Thermostats Flashcards
A thermostat that remembers set points and adapts system operation and cycles accordingly is a _____ thermostat.
learning
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.
modulating
The longer a bimetal coil is, the ____.
longer it will stretch
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.
reed
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.
mercury
The difference between a heating-only thermostat with two wires and heating-only thermostat with three wires is the addition of a ____.
holding circuit
Temperature swing is the total difference between ____.
high and low temperatures in a room
For a heating thermostat, system lag occurs when temperature ____.
drops below the cut-in value
A heat anticipator’s purpose is to switch ____.
off the heating system just before reaching the cut-out temperature
Anticipators are basically small —-.
resistors
A cooling anticipator’s purpose is to switch ____.
on the cooling system just before reaching the cut-in temperature
A cooling anticipator is always installed in ____.
parallel with the thermostat switch
The number of wires to connect to a combination thermostat depends primarily on ____.
thermostat features and stages of operation
the primary purpose of a multistage thermostat is that it can control an HVAC system’s ____.
capacity
To control higher-current loads, a low-voltage thermostat will usually use ____.
relays and contactors
The VA rating of a step-down transformer used with thermostats is used to determine _____.
secondary side current rating
Low-voltage thermostats wiring for lengths up to 50’ should normally be at least ____.
18 AWG
Low-voltage thermostats wiring for lengths over 50’ should normally be at least ____.
16 AWG
Millivolt thermostats can only be used in certain ____ systems.
heating
The sensing element used in millivolt thermostats in a(n) ____.
thermocouple
To operate, a millivolt thermostat depends on a(n) ____.
standing pilot light
The electrical load that a millivolt thermostat is used to actuate is a ____.
solenoid
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.
power-stealing
Common connection terminal on a thermostat.
C
Compressor contactor (stage 2) terminal on a thermostat.
Y2
Condensing unit (compressor) contactor terminal on a thermostat.
Y
Cooling power terminal on a thermostat.
Rc
Damper terminal on a thermostat.
M1 or DMP
Dehumidifier terminal on a thermostat.
DHD
Fan relay (cooling only) terminal on a thermostat.
G
Heating power terminal on a thermostat.
Rh
Heat pump auxiliary heat terminal on a thermostat.
Aux/E
Heat relay (stage 1) terminal on a thermostat.
W
Heat relay (Stage 2) terminal on a thermostat.
W2
Humidifier terminal on a thermostat.
HMD
Indoor temperature sensor terminal on a thermostat.
In or IDT
Reversing valve terminal on a thermostat.
O/B
HVAC system settings are often set and managed using ____ on a circuit board or thermostat subbase.
DIP switches
Free cooling is a method of cooling a building using a(n) ____.
air-side economizer
For best results, free cooling should be used on a thermostat that has ____.
enthalpy control (outdoor air sensor)
When free cooling is used on a forced-air system with mechanical air conditioning, a ____ thermostat must be used.
multistage
When installing a wireless thermostat, a good location for a temperature sensor would be ____.
on an inner wall about 5’ above the floor.
The average location of a normal thermostat.
When an HVAC system is set to operate in heating mode, a meter reading should indicate a(n) ____ across terminals R and Y.
open circuit
When and HVAC system is operating in cooling mode, a meter reading should indicate a(n) ____ across terminals R and W.
open circuit
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 ____.
R
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 ____.
W
When measuring voltage across an open switch on a thermostat, expect to read ____.
source voltage
If a heating system turns on once jumpers are placed across the proper wiring terminals in the thermostat, the problem is most likely the ____.
wires between thermostat and heating
A multistage thermostat will only close its switch to terminal ____ once temperature drops below set point by more than 3 degrees F.
W2
A multistage thermostat will only close its switch to terminal ____ once temperature rises above set point by more than 3 degrees F.
Y2
A step-down transformer used with a low-voltage thermostat should not have ____.
any electrical loads in series
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 ____.
current rating
In residential applications, live electrical measurements across terminals in a line-voltage thermostat should be ____.
120 Vac or 240 Vac
