HVAC - CH 13 - Introduction to Automatic Controls

1. What is one classification of controls discussed, aside from pneumatic? A. Hydraulic B. Sonic C. Electromechanical D. Chemical

C. Electromechanical controls are one of the discussed classifications, alongside electrical, mechanical, electronic or digital, and pneumatic.

2. The automatic control of a system aims to maintain what kind of conditions? A. Fluctuating B. Stable or constant C. Variable D. Unpredictable

B. Automatic control is intended to maintain stable or constant conditions.

3. True or False: Human interference is often excessive in systems with automatic controls. A. True B. False

B. False. Automatic control aims to maintain conditions without excessive human interference.

4. A system using automatic controls must regulate itself within which specific boundaries? A. Maximum operating B. Emergency C. Design D. Tolerance

C. The system must regulate itself within the design boundaries that have been established.

5. What can result if equipment is allowed to operate outside of its design boundaries? A. Increased efficiency B. System component damage C. Reduced maintenance D. Enhanced comfort

B. System components may become damaged if equipment operates outside design boundaries.

6. Besides equipment damage, what human aspect can be sacrificed if a system operates outside its design boundaries? A. Productivity B. Comfort C. Safety D. Communication

B. Human comfort may be sacrificed if a system operates outside its design boundaries.

7. In extreme cases, operating equipment outside design boundaries can lead to what severe consequence? A. Property loss B. Personal injury C. Energy waste D. Noise pollution

B. In extreme cases, personal injury can result.

8. What is a main purpose of the HVACR industry concerning conditions? A. To forecast weather patterns B. To control space or product conditions C. To design architectural structures D. To manage utility grids

B. The main purpose of the HVACR industry is to control space or product conditions.

9. Which of the following is an important factor controlled by the HVACR industry? A. Ground temperature B. Air quality C. Water purity D. Solar radiation

B. Air quality is one of the important factors controlled, along with temperature, humidity, air movement, and air cleanliness.

10. Controls can be classified as either operational devices or what other type of device? A. Regulating B. Monitoring C. Safety D. Adjustment

C. Controls can be classified as either operational devices or safety devices.

11. What is the function of operational devices and controls? A. To initiate system shutdown B. To maintain the normal operating conditions of a system C. To override safety protocols D. To diagnose system failures

B. Operational devices and controls function to maintain the normal operating conditions of a system.

12. A cooling thermostat serves as an example of which type of control? A. Safety B. Manual C. Operational D. Emergency

C. A cooling thermostat is an example of an operational control.

13. When the space temperature rises above the preset temperature, what action does a cooling thermostat take? A. It opens its contacts to de-energize the cooling system. B. It closes its contacts to energize the cooling system. C. It sounds an alarm. D. It switches to a heating cycle.

B. When the space temperature rises above the preset temperature, the thermostat will close to energize the cooling system.

14. True or False: Safety devices are intended to open and close during normal system operation. A. True B. False

B. False. Safety devices are not intended to open and close during normal system operation.

15. What is the typical state of safety devices during proper system operation? A. Normally open B. Normally closed C. Intermittently open D. Continuously cycling

B. Safety devices are typically normally closed and will remain closed as long as the system is operating properly.

16. What is one item in the HVACR field that needs to be controlled by automatic controls? A. The color of components B. The flow of electricity through circuits C. The structural integrity of buildings D. The material composition of ducts

B. The flow of electricity through circuits is one item that needs to be controlled.

17. Modulating controls are used to vary the speed of what component? A. A compressor motor B. A blower motor C. A fan coil unit D. A refrigeration pump

B. Modulating controls are used to vary the speed of a blower motor.

18. What is the primary method automatic controls in the HVACR industry usually provide? A. Water purification B. Humidity removal C. Temperature control D. Air filtration

C. Automatic controls in the HVACR industry usually provide some method of controlling temperature.

19. When a control is used to protect equipment from damaging itself, what is it known as? A. A thermostat B. A safety device C. An operational control D. A manual switch

