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Controls [FINALIZED!] > [D2L] Final Exam > Flashcards

[D2L] Final Exam Flashcards

1
Q

What does a pressure switch do in a furnace?

1) opens if refrigerant pressure gets too low turning off the compressor
2) closes based on a negative pressure energizing the gas valve
3) Centrifugal switch closes at 10% of motor speed
4) closes when the blower runs proving air flow across the heat exchanger

A

closes based on a negative pressure energizing the gas valve

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2
Q

What is the purpose of the inducer in a furnace?

A

cause fresh air to be brought in for combustion and exhaust the flue gas

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3
Q

What is the switching action of a fan cycling controller on a condenser?

A

Close on rise of pressure, Direct acting

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4
Q

Where is an averaging element often used?

A

Across a heating coil in a duct

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5
Q

What is an example of an analog output signal?

A

a pneumatic tstat

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6
Q

What is a bimetal element?

1) two metals with different coefficients of ductility bonded together
2) two metals with different coefficients of malleability bonded together
3) two metals with different coefficients of thermal expansion bonded together

A

two metals with different coefficients of thermal expansion bonded together

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7
Q

What state is a high limit controller typically in?

A

normally closed

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8
Q

What is a low limit controller used for?

A

interrupt the system operation if the condition drops below the desired value

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9
Q

What is an Oil Failure Pressure control (OFC)?

A

A differential pressure control

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10
Q

What is the Differential?

A

The difference in the values of a controllers on and off set points

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11
Q

What is an example of an open loop?

A

a kitchen faucet

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12
Q

What is a flow switch used to control?

A) Water
B) Air
C) Fluid flow
D) All of the above

A

All of the above

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13
Q

In a MUA, the modulating gas valve delivers gas to the burner, increasing the discharge air temp. The “flow of natural gas” is also known as the…

A

Manipulated Variable

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14
Q

In a MUA, the modulating gas valve delivers gas to the burner, increasing the discharge air temp. The “natural gas” is also known as the…

A

Control Agent

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15
Q

What type of control system are relays and contactors considered?

A

electromechanical

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16
Q

A compressor rated for 20 Amps will require a relay to control it

T or F

A

False

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17
Q

On a call for cooling in a furnace, R to Y closes in the thermostat which also sends power to G

T or F

A

True

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18
Q

The Relays we wired up in class were single pole, single throw

A

False, single pole-double throw

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19
Q

What part of a contactor is not replaceable?

A

body

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20
Q

What type of control is used to delay or pause in the activation and deactivation of a circuit?

A

time delay

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21
Q

What type is a timer?

A) electromechanical
B) electronic
C) thermostat
D) both a and b

A

both a & b

electromechanical
electronic

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22
Q

What device is used to protect end use devices only?

A

Overload device

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23
Q

What is the most important factor with regards to piping design in low temperature applications?

A

compressor oil return

24
Q

A crankcase heater helps reduce refrigerant migration and oil frothing on start up

A

True

25
Q

How is compressor short cycling reduced?

A

Delay on break timer

26
Q

What does DTC stand for?

A

defrost time clock

27
Q

A timer motor in a time clock is powered at all times

A

True

28
Q

What pressure should a pump out cycle shut the compressor off?

A

Just above 0 psig usually set at 2-5 psig

29
Q

Refrigerant boiling out of the oil in a compressor crankcase can cause a system to short cycle

A

True

30
Q

Why are electrical thermostats preferred over electromechanical?

1) more reliable
2) auto-changeover functions
3) more accurate
4) all of the above

A

all of the above

31
Q

What is a high limit control used for in a residential furnace?

A

shut off gas valve if heat exchanger becomes to hot

32
Q

If the differential is set too small on a fan cut in cut out switch, what will happen to the device its controlling?

A

short cycling

33
Q

An old residential furnace fan limit controller has set points of 120F, 140F, and 180F. If the helix bi-metal heats up to 210F what will be energized?

A

The blower

34
Q

What is a manual reset on a high pressure switch?

A

If the unit trips on high pressure it will need to be physically reset

35
Q

What temperature (SDT) should a high pressure switch be set to?

A

135F

36
Q

Cut–out on a low pressure control is set by?

A

cut-in minus differential

37
Q

What does an OFC protect?

A

Compressor running without oil

38
Q

What is a heat exchanger an example of?

A

process plant

39
Q

What is the actuator in a closed loop furnace system?

A

gas valve solenoid

40
Q

If the thermostat is calling for cooling and you read 24v between R and Y which component is running?

A

Nothing, should read 0v

41
Q

If you read 0V between R and Y which components should be running?

1) Blower
2) Nothing
3) Cooling
4) Heating
5) Both a and c

A

Both A & C

Blower
Cooling

42
Q

Furnace will be heating if 24v is measured across R and W

T or F

A

False, it should read 0v

43
Q

What kind of control(s) do most RTU (roof top unit) use?

1) Electronic
2) Electromechanical
3) Both

A

Both

44
Q

What position should a heating zone valve be in the event of a power outage?

A

open, heated water flowing

45
Q

On a typical high efficient furnace what comes after the thermostat closes R to W?

A

Inducer motor comes on (pre-purge)

46
Q

Is an Economizer Analog or Digital?

A

Analog

47
Q

Which BAS is the most current system?

A

Distributed direct digital control system

48
Q

What is the demand on an analog control receiving a 8vdc from a 2-10vdc control system

A

75%

49
Q

Is a Thermostat in heating mode Direct acting or Reverse acting?

A

Reverse, cooling is direct acting

50
Q

In order to produce a smaller differential of temperature, this type of control activates earlier than it would otherwise activate

A

anticipator

51
Q

What is the purpose of a restrictor in a pneumatic system?

A

restrict the buildup of pressure in the branch line

52
Q

One similarity between a 3 pipe controller and a unitary controller is…

A

They are typically hidden in a cabinet

53
Q

Which Device would interrupt the current flow on the control circuit side, which would cause a contactor coil to be deenergized, turning off a motor?

A

Pilot Duty

54
Q

A very sensitive thermal device which resistance responds proportionally to the temperature. As temp increases, its resistance increases

A

RTD (Resistive Temperature Device)

55
Q

The difference between the highest and lowest values the user can set the controller

A

Controller span

56
Q

What does the thermostat do in our blue bin system?

A

energizes the solenoid

Controls [FINALIZED!] (19 decks)

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