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90 Cards in this Set
- Front
- Back
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The four types of gas furnace air flow patterns are_________, ________, _________ and___________ |
up flow, down flow, low boy and horizontal
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Describe the function of a multi poise or multipositional furnace.
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Multi poise furnaces can be installed in many positions. Which adds versatility to the furnaces. Multiple safety controls like bimetallic flame rollout or over temperature limits must be designed into the furnace for safety.
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Describe the function of a draft safeguard switch.
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Vent limit or draft safeguard switches are normally close switches usually mounted on the draft hood on near the exhaust vent pipe exit. They monitor the draft hood temperature and open when there is any spillage of flue gas.
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Where are auxiliary limit switches used in heating applications?
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Auxiliary limit switches are usually mounted on the warm air blower housing. Down flow furnaces all have auxiliary limit switches. Which sense room return air temperature and interrupt the burner operation when temperature becomes too high.
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The specific gravity of natural gas is:
A. 0.08. B. 1.00. C. 0.42. D. 0.60. |
D. 0.6
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What is a water and digital manometer?
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A water manometer is a device that cause a rise in a column of water with a rise in gas pressure. A digital manometer measures gas pressure in inches of water column. It has a digital number and letter display and it is very accurate.
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The pressure at the manifold for natural gas is typically:
A. 10 psig. B. 8in. WC. C. 5.5 psia. D. 3.5 in. WC. |
D. 3.5 in. WC.
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What is the approximate oxygen content of air?
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21%
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The typical manifold pressure for propane gas is _________in. WC.
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10.5 to 11.
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Why is excess air supplied to all gas burning appliance burners?
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To ensure that there is enough air at all times.
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The purpose of the gas regulator at a gas burning appliance is to:
A. Increase the pressure to the burner. B. Decrease the pressure to the burner. C. Filter out any water vapor. D. Cause the flame to burn yellow. |
B. Decrease the pressure to the burner.
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True or Falls: All gas valve snap open and close.
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False.
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Which of the following features does an automatic combination gas valve have?
A. Pressure regulator. B. Pilot safety shutoff. C. Redundant shutoff feature. D. All of the above. |
D. All of the above.
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What is the function of the servo pressure regulator in a modern combination gas valve?
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A servo pressure regulator is an outlet or working pressure regulator. It monitors gas s outlet pressure when gas flow rate and inlet pressures vary widely.
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What is a redundant gas valve?
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A redundant gas valve is a gas valve that has two or three valve operators physically in series with one another, but wired in parallel with one another.
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Briefly describe an intermittent pilot gas valve system.
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In an intermittent pilot automatic gas valve system, the pilot will be lit every time there is a call for heat by the thermostat. Once the pilot Is lit and proved, usually by flame rectification, the pilot will light the main burner. Once the call for heat ends, the pilot will be extinguished and will not be relit until the next call for heat. In other words, there is automatic and independent control of the gas flow for both the pilot and main burner.
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Briefly describe a direct burner gas valve system.
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In a direct burner automatic gas valve system, the electronic module or integrated furnace controller lights the main burner directly without a pilot flame. A spark, hot surface igniter, or a glow coil usually accomplishes ignition.
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Where are inshot burners used in heating applications?
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Inshot burners are usually used with induced draft systems, which pull or suck combustion gases through the heat exchanger.
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Describe the difference between a forced draft system and an induced draft system.
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Forced draft systems have a combustion blower motor on the inlet of the heat exchanger. They push or blow combustion gases through the heat exchanger and cause a positive pressure in the heat exchanger. Induced draft system have a combustion blower motor on the outlet of the heat exchanger. They suck or draw combustion gases through heat exchanger an cause a negative pressure in the heat exchanger
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What is an integrated furnace controller (IFC)?
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Many modern gas furnaces use electronic modules or integrated furnace controllers (IFC) to control the operation of the furnace. These controllers often have dual in line pair (DIP) switches that can be switched to re program the furnace to make it more versatile.
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What is meant by the warm air blower's off-delay timing?
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The warm air blower's off-delay timing is used for the fan shutting off once the burners shut off. There are usually four configurations for DIP switches in letting the fan have a 60-100-140or 180- second on-time period after the burners shut off to cool down the heat exchanger. Integrated furnace controllers often have non-adjustable blower fix timing periods for both on and off delays.