B. When used to protect equipment, the control is known as a safety device.

20. A household refrigerator maintains the fresh food section temperature at approximately what degrees Fahrenheit? A. 25°F B. 35°F C. 45°F D. 55°F

B. The refrigerator maintains the space temperature in the fresh food section at about 35°F.

21. Which type of food, if frozen, is mentioned as not being edible after the fact? A. Potatoes B. Apples C. Lettuce D. Carrots

C. Foods such as eggs, tomatoes, and lettuce are not edible after being frozen.

22. What device automatically stops and starts the refrigeration cycle in a refrigerator to maintain the desired temperature? A. An overload B. A pressure switch C. A thermostat D. A circuit breaker

C. The thermostat automatically stops and starts the refrigeration cycle to maintain the box at the desired temperature.

23. What protective device keeps the compressor in a refrigerator from overloading and damaging itself? A. A fuse B. An overload C. A thermistor D. A thermocouple

B. The compressor in the refrigerator has a protective device called an overload that keeps it from overloading and damaging itself.

24. True or False: An overload control typically opens its contacts to allow the compressor to operate when an overload occurs. A. True B. False

B. False. An overload control is designed to open its contacts and prevent the compressor from operating.

25. What is an example scenario where a refrigerator overload control would activate? A. When the power goes off and comes right back on while the refrigerator is running. B. When the refrigerator is first plugged in after installation. C. When the door is left open for an extended period. D. When the defrost cycle begins.

A. One such example would be when the power goes off and comes right back on while the refrigerator is running.

26. Overloading often occurs when a refrigerator's low-torque, fractional-horsepower compressor motor tries to start against what condition? A. High ambient temperature B. Unequal system pressures C. A restricted evaporator coil D. Low voltage supply

B. Overloading often occurs when the refrigerator’s low-torque, fractional-horsepower compressor motor tries to start against unequal system pressures.

27. What electrical phenomenon does the motor draw when overloading occurs due to starting against unequal system pressures? A. Rated running amperage B. Locked rotor amperage C. Starting capacitor current D. Inductive reactive power

B. When this happens, the motor will draw locked rotor amperage.

28. After an overload control opens the electrical circuit, what period does the compressor typically go through before the control resets? A. A warm-up period B. A high-pressure period C. A cool-down period D. A diagnostic period

C. After the compressor goes through a cool-down period, the control resets.

29. What condition must be nearing equalization for the compressor motor to start safely after an overload? A. Ambient temperatures B. System pressures C. Refrigerant volume D. Electrical current

B. The control resets and closes the circuit when, hopefully, system pressures are nearing equalization and the motor can start safely.

30. What type of system overload occurs due to a short circuit or improper electrical connections? A. Thermal B. Mechanical C. Electrical D. Chemical

C. An electrical overload happens due to an electrical problem such as a short circuit, improper electrical connections, or a faulty electrical component.

31. A thermal system overload may occur if a specific electrical or mechanical component is not cooled properly, leading to what outcome? A. Underheating B. Overheating C. Reduced resistance D. Increased fluid flow

B. A thermal system overload may occur if a specific electrical or mechanical component is not cooled properly, resulting in overheating.

32. What might cause a mechanical system overload by requiring the compressor motor to work harder, producing excess current and heat? A. Overcharged refrigerant B. Restricted airflow through a condensing coil C. Dirty air filter in the return duct D. Leaking evaporator coil

B. Restricted airflow through a condensing coil of a central air conditioner would produce high head pressure, requiring the compressor motor to work harder.

33. Where is a small heater located in a combination overload control? A. Inside the compressor motor windings B. Under the bimetallic element of a compressor overload control C. On the discharge line of the compressor D. Within the control panel housing

B. A small heater is located under the bimetallic element of a compressor overload control.

34. What effect does the heater have on the bimetallic element in a combination overload control when an overload occurs? A. It cools the element. B. It causes the element to straighten. C. It warps the bimetallic element and opens the circuit. D. It magnetizes the element.

