Unit 52 Gas Furnace Controls Exam
Questions and Answers 100% Pass
Which of the following is true of the fan switch? - ✔✔Modern fan switches cycle the fan
based on time.
What is the purpose of the limit switch? - ✔✔It prevents overheating by interrupting
the circuit to the gas valve.
Combination gas valves used standing pilot furnaces combine? - ✔✔Pressure
regulation, automatic gas control, and pilot safety.
What is a redundant gas valve? - ✔✔A gas valve with two valves mechanically in series.
What is a draft pressure switch? - ✔✔A switch that senses when the vent is in a draft
condition.
What is the purpose of the door switch on a furnace? - ✔✔To prevent circulation of
combustion products in the house.
What does the furnace board do on most modern furnaces? - ✔✔Controls the ignition,
safety, and blower operation.
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, If pulsed DC current is not present in the flame rod, what is the effect on the gas valve
in a direct spark-ignition system? - ✔✔The valve will remain closed.
What is the purpose of a flame-proving device in a system with a standing pilot? - ✔✔It
shuts off the gas flow in case the pilot goes out.
What safety function does the limit switch perform? - ✔✔It prevents the furnace from
overheating.
What type of flame proving do direct spark ignition controls use? - ✔✔Flame
rectification.
How does the flame rod sense the flames in a flame rectification circuit? - ✔✔The flame
changes the AC voltage to pulsed DC current.
The burner assembly and furnace cabinet should be grounded for safety and because? -
✔✔Most control boards for direct spark ignition or hot surface igniters will not operate
correctly unless the unit is grounded.
Why do direct spark ignition systems use flame rectification for flame safety? -
✔✔Flame rectification is much faster than anything that relies on heat.
The flame rod in DSI furnaces is? - ✔✔A steel rod with a ceramic insulator.
What is a gas pilot light? - ✔✔A small flame that is used to light the main burners.
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Questions and Answers 100% Pass
Which of the following is true of the fan switch? - ✔✔Modern fan switches cycle the fan
based on time.
What is the purpose of the limit switch? - ✔✔It prevents overheating by interrupting
the circuit to the gas valve.
Combination gas valves used standing pilot furnaces combine? - ✔✔Pressure
regulation, automatic gas control, and pilot safety.
What is a redundant gas valve? - ✔✔A gas valve with two valves mechanically in series.
What is a draft pressure switch? - ✔✔A switch that senses when the vent is in a draft
condition.
What is the purpose of the door switch on a furnace? - ✔✔To prevent circulation of
combustion products in the house.
What does the furnace board do on most modern furnaces? - ✔✔Controls the ignition,
safety, and blower operation.
Brittie Donald, All Rights Reserved © 2025 1
, If pulsed DC current is not present in the flame rod, what is the effect on the gas valve
in a direct spark-ignition system? - ✔✔The valve will remain closed.
What is the purpose of a flame-proving device in a system with a standing pilot? - ✔✔It
shuts off the gas flow in case the pilot goes out.
What safety function does the limit switch perform? - ✔✔It prevents the furnace from
overheating.
What type of flame proving do direct spark ignition controls use? - ✔✔Flame
rectification.
How does the flame rod sense the flames in a flame rectification circuit? - ✔✔The flame
changes the AC voltage to pulsed DC current.
The burner assembly and furnace cabinet should be grounded for safety and because? -
✔✔Most control boards for direct spark ignition or hot surface igniters will not operate
correctly unless the unit is grounded.
Why do direct spark ignition systems use flame rectification for flame safety? -
✔✔Flame rectification is much faster than anything that relies on heat.
The flame rod in DSI furnaces is? - ✔✔A steel rod with a ceramic insulator.
What is a gas pilot light? - ✔✔A small flame that is used to light the main burners.
Brittie Donald, All Rights Reserved © 2025 2
