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Unit 50 Gas Furnace Controls With Complete Solutions 100% 2024/2025
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Unit 50 Gas Furnace Controls With Complete Solutions 100% 2024/2025
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Unit 50 Gas Furnace Controls WithComplete Solutions 100% 2024/2025
Which of the following is true of the fan switch? Answer: Modern fan switches cycle the fan based
on time.
What is the purpose of the limit switch? Answer: It prevents overheating by interrupting the circuit
to the gas valve.
Combination gas valves used standing pilot furnaces combine? Answer: Pressure regulation,
automatic gas control, and pilot safety.
What is a redundant gas valve? Answer: A gas valve with two valves mechanically in series.
What is a draft pressure switch? Answer: A switch that senses when the vent is in a draft condition.
What is the purpose of the door switch on a furnace? Answer: To prevent circulation of combustion
products in the house.
What does the furnace board do on most modern furnaces? Answer: Controls the ignition, safety,
and blower operation.
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? Answer: The valve will remain closed.
What is the purpose of a flame-proving device in a system with a standing pilot? Answer: It shuts off
the gas flow in case the pilot goes out.
, What safety function does the limit switch perform? Answer: It prevents the furnace from
overheating.
What type of flame proving do direct spark ignition controls use? Answer: Flame rectification.
How does the flame rod sense the flames in a flame rectification circuit? Answer: The flame changes
the AC voltage to pulsed DC current.
The burner assembly and furnace cabinet should be grounded for safety and because? Answer:
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? Answer: Flame
rectification is much faster than anything that relies on heat.
The flame rod in DSI furnaces is? Answer: A steel rod with a ceramic insulator.
What is a gas pilot light? Answer: A small flame that is used to light the main burners.
What is an intermittent pilot ignition system? Answer: The gas pilot is ignited with each call for heat
and shut off at the end of the call.
Gas valves for an intermittent pilot system? Answer: Have both a pilot valve and a main valve.
The operating sequence to light the main burners on an intermittent pilot system is? Answer: The
pilot valve and spark igniter are energized, the pilot flame is proved, and then the main gas valve is
energized.
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