C. When either an electrical or thermal overload occurs, the heater warps the bimetallic element and opens the circuit.

35. Which of the following is listed as a common automatic control device? A. Traffic lights B. Water heater temperature controls C. Automobile braking systems D. Home security alarms

B. Water heater temperature controls are listed as a common automatic control device.

36. True or False: Fuses and circuit breakers are examples of automatic controls that manage current flow in home electric circuits. A. True B. False

A. True. Fuses and circuit breakers that control current flow in home electric circuits are listed as common automatic control devices.

37. Automatic controls in the air-conditioning and refrigeration industry primarily monitor what physical property? A. Pressure B. Humidity C. Temperatures D. Air velocity

C. Automatic controls in the air-conditioning and refrigeration industry monitor temperatures.

38. Some controls monitoring electrical overloads sense temperature changes in what specific part of a system? A. Fluid lines B. Wiring circuits C. Compressor housing D. Air ducts

B. Some controls that respond to temperature changes are used to monitor electrical overloads by sensing temperature changes in the wiring circuits.

39. What is the most common device used to detect thermal change? A. Thermocouple B. Thermistor C. Bimetal device D. Pressure transducer

C. The bimetal device is probably the most common device used to detect thermal change.

40. In its simplest form, a bimetal device consists of two unlike what, attached back to back? A. Wires B. Magnets C. Metal strips D. Springs

C. In its simplest form, it consists of two unlike metal strips—often brass and steel—attached back to back.

41. What is one example of the two metals commonly used in a bimetal strip? A. Copper B. Steel C. Aluminum D. Gold

B. Steel is one example, often paired with brass.

42. When a bimetal device is heated, which metal typically expands faster, causing the device to warp? A. Steel B. Brass C. Aluminum D. Copper

B. When the device is heated, the brass expands faster than the steel, which causes the device to warp.

43. The motion of a bimetal strip can be used to perform what type of useful task? A. Generate light B. Produce sound C. Stop, start, or modulate electrical current or fluid flow D. Convert energy into mechanical force only

C. The motion of the bimetal strip is then used to perform some useful task, such as to stop, start, or modulate electrical current or fluid flow.

44. What limits the application of bimetal controls? A. Their cost B. The amount of warp that can be accomplished with a temperature change C. Their durability D. Their response time

B. Bimetal controls are limited in application by the amount of warp that can be accomplished with a temperature change.

45. To make bimetal devices practical over a wider temperature range, how is the strip typically lengthened? A. By welding additional pieces B. By coiling it into a circle C. By thinning the metal D. By adding insulation

B. A longer strip is normally coiled into a circle, shaped like a hairpin, wound into a helix, or formed into a worm shape.

46. A bimetal strip lengthened into a helix shape allows for what? A. Reduced sensitivity B. Increased warp over a wider temperature range C. Manual adjustment only D. Conversion to a different control type

B. Lengthening the strip, such as into a helix, increases the amount of bend, making it practical over a wider temperature range.

47. The movable end of a coiled bimetal device can be attached to what to indicate temperature? A. A dial B. A pointer C. A scale D. A light

B. The movable end of the coil or helix can be attached to a pointer to indicate temperature.

48. True or False: The rod and tube control relies on a single metal's expansion rate to detect temperature changes. A. True B. False

B. False. The rod and tube is another type of control that uses two dissimilar metals that react differently to changes in temperature.

49. In a rod and tube device, which component typically has a high expansion rate? A. The internal rod B. The outer tube C. The connecting linkage D. The pivot point

B. It has an outer tube of metal with a high expansion rate and an internal rod of metal with a low expansion rate.

50. The rod and tube could be more accurately called what? A. "Rod in rod" B. "Tube on rod" C. "Rod in tube" D. "Tube and rod"

C. The rod and tube could more accurately be called the “rod in tube.”

51. For what common residential appliance has the rod and tube device been used for years to sense water temperature? A. Washing machines B. Dishwashers C. Gas water heaters D. Refrigerators

C. Used for years in residential gas water heaters, the tube, which is inserted into the tank, provides very accurate sensing of water temperature.