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What are dual in-line pair (DIP) switches?
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Many modern gas furnaces use electronic modules or integrated furnace controllers (IFC) to control the operation of the furnace. These controllers often have (DIP) switches that can be switched to re program the furnace to make it more versatile. DIP switches are two positional switches.
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What is a flame rollout safety switch used for in heating applications?
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Flame rollout safety switches protect the furnace from flame rollout. When touched or heated by the flame, the switch opens the circuit to the main gas valve or furnace controller.
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Describe the two types of pilot lights.
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The aerated pilot mixes the air with the gas before burning. The non aerated pilot mixes the air with the gas at the burner outlet.
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True or Falls: A thermocouple develops direct current and voltage.
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TRUE
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Describe how a thermocouple flame proving system functions.
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The operator must hold down a button to allow gas to the pilot burner. When pilot flame is established for a short period of time, the thermocouple will generate enough voltage to hold the pilot light plunger open for continuous flame.
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Describe how a bimetallic flame proving system works.
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Heat from the pilot light wraps a bimetal switch closing the contacts to the main burner solenoid. When the pilot light goes out, switch change to the cold position and shut off the main gas burner.
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Describe how a liquid filled flame proving system works.
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Heat from the pilot light heats a liquid-filled element (mercury) and positions a set of contacts to the hot position which allows power to the main burner gas valve.
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Explain why the preceding flame proving systems called safety devices.
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Because they only allow gas to the main burner when there is a pilot flame to ignite the gas. This helps eliminate escaping gas.
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Describe a flame rectification flame proving system.
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In a flame rectification system, the pilot flame or main flame, can conduct electricity because it contains ionized combustion gases which are made up of positively and negatively charged particles. The flame is located between two electrodes of different sizes. The electrodes are fed with an alternating current from the furnace's electronic module or controller. Current will flow in one direction greater than the other because of the different size electrodes. The flame actually acts as a switch. When the flame is present, the switch is closed and will conduct electricity.
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What is hot surface ignition system.
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Hot surface ignition systems use either 24 V or 115 V to ignite hot surface igniter. This hot surface igniter then either lights the pilot flame or the main burner flame.
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Describe the difference between a single rod (local sensing) and a dual rod (remote sensing) system as they pertain to flame rectification.
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Flame rectification systems can be classified as either single rod (local sensing) or dual rod (remot sensing). Single rod system consist of an igniter and a sensor all in one rod. Dual rod systems use a separate igniter and flame sensor rod.
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Flame current measured in ___________.
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Micro amps
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What is a direct vented furnace?
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A direct vented high efficiency gas furnace has a sealed combustion chamber. This means that the combustion air is brought in from the outside through an air pipe, Which is usually made of PVC plastic.
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What is a non direct vented furnace?
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A non direct vented high-efficiency gas furnace uses indoor air for combustion.
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What is meant by a furnace that has a positive pressure venting system?
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A positive pressure system can be vertically or side wall vented. It is a system whose flue pipe pressure is positive the entire distance to its terminal end.
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Define the dew point temperature as it applies to a condensing furnace.
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The dew point temperature is the temperature at which the condensation process begins in a condensing furnace. The dew point temperature varies depending on the composition of the flue gas and the amount of excess air. As excess air decreases, the dew point temperature increases.
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What is excess air?
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Excess air consists of combustion air and dilution air. Combustion air is primary air and/or secondary air. Primary air enters the burner before combustion takes place. Secondary air happens after combustion and it supports combustion.
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What is dilution air?
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Dilution air is excess air after combustion and usually enters at the end of the heat exchanger.
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What are four factors that determine the efficiency of a furnace?
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Factors that determine the efficiency of a furnace are the type pf draft, the amount of excess air, the temperature difference of the air or water entering versus leaving the heating medium side of the heat exchanger, and the flue stack temperature.
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What is 100% shutoff system?
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A system is 100% shut off when there is a failure in the flame proving device system and both the pilot valve and main gas valve are shutdown.
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What is difference between a hard and a soft lockout?
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Hard lockout is a time period built into the module that allows for certain time to light or relight the pilot or main burner. If this time period is exceeded, the module will go into a hard lockout or shut down. Soft lockout is a time period built in the module that allows for a certain time to light or re-light the pilot or main burner. If this time period is exceeded, the module will go into a semi-shutdown for certain time period, but will eventually keep trying to re-light the system
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What is meant by prepurging a heat exchanger?
