq ft ceiling. The specs require 1 sq ft of register per 150 sq ft of ceiling. What is the smallest register you may use? A. 2' x 2' B. 2' x 4' C. 3' x 3' D. 3' x 5'
B. 2' x 4'
What is the minimum safe landing clearance diameter for a helicopter? A. 100 feet B. 200 feet C. 500 feet D. 1000 feet
B. 200ft
If a furnace is installed in the attic, the minimum access opening is: A. 24" x 24" B. 22" x 30" C. 30" x 36" D. 36" x 36"
B. 22" X 30"
Which is true of a house entrance that supplies an outlet with two hot wires? A. 3-phase B. 240 V C. 300V D. 24V
B. 240V
If you installed a heating system and some rooms are much colder than the rest of the house, you should: A. try to separate the house into zones and add more thermostats B. adjust the damper in every room C. extend the plenum D. replace the fan
B. Adjust the damper in every room
What would you use to remove a screw or a bolt that has worn out due to fatigue and rust? A. Jaw grip wrench B. Cold chisel C. Apply more force to the wrench D. use two wrenches, holding one stationary, while using the other to twist
B. Cold chisel
What type of gage would you use for very high vacuums? A. thermistor B. McLeod C. Bourdon D. Pascal
B. McLeod
Calculate the heat loss through a 12' x 12' ceiling over a period of one hour for the following conditions: indoor design temperature = 75°, outdoor temperature = 50°, heat coefficient = 1.13 A. 3,750 Btu B. 4,068 Btu C. 6,291 Btu D. 79,230 calories
B. Q = U x A x TD x 1 hr. 1.13 x 144 x 25 x 1 = 4,068
Duct systems should be constructed according to: A. ASTM Standards B. Uniform Mechanical Code C. SMACNA Standards D. Cost
B. Uniform Mechanical Code
Which of the following best describes carbon monoxide? A. a colorless, odorless gas which is never deadly B. a colorless, odorless gas which can be deadly C. a gas which is used to displace oxygen D. a gas which is similar to CFCs
B. a colorless, odorless gas which can be deadly
Where in a furnace venting system may a Type-BW gas vent change to Type-B gas vent? A. whenever the wall space is large enough to allow the Type-B vent B. after the Type-BW vent passes through the highest ceiling plate above the furnace that it serves C. after the Type-BW vent passes through the lowest ceiling plate above the furnace that it serves D. never
B. after the Type-BW vent passes through the highest ceiling plate above the furnace that it serves
For most refrigerants, the boiling point at atmospheric pressure is: A. above 0°F B. below 0°F C. exactly 0°F D. either A or C
B. below 0 F
What is indicated when you hook up a continuity tester to a circuit and the test light goes on? A. open circuit B. completed circuit C. circuit is grounded D. circuit is not grounded
B. completed circuit
What would you use to solder ducts on a roof? A. soldering gun B. propane gas torch C. cutting torch D. any of the above
B. propane gas touch
What does a pumpdown cycle do? A. removes excess water B. removes refrigerant from the low pressure side C. removes oil from the refrigerant lines D. slows the motor
B. removes refrigerant from the low pressure side
In a central A/C unit that uses a large volume fan, how can you reduce the noise? A. use a silencer B. use sound dampening material to make a resilient mounting base C. use a rigid direct drive coupling D. place adjacent to the most important living areas
B. use sound dampening material to make resilient mounting base
Ducts conveying flammable dusts must have a clearance from combustible materials of not less than: A. 25" B. 24" C. 18" D. 15"
C. 18"
What is the minimum gauge for an aluminum duct that can be used to convey contaminants? A. 18ga B. 20ga C. 22ga D. 24ga
C. 22ga
What is the maximum allowed distance between support straps for flexible duct? A. 2' B. 4' C. 6' D. 8'
C. 6'
How are fuses rated? A. ohms B. watts C. amps D. kilowatts
C. Amps
A difference between a gravity-type heating system and a forced-air system is that the gravity-type relies on the _____ for air distribution.
C. Difference between hot and cold air
What is a DDC? A. Direct Draft control B. Direct drive connection C. Direct digital control D. Digital discharge coupling
C. Direct digital control
What is the maximum length flexible connector you can use for a heating furnace? A. 1' B. 2' C. 3' D. No maximum
C. Flexible connectors for fuel gas are limited to 6 feet for indoor appliances or 15 feet for outdoor appliances. Flexible metallic connectors connecting the water heater to water piping are limited to 2 feet in length. Since 2 feet is not offered as an answer choice, you must presume the question is asking about the fuel connector.
What should you reverse if you want to reverse the motor turn direction on a 460V 3-phase motor? A. L1 and T4 B. L2 and T4 C. L1 and L2 D. you can't reverse the motor turn direction
C. L1 and L2
What type of flame is desirable when you solder? A. carburizing B. oxidizing C. neutral D. none of the above
C. Neutral
Calculate the heat loss through a 6' x 6' window over a period of 24 hours for the following conditions: inside temperature = 68°F, outside temperature = 62°F, U-value = 1.13 4,216 Btu 4,764 Btu 5,858 Btu 25,829 calories
