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Air-Conditioning Systems > Thermostats > Flashcards

Thermostats Flashcards

1
Q

A thermostat that remembers set points and adapts system operation and cycles accordingly is a _____ thermostat.

A

learning

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2
Q

The type of HVAC system operation that regulates the increase or decrease of intensity and can result in significant energy usage reduction over time is ____ operation.

A

modulating

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3
Q

The longer a bimetal coil is, the ____.

A

longer it will stretch

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4
Q

A switch used with a bimetal coil that consists of a pair of contacts in a glass tube that changes position based on magnets is a ____ switch.

A

reed

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5
Q

A switch used with a bimetal coil that consists of a glass tube containing wire contacts and a puddle of liquid that changes position based on its physical position is a ____ switch.

A

mercury

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6
Q

The difference between a heating-only thermostat with two wires and heating-only thermostat with three wires is the addition of a ____.

A

holding circuit

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7
Q

Temperature swing is the total difference between ____.

A

high and low temperatures in a room

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8
Q

For a heating thermostat, system lag occurs when temperature ____.

A

drops below the cut-in value

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9
Q

A heat anticipator’s purpose is to switch ____.

A

off the heating system just before reaching the cut-out temperature

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10
Q

Anticipators are basically small —-.

A

resistors

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11
Q

A cooling anticipator’s purpose is to switch ____.

A

on the cooling system just before reaching the cut-in temperature

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12
Q

A cooling anticipator is always installed in ____.

A

parallel with the thermostat switch

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13
Q

The number of wires to connect to a combination thermostat depends primarily on ____.

A

thermostat features and stages of operation

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14
Q

the primary purpose of a multistage thermostat is that it can control an HVAC system’s ____.

A

capacity

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15
Q

To control higher-current loads, a low-voltage thermostat will usually use ____.

A

relays and contactors

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16
Q

The VA rating of a step-down transformer used with thermostats is used to determine _____.

A

secondary side current rating

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17
Q

Low-voltage thermostats wiring for lengths up to 50’ should normally be at least ____.

A

18 AWG

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18
Q

Low-voltage thermostats wiring for lengths over 50’ should normally be at least ____.

A

16 AWG

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19
Q

Millivolt thermostats can only be used in certain ____ systems.

A

heating

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20
Q

The sensing element used in millivolt thermostats in a(n) ____.

A

thermocouple

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21
Q

To operate, a millivolt thermostat depends on a(n) ____.

A

standing pilot light

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22
Q

The electrical load that a millivolt thermostat is used to actuate is a ____.

A

solenoid

23
Q

A thermostat that draws a small amount of power from the low-voltage side of the HVAC system control to operate its electronics is a ____ thermostat.

A

power-stealing

24
Q

Common connection terminal on a thermostat.

A

C

25
Q

Compressor contactor (stage 2) terminal on a thermostat.

A

Y2

26
Q

Condensing unit (compressor) contactor terminal on a thermostat.

A

Y

27
Q

Cooling power terminal on a thermostat.

A

Rc

28
Q

Damper terminal on a thermostat.

A

M1 or DMP

29
Q

Dehumidifier terminal on a thermostat.

A

DHD

30
Q

Fan relay (cooling only) terminal on a thermostat.

A

G

31
Q

Heating power terminal on a thermostat.

A

Rh

32
Q

Heat pump auxiliary heat terminal on a thermostat.

A

Aux/E

33
Q

Heat relay (stage 1) terminal on a thermostat.

A

W

34
Q

Heat relay (Stage 2) terminal on a thermostat.

A

W2

35
Q

Humidifier terminal on a thermostat.

A

HMD

36
Q

Indoor temperature sensor terminal on a thermostat.

A

In or IDT

37
Q

Reversing valve terminal on a thermostat.

A

O/B

38
Q

HVAC system settings are often set and managed using ____ on a circuit board or thermostat subbase.

A

DIP switches

39
Q

Free cooling is a method of cooling a building using a(n) ____.

A

air-side economizer

40
Q

For best results, free cooling should be used on a thermostat that has ____.

A 
enthalpy control  
(outdoor air sensor)
41
Q

When free cooling is used on a forced-air system with mechanical air conditioning, a ____ thermostat must be used.

A

multistage

42
Q

When installing a wireless thermostat, a good location for a temperature sensor would be ____.

A

on an inner wall about 5’ above the floor.

The average location of a normal thermostat.

43
Q

When an HVAC system is set to operate in heating mode, a meter reading should indicate a(n) ____ across terminals R and Y.

A

open circuit

44
Q

When and HVAC system is operating in cooling mode, a meter reading should indicate a(n) ____ across terminals R and W.

A

open circuit

45
Q

When troubleshooting an HVAC system, if no voltage is measured across any of the pairs of thermostat wiring terminals, the problem is most likely with the wire connected to terminal ____.

A

R

46
Q

When troubleshooting a heating system that does not work, if source voltage can be measured in the thermostat, the problem is most likely with the wire connected to terminal ____.

A

W

47
Q

When measuring voltage across an open switch on a thermostat, expect to read ____.

A

source voltage

48
Q

If a heating system turns on once jumpers are placed across the proper wiring terminals in the thermostat, the problem is most likely the ____.

A

wires between thermostat and heating

49
Q

A multistage thermostat will only close its switch to terminal ____ once temperature drops below set point by more than 3 degrees F.

A

W2

50
Q

A multistage thermostat will only close its switch to terminal ____ once temperature rises above set point by more than 3 degrees F.

A

Y2

51
Q

A step-down transformer used with a low-voltage thermostat should not have ____.

A

any electrical loads in series

52
Q

To compare a step-down transformer’s secondary side VA rating with the VA of all the electrical loads in its circuit, a technician must add together each load’s ____.

A

current rating

53
Q

In residential applications, live electrical measurements across terminals in a line-voltage thermostat should be ____.

A

120 Vac or 240 Vac

Air-Conditioning Systems (7 decks)

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