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The pre-purge control scheme allows the combustion blower motor to run for a certain time period to clear ( or pre-purge) the heat exchanger of any unwanted flue gases, household fumes, or dust that may have accumulated during the last heating cycle.
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When would a combustion blower ever interpurge a furnace's heat exchanger?
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Inter purge allows for the combustion blower to operate for a certain time period in between ignition tries. Inner purge is usually use when the furnace does not light or does not sense a flame. The heat exchanger must be purged of residual unburned gas or combustion byproducts from the previous unsuccessful ignition attempt.
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What is smart valve system?
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Smart gas valve and an electronic control module in one package.
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An orifice is a drilled hole in a ____________.
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Spud.
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A____________ distributes gas to the various burners.
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Manifold.
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True or Falls: an orifice measures the quantity of gas to the burner as well as direct the gas stream.
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True.
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Name four types of gas burners.
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Cast iron, ribbon, stamped steel, and inshot.
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The _________ transfer heat from the hot gas to the air stream to heat the structure.
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Heat exchanger.
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Name two type of fan switch.
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Temperature-on-temperature-off, and time-on-temperature off.
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When a limit switch circuit opens the circuit to the _____ ______.
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Gas valve
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Describe the function of the draft diverter.
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It induced air from the room while the furnace is operating to cool and dilute the flue gases. Should there be a down draft from the flue, it allows air to spill out into the room rather than impinging on the burner flame.
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describe how a two stage furnace works.
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Modern two stage gas furnaces use a two stage gas valve and a two speed combustion blower motor with two pressure switches to prove the draft. An integrated furnace controller usually controls modern two stage furnaces. Two stage gas furnaces control the temperature in the conditioned space much closer to the set point of the thermostat. Because of this, room temperature swings are smaller and comfort levels are increased.
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describe how a modulating furnace works.
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Modern modulating gas furnaces use a modulating gas valve instead of a staged gas valve. They come with a variable speed warm air blower to vary the speed and amount of warm air. Two stage combustion blower motors are usually standard on modulating gas furnaces. An advanced intelligent integrated furnace controller (IFC) monitors and controls the furnace operations to vary the heating input and warm airflow.
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What is a variable output programmable thermostat?
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Variable output thermostat send a proportional signal instead of an on-off signal to the furnace controller of a modern modulating furnace.
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Why is metal vent often preferred rather than a masonry chimney?
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It gets up to temperature faster, which starts the venting process faster.
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Describe how a vent damper shutoff functions.
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When the burners shut off, the vent damper block the flue gases from going up the chimney to prevent room air from being drawn up the vent during the off cycle.
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Describe why you should never use flame to leak check a gas system.
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Because gas is flammable, and you may create a fire.
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What is the first step a service technician should take when systematically troubleshooting a furnace that contains an IFC?
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One of the first steps in systematically troubleshooting a furnace with an integrated furnace controller (IFC) is to obtain electrical diagram of the furnace and sequence of operation of the IFC.
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A _______ _________ sample is taken from the flue gas to check the efficiency of a gas furnace.
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Flue gas.
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Natural gas is composed of 90 to 95 %
A. Oxygen. B. Ethanol. C. Methane. D. Propane |
C. Methane.
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Liquid petroleum (LP) is composed of liquefied;
A. Natural gas B. Propane or Butane C. Methane D. Sulfur compounds |
B. Propane or Butane
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Natural gas,
A. Is lighter than air B. Has approximately the same specific gravity as air C. Is heavier than air |
A. Is lighter than air.
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Combustion is sometimes expressed as
A. A venture effect. B. Hydro carbonization C. Rapid oxidation D. The mixing of propane and butane |
C. Rapid oxidation.
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A water manometer is used to A : Check combustion B : Measure gas pressure C : Determine the gas burning temperature D : Determine the gas burning color
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B : Measure gas pressure.
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The natural gas flame should be: A : Yellow B : Yellow with some orange tips C : Orange with some yellow tips D : Blue with some orange tips
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D : Blue with some orange tips
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It takes approximately____________ cubic feet of air to produce 2 cubic feet of oxygen to mix with 1 cubic foot of natural gas to produce 1,050 Btu when burned. A : 10 B : 20 C : 30 D : 40
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A : 10
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A standing pilot in a conventional gas furnace: A : Is ignited by an electric spark when the thermostat call for heat B : Is used as a flame proving device C : Burn continuously D : Burned only when the main burner is lit
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C : Burn continuously.