52. In a rod and tube control for a gas water heater, what does the tube push to start or stop the heating of water? A. The thermostat B. The gas valve C. The igniter D. The flue damper

B. As the tank water temperature changes, the tube pushes the rod and opens or closes the gas valve to start or stop the heating of the water in the tank.

53. What type of valves use a small heater wrapped around the tube portion of a rod and tube mechanism? A. Solenoid valves B. Ball valves C. Heat motor valves D. Check valves

C. Heat motor valves are another application of the rod and tube device.

54. In a heat motor valve, what happens when voltage is applied to the small heater? A. The tube shrinks and closes the valve. B. The tube heats up and expands, which pulls the rod and opens the valve. C. The rod contracts and pushes the valve closed. D. The heater cools, causing the tube to contract.

B. When voltage is applied, the tube heats up and expands, which pulls the rod and opens the valve for water flow.

55. What common application for the rod and tube type of control is mounted to the return duct of an air-conditioning system? A. A pressure switch B. A humidity sensor C. A duct-mounted limit control D. An airflow sensor

C. Another common application for the rod and tube type of control is in a duct-mounted limit control.

56. In the event of a fire, a duct-mounted limit control using a rod and tube device will prevent what component from operating if the return air temperature gets too high? A. The compressor B. The condenser fan C. The air-conditioning system's blower D. The heating element

C. This type of device will “lock out” or prevent an air-conditioning system’s blower from operating in the event the return air temperature gets too high, such as when there is a fire.

57. True or False: A duct-mounted limit control automatically resets once the problem that caused it to trip has been resolved. A. True B. False

B. False. When used in this manner, the device will need to be manually reset once the problem has been identified and resolved.

58. The snap-disc is a type of what other temperature-sensing device? A. Thermocouple B. Thermistor C. Bimetal device D. Fluid-filled control

C. The snap-disc is another type of bimetal device used to sense temperature changes in some applications.

59. What characteristic gives the snap-disc its quick open-and-close feature? A. Its electrical resistance B. Its magnetic properties C. Its snap characteristic D. Its fluid expansion

C. This control is treated separately from the bimetal because its snap characteristic gives it a quick open-and-close feature.

60. What feature should be incorporated into all controls that stop and start electrical loads to enhance their lifespan? A. A manual override B. Some sort of snap-action feature C. A visual indicator D. An audible alarm

B. Some sort of snap-action feature should be incorporated into all controls that stop and start electrical loads.

61. What occurs when an electric circuit is closed or opened, especially when opened, that snap action helps to mitigate? A. A power surge B. An electrical arc C. A voltage drop D. A current spike

B. When an electric circuit is closed or opened, but especially when opened, an electrical arc occurs.

62. What is a small version of an electric welding arc that occurs when electrons try to keep flowing after a switch is opened? A. A short circuit B. An electrical arc C. A static charge D. A resistance drop

B. Electrons are flowing and will try to keep flowing when the switch is opened, creating the arc.

63. True or False: The slower the opening of an electrical switch, the longer the switch will last. A. True B. False

B. False. The faster the opening, the longer the switch will last.

64. What is one type of mechanism some switches use to accelerate the opening action? A. A spring-loaded mechanism B. An over-center device C. A pneumatic cylinder D. A hydraulic piston

B. Some switches use an over-center device to accelerate the opening.

65. What substance is mentioned that some snap-action switches may use to create quick action? A. Oil B. Water C. Mercury D. Alcohol

C. Some use a puddle of mercury to create the quick action.

66. What method, besides bimetal devices, is described for sensing temperature change? A. Sound wave reflection B. Fluid expansion C. Light spectrum analysis D. Electromagnetic induction

B. Fluid expansion is another way to sense temperature change.

67. A thermometer can be described as a column of temperature-sensitive liquid rising and falling within what component? A. A bulb B. A hollow stem C. A Bourdon tube D. A bellows

B. A thermometer, for example, can be described as a column of temperature-sensitive liquid rising and falling within a hollow stem.

68. What happens to the volume of liquid in a thermometer as its temperature changes? A. It remains constant. B. The volume of the liquid will change in response. C. It decreases only. D. It expands only.

