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