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A thermocouple is used in a conventional gas furnace as a: A : Flame proving device B : Standing pilot C : Limit switch D : Spark igniter
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A : Flame proving device
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The orifice is a precisely size hole in the: A : Manifold B : Spud C : Burner tube D : Combustion chamber |
B : Spud
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The limit switch is a safety device that: A : Shuts the gas off at the pressure regulator when a leak is detected. B : Shuts the gas off if there is a power failure C : Close the gas valve if the furnace over heats D : Close the gas valve if the pilot is blowout
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C : Close the gas valve if furnace is over heats
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In a conventional gas furnace, the hot flue gases are: A : Forced out a PVC vent with a blower B : Recalculated through a second heat exchanger and then vented through the draft diverter C : Forced through the type B vent by blower D : Vented by natural convection
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D : Vented by natural convection.
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A glow coil is used to A : Ignite the main gas burner B : Ignite the pilot when the thermostat call for heat C : Prove the pilot flame D : Reignite a pilot light if it goes out
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D : Reignite the pilot light if it goes out
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A direct spark ignition (DSI) system is designed to: A : Reignite a pilot light if it is blown out B : Ignite the pilot when the thermostat calls for heat C : Provide ignition to the main burner D : Ignite the pilot following a furnace shut down over the summer
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C : Provide ignition to main burner
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A condensing gas furnace uses__________ from a condenser type heat exchanger to improve the furnace efficiency A : Sensible heat B : Latent heat C : superheat D ; Subcooling
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B : Latent heat
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A furnace that can be positioned in more that one position is a: A : Variable furnace B : Multipose furnace C : Flexible furnace D : Diverse furnace
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B : Multipose furnace
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Where are auxiliary limit switches always found in heating applications? A : Up flow furnaces B : Down flow furnaces C : Horizontal furnaces D : None of the above
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B : Down flow furnaces
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Two gas valve physically in series but wired in parallel are A : Series valves B : Redundant valves C : Parallel valves D : None of the above
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B : Redundant valve
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A small microprocessor with integrated circuits mounted on a board to control the logic or sequencer of events of the furnace is: A : Microboard B : An integrated furnace controller (IFC) C : A transducer D : A transformer
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B : An integrated furnace controller
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When a draft blower is located at the outlet of the heat exchanger and causes a negative pressure in the heat exchanger, it is called: A : Induced draft B : Forced draft C : Inlet draft D : Outlet draft
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A : Induced draft
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Flame current in a flame rectification system is measured in ______ unit A : Milli amp B : Milli volt C : Micro volt D : Micro amp
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D : Micro amp
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A furnace that has a sealed combustion chamber and its combustion air comes from outside the conditioned space is a: A : Direct vented furnace B : Sealed furnace C : unitary furnace D : Dual function furnace
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A : Direct vented furnace
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A combination gas valve that has a built-in electronic module in its body is: A : A smart valve B : An intelligent valve C : A control valve D : None of the above
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A : A smart valve
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Another name for remote sensing in a flame rectification system is A : Single rod system B : Dual rod system C : Triple rod system D : None of the above
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B : Dual rod system
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A process where the combustion blower motor runs for a specified time period before the furnace lights to ensure safe ignition is called: A : Post purge B : Power purge C : Pre purge D : None of the above
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C : Pre purge
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Air that mixes with combustion byproducts after combustion at the beginning of the flue pipe is : A : Excess air B : Primary air C : Secondary air D : Dilution air
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D : Dilution air
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A (n)____________ is a furnace's electronic module timed safety shutdown period which may reoccur many times. A : Soft lockout B : Dead band C : Intermission D : Hard lockout
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A : Soft lockout
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When there is a pilot proving device failure and both the pilot and main gas valves are shut down, there is: A : Less than 100% shutoff. B : 100% shutoff C : Intermittent shutoff D : None of the above
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B : 100% shutoff
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An ignition system where the pilot light is only lit during the on-cycle of the furnace is called: A : A direct burner ignition B : A hot surface ignition C : An intermittent pilot ignition D : None of the above
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C : An intermittent pilot ignition.
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