C. Q = U x A x TD x 24 hr. 1.13 x 36 x 6 x 24 = 5,857.92 Btu.
Which of the following is allowed in gas piping? A. copper pilot tube B. PVC gas piping C. brass fitting D. copper piping
C. brass fitting
When designing a heating system, with which of the following should you be most concerned? A. coldest outside temperature on record B. coldest inside temperature on record C. coldest outside temperature expected in a normal season D. coldest inside temperature expected in a regular season
C. coldest outside temperature expected in a normal season
What is the first thing you should do before removing a contactor? A. replace the coil B. clean the terminals C. disconnect the power supply D. adjust the pressure connector
C. disconnect the power supply
Which of the following condensers is the most efficient? A. air-cooled B. water-cooled C. evaporative D. all of the above are equally efficient
C. evaporative
When working around electrical equipment, what type of ladder should you use? A. steel B. Aluminum C. fiberglass D. any of the above
C. fiberglass
The Total Heat Loss Formula is used to estimate fuel cost, but it fails to account for: A. total hours of heating during the year B. BTU/unit of heat C. heat gain from solar, appliances or body heat D. outside/inside temperature difference
C. heat gain from solar, appliances or body heat
Where should you locate registers for a forced warm-air system? A. along an outside wall B. along an inside wall C. high on a wall D. on the floor or low on a wall
C. high on a wall
The size of gas piping is determined by the: A. number of burners and altitude above sea level B. volume of heat loss of area C. quantities of gas and pressure applied to unit D. number of burners and orifice size
C. quantities of gas and pressure applied to unit
Which of the following is the most common method of joining flexible ducts? A. flanges B. adhesive C. tape D. screws
C. tape
When you have a powered exhaust from a building, the make-up of the air vent will be: A. smaller than the exhaust air vent B. larger than the exhaust air vent C. the same size as the exhaust air vent D. unrelated to the exhaust air vent
C. the same size as the exhaust air vent
To adjust the fan limit in summer in a building with no A/C system, you should: A. turn the adjustment up B. turn the adjustment down C. turn the fan switch from "auto" to "on" D. turn the fan switch from "on" to "auto"
C. turn the fan switch from "auto" to "on"
Listening carefully to what a customer is telling you _____________________.
Can help you diagnose the problem
The volume of a poorly insulated room is 20,900 cu ft. A desired temperature change per hour requires 5.5 Btu/h per cu ft to achieve. What size heat pump compressor is needed to heat the space? A. 40,000 Btu/h B. 80,000 Btu/h C. 100,000 Btu/h D. 120,000 Btu/h
D. 120,000 Btu/h
What is the minimum size air-supply duct that must be installed for a 60,000 Btu/h gravity-type furnace? A. 12" x 20" B. 30" x 10" C. 12" x 10" D. 14" x 30"
D. 14" X 30"
According to the Energy Efficiency Standards, what is the ideal indoor temperature during the summer? A. 68°F B. 72°F C. 74°F D. 78°F
D. 78F
The drawing shows a heating equipment closet in a residential basement. Two ventilating grilles are shown. Which of the following statements is correct? A. neither grille is required B. only grille A is required C. only grille B is required D. both grilles are required
D. Both grilles are required
The installation shown in the drawing below is: A. correct B. incorrect: There is a problem with the lines. C. incorrect: There is a problem with the access panel. D. incorrect: There is a problem with the spacing.
D. The probable answer is "D": The condensing unit should be at least 10 ft away from any wall or obstruction that might return heated discharge air to the air intake. However, check the State's drawing carefully.
How far must combustible material be placed from an electric furnace? 3 ft 4 ft 10 ft none of the above
D. There is no clearance requirement because the heat from an electric furnace is not produced by a flame.
If you turn the thermostat up on a heating system and nothing happens, the trouble is likely: A. 0 volts across the limit switch B. 24 volts across the red and white conductors C. 24 volts across the red and common conductors D. blown fuse
D. blown fuse
Material for gas piping must be made of: A. aluminum B. cast iron C. brass that is more than 75% copper D. brass that is less than 75% copper
D. brass that is less than 75% copper
In a thermostat set to cooling mode, if the fan switch is in the ON position, which additional connections must be made when a conventional system calls for cooling? A. red to green B. red to blue C. red to white D. red to yellow
D. red to yellow
An unloader is used to: A. remove freon B. reduce a high head pressure C. disconnect a current D. reduce capacity of compressor
D. reduce capacity of compressor
What does SEER stand for? A. super energized electric resistor B. safety exhaust expansion radiator C. super energy efficiency ratio D. seasonal energy efficiency ratio
D. seasonal energy efficiency ratio
What is the most efficient propane burner flame? A. wavy yellow flame B. soft red flame C. soft blue flame D. soft blue flame with slightly yellow tips
D. soft blue flame with slight yellow tips
Why should there be clearance between an air duct and a rafter?
For fire safety purposes
What color is a cylinder of Freon-22?
Green
A Type I Certification (EPA examination) allows you to service:
Small appliances
To check the delivery of an A/C system, you use: a manometer a velometer a barometer an ohmmeter
a velometer
If you straighten a fin, what is the effect on the coil? airflow increases & coil is more effective airflow increases & coil is less effective airflow decreases & coil is more effective airflow decreases & coil is less effective
airflow increases & coil is more effective
In a forced-air heater, the pilot light comes on, but the main burner does not. Which of the following is the most likely cause? defective main valve restriction in return air system defective limit switch plugged or restricted pilot orifice
defective limit switch
Which material has the least insulating value for a given thickness? glass high density concrete wood stucco
high density concrete
How do you test for humidity? use wet bulb and read chart use dry bulb and read chart use any electrical tester with temperature adapter use an electrical psychrometer
use an electrical psychrometer