B. As the temperature of the liquid changes, the volume of the liquid will change in response.

69. What are the lines or tubes called that transmit signals indicating a temperature change in fluid expansion controls? A. Capillary tubes B. Conduction lines C. Transmission lines D. Sensing conduits

C. The lines or tubes that transmit these signals are referred to as transmission lines.

70. What device is a thin, flexible metal disc, typically steel, with a large area, that generates usable motion from expanding liquid? A. A bellows B. A diaphragm C. A Bourdon tube D. A thermistor

B. One such device is the diaphragm, which is a thin, flexible metal (typically steel) disc with a large area.

71. True or False: Pressure changes underneath a diaphragm cause it to flex up and down. A. True B. False

A. True. Pressure changes underneath the disc cause it to flex up and down.

72. For more accurate control at the actual bulb location, what kind of bulb is used with a diaphragm? A. A solid-filled bulb B. A partially filled bulb with a liquid that will boil and make a vapor C. An air-filled bulb D. A vacuum-sealed bulb

B. More accurate control at the actual bulb location is achieved by using a bulb partially filled with a liquid that will boil and make a vapor.

73. In a partially filled bulb system, which is more sensitive to temperature change? A. The vapor B. The liquid C. The transmission line D. The diaphragm

B. The liquid is much more sensitive to temperature change than the vapor that is used to transmit the pressure.

74. For an R-134a walk-in refrigerated box example, at what temperature does the system shut off? A. 25°F B. 35°F C. 45°F D. 55°F

B. The box temperature is maintained by shutting the refrigeration system off when its temperature reaches 35°F.

75. When the R-134a walk-in refrigerated box temperature reaches 35°F, what is the corresponding pressure for R-134a? A. 20 psig B. 30 psig C. 40 psig D. 50 psig

B. At the point that the unit needs to be cycled off, the bulb temperature is 35°F, which corresponds to a pressure of 30 psig for R-134a.

76. What is the pressure inside the control when the cooler temperature in the R-134a example rises to 45°F and it is time to restart the unit? A. 30 psig B. 35 psig C. 40 psig D. 45 psig

C. When the cooler temperature rises to 45°F, the pressure inside the control is 40 psig and it is time to restart the unit.

77. What characteristic describes the diaphragm's power during its movement? A. Limited B. Great deal of power C. Variable D. Insignificant

B. A diaphragm travels a limited amount but has a great deal of power during its movement.

78. When more travel is needed in a fluid expansion control, what accordion-like device can be used? A. A diaphragm B. A capillary tube C. A bellows D. A Bourdon tube

C. When more travel is needed, another device, called a bellows, can be used. The bellows is much like an accordion.

79. True or False: A bellows normally uses liquid inside instead of vapor for its operation. A. True B. False

B. False. Normally, the bellows is used with a vapor inside instead of a liquid.

80. What device, used similarly to a diaphragm and bellows, monitors fluid expansion to indicate temperature by straightening out with increased vapor pressure? A. A thermistor B. A thermocouple C. A Bourdon tube D. A snap-disc

C. The Bourdon tube is used in the same manner as the diaphragm and the bellows to monitor fluid expansion, in this case to indicate temperature.

81. Controls employing partially filled bulbs are described as what, due to their long history in the industry? A. Complex B. Expensive C. Unreliable D. Reliable, simple, and economical

D. Controls employing partially filled bulbs are widely used in the industry because they are reliable, simple, and economical.

82. What does the thermocouple use to control thermal change, instead of expansion? A. Chemical reactions B. Magnetic fields C. Electrical principles D. Mechanical linkages

C. The thermocouple does not use expansion to control thermal change; instead, it uses electrical principles.

83. What is a thermocouple composed of at one joined end? A. Two identical metals B. Two unlike metals C. A single metal with a coil D. A bimetallic strip

B. The thermocouple consists of two unlike metals joined together at one end.

84. What are two common metals mentioned that thermocouple wires are often made of? A. Copper and aluminum B. Iron and constantan C. Brass and steel D. Nickel and chromium

B. It usually consists of wire made of unlike metals such as iron and constantan.

85. When a thermocouple is heated on its fastened end, what is started due to the temperature difference between its two ends? A. A chemical reaction B. An electrical current flow C. A mechanical movement D. A magnetic field

B. When heated on the fastened end, an electrical current flow is started due to the temperature difference between the two ends of the device.

