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47 Cards in this Set
- Front
- Back
- 3rd side (hint)
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two main categories of thermally operated controls |
solid and fluid expansion |
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what is the principle of operation of a rod and tube thermostat used on a hot water heater? |
the tube expands and contracts but the rod does not |
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what is an advantage of a rod and tube thermostat? |
-the control is inexpensive to operate -mechanical rigidity -excellent operating results |
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what is the principle of operation of a fluid expansion thermostat? |
the fluid expands when heated and closed the valve |
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what is one advantage of using a liquid bulb thermostat? |
the control may be remotely mounted |
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what is the purpose of a bypass on a modulating gas valve? |
it keeps a small stable flame to the burner |
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what procedure should be followed for leak-testing gas controls? |
apply soapy water to the suspected leak |
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what is the most common type of thermostat used in a residential setting? |
mercury contacts |
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what is the minimum gauge of wire that should be used to connect a thermostat to a control circuit? |
18 gauge |
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what is the importance of the terminal identified as R in a thermostat. |
the terminal sends power to the thermostat |
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what is the importance of a heat anticipator in a room thermostat? |
shortens the time a gas valve is on. |
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how is a heat anticipator wired to the thermostat contacts? |
in series with the thermostat contacts |
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how is the setting of a heat anticipator determined? |
it is set to the amperage of the control circuit |
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what position are the fan/limit control switch contacts in when the furnace is on standby |
the fan switch is open and the limit is closed |
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in a standard furnace, which control normally shares its sensing element with the high-temperature limit control? |
the fan control |
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what is the most important factor in replacing a combination fan/limit control? |
the volt-amp rating of the control |
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maximum allowable setting for a limit control on a forced air furnace? |
250°F |
same as a high limit |
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how is a safety gas valve installed into the piping and wired to a system powered by a thermopile |
piped in series wired in parallel |
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what is the purpose of an ECO |
to act as a manual reset high-temperature limit controls |
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what is the operating principle of a diaphragm gas valve? |
the valve operates by diverting gas pressure to the top of the diaphragm. |
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in what positions should a diaphragm gas valve be installed |
in horizontal pipe with the gas valve head vertical |
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what would happen to a diaphragm gas valve if the bleed port was blocked? |
the valve would not open |
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how should a solenoid gas valve be installed? |
in a horizontal pipe with the valve head vertical |
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what is the principle of operation for a solenoid gas valve? |
a coil becomes a magnet and raises the valve disc |
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what is the importance of a redundant gas valve? |
has one solenoid valve and one diaphragm valve for safety |
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how far must an Engery cut-off switch be off a hot water tank? |
6" |
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when setting a limit control, how much higher should it be set on the fan? |
20°F |
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where is a solenoid gas valve installed? |
on the burner manifold and must be installed downstream of the 100% shut off valve |
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what appliance would you find a solid expansion control? |
HWT |
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what appliance would you find a fluid expansion control on? |
a boiler |
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what may cause vapour expansion to differ? |
the effects of altitude or atmospheric pressure |
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what does the sensing element do in a rod and tube thermostat? |
reacts to the change in temperature |
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what does the operating element do in a rod and tube thermostat? |
controls the volume of gas flowing to the burner |
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can liquid be compressed? |
no |
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what is a thermostatic gas valve also know as? |
modusnap valve |
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where are thermostatic gas valves installed? |
on the appliances burner maifold |
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what are room thermostats not connected to? and why? |
to a load as it will burn out the heat anticipator |
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what does W mean when wiring? |
heating |
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what does G mean when wiring? |
Fan |
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what does Y mean when wiring? |
Cooling |
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what does C mean when wiring? |
Common |
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what is the max temperature for a limit control? |
250°F |
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what is the recommended setting for a limit control? |
180°F to 200°F |
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what is the limit control temperature setting for a gravity furnace? |
350°F |
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how are thermostats wired? |
in series |
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is a solenoid gas valve considered to be a load? |
yes |
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what does this symbol represent? |
solenoid gas valve |
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