86. What are the two junctions of a thermocouple called? A. Primary and secondary B. Hot and cold C. Input and output D. Source and drain

B. Each thermocouple has a hot junction and a cold junction.

87. True or False: The cold junction of a thermocouple reaches a higher temperature than the hot junction. A. True B. False

B. False. The hot junction, as the name implies, reaches a higher temperature than the cold junction.

88. The difference in what physical property between the hot and cold junctions is what starts the current flowing in a thermocouple? A. Pressure B. Humidity C. Temperature D. Volume

C. This difference in temperature is what starts the current flowing.

89. How does heat cause electrical current to flow in the two metals of a thermocouple? A. In the same direction in both metals. B. In one direction in one metal and in the opposite direction in the other. C. Only in the hotter metal. D. Only when a magnet is applied.

B. Heat will cause an electrical current to flow in one direction in one metal and in the opposite direction in the other.

90. For safety purposes, thermocouples have been used extensively in gas furnaces to detect what? A. Gas leaks B. Pilot light flame C. Carbon monoxide levels D. Flue gas temperature

B. The thermocouple has been used extensively for years in gas furnaces for safety purposes to detect the pilot light flame.

91. Which type of pilot system, mostly not being produced anymore, worked best with thermocouple pilot light applications? A. Intermittent pilot systems B. Direct spark ignition systems C. Standing pilot systems D. Hot surface ignition systems

C. This application is found on older pieces of equipment, since it works best with standing pilot systems, which are, for the most part, not being produced anymore.

92. What is the approximate output voltage of pilot-light thermocouples? A. 120 volts AC B. 24 volts AC C. 20 to 30 millivolts DC D. 500 millivolts AC

C. Pilot-light thermocouples have an output voltage of about 20 to 30 millivolts (DC).

93. What is the name for multiple thermocouples wired in series with each other to provide a higher output voltage? A. Thermistors B. Rectifiers C. Thermopiles D. Transducers

C. Multiple thermocouples can be wired in series with each other to provide a higher output voltage and, when configured like this, are called thermopiles.

94. What is the approximate power supply voltage of a thermopile used as the only power source on some gas-burning equipment? A. 20 millivolts B. 50 millivolts C. 200 millivolts D. 500 millivolts

D. The power supply is very small (about 500 millivolts).

95. Beyond gas equipment, thermopiles have also been used in remote areas to operate what devices, using the sun or heat from a small fire? A. Televisions B. Radios C. Computers D. Refrigerators

B. The thermopile has also been used in remote areas to operate radios using the sun or heat from a small fire.

96. What single component has significantly changed the landscape of electronic temperature-sensing devices in the HVACR industry? A. The capacitor B. The resistor C. The thermistor D. The transistor

C. The single component that has changed the face of electronic temperature-sensing devices is the thermistor.

97. How does a thermistor primarily vary its resistance to current flow? A. Based on pressure B. Based on humidity C. Based on its temperature D. Based on voltage fluctuations

C. The thermistor varies its resistance to current flow based on its temperature.

98. True or False: Thermistors are typically incorporated into mechanical control boards. A. True B. False

B. False. Thermistors are incorporated into solid-state circuit boards.

99. What can special electronic circuits, which monitor changes in current flow in a thermistor, provide? A. A mechanical override B. A temperature readout C. A pressure measurement D. A humidity adjustment

B. The changes in current flow in the device are monitored by special electronic circuits that can stop, start, and modulate machines or provide a temperature readout.

100. What is one of the materials from which thermistors are usually made? A. Platinum B. Cobalt oxide C. Silver D. Copper

B. Thermistors are usually made of cobalt oxide, nickel, or manganese and from a few other materials.