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137 Cards in this Set
- Front
- Back
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What precautions are required when mounting any gas furnace on a wood platform in an attic:
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NONE |
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The gas control valve may be damaged if exposed to an inlet pressure above.
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14 in W.C. |
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How many elbows and joints should a vent connector have:
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As few as possible. |
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The technician is installing a vent system for a condensing gas furnace. The furnace is several feet from a gas water heater. What conditions, if any may the technician route the exhaust of the furnace into the exhaust vent of the water heater:
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Never |
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How may a technician terminate the intake and exhaust for proper operation of a high efficiency gas furnace when using scheduled 40 PVC pipe:
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By using the specific manufacturers termination kit or make one to meet their requirements.
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When suspended with metal strap and no saddle, flexible duct should be:
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1 1/2" |
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A technician is installing a gas furnace and the customer has decided not to install an air conditioner. Making this decision, the affect it will have on the installation of the supply ductwork is:
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Leave adequate space should be allowed for addition of a coil in the future when feasible.
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Leveling of a Mercury bulb is:
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Critical |
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Spray-type atomizing humidifiers are installed to:
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Discharge moisture into the supply duct.
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Electronic air cleaners (EAC) installed in a gas furnace system should be wired so they:
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Only operate any time the EAC On-Off switch is turned to ON.
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The LP gas manifold pressure is commonly:
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10 to 11 in. W.C.
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The polarity of a 120V gas furnace equipped with electronic flame rectification is important because:
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The ignition control may not prove flame.
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Using a voltmeter, a technician can determine voltage drop at a gas furnace:
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With the furnace not operating and then with the furnace operating.
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The setting on a 4 speed PSC blower motor can be changed by changing the:
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Motor Tap Connection |
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When starting up a dual system, the temperature rise method for determining airflow cannot be used with compressor cycle of the heat pump because:
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The capacity of the system varies too much with outdoor temperature.
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The flame pattern a technician would expect to see on a properly operating single stage gas furnace equipped with “in shot” type burner is a:
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Hard and forceful flame with a light blue appearance and little or no yellow.
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Compressed air is recommended for a:
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Pressurization leak test of fuel gas pipe.
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Diaphragm type differential pressure gauge is used to:
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Measure air pressure
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The pressure reading on a manometer is expressed in:
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Inches of water
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A technician measures the return air temperature of a 100,000 BTU output gas furnace to be 65°F and the supply side air temperature is 135°F:
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The CFM would be 1323.
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A dirty or clogged air filter in an operating gas furnace can cause an:
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Increase temperature rise.
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Bent vanes on a direct drive blower wheel in a gas furnace can cause a:
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Loss in airflow, excessive blower motor wear, and increase noise.
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A gas clothes dryer can interfere with the operation of a nearby natural draft gas furnace with an atmospheric burner by:
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Stealing combustion air preventing complete fuel burning.
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During a preventive maintenance check of a gas furnace:
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Ductwork should always be checked for leaks and damage.
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When performing a cycle check during a preventive maintenance call, the technician should:
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First check with the owner of the equipment for their opinion of performance.~The next step is to turn the unit off at the thermostat system switch. ~Next the technician should set the FAN switch to ON and check that the blower is running.
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The measurements required to calculate the CFM of a gas furnace are:
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Entering air temperature~Leaving air temperature~Outdoor ambient and rated capacity.
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The reason for checking the temperature rise across the heat exchanger of a gas furnace is to:
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Compare temperature differential to nameplate rating.
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The technician is checking the operation of an induced draft furnace with an atmospheric burner and a direct ignition system. On a call for heat the:
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Vent blower comes on~Igniter glows~Main burner does not light~The next check would be the gas supply and/or gas valve
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The technician is servicing a gas furnace located in a basement and the complaint is “not enough heat”. The following conditions exist:
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Properly sized furnace is operating correctlyTemperature rise is within specificationFilter is clean and CFM from blower is properThe most likely problem with this system is the air side is leaking at one or more supply ducts.
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The complaint is that there is static electricity throughout the house. The home has a bypass humidifier. The technician has checked the humidistat and verified that it is set properly.
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The next check would be to see if the humidifier damper is open.
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A customer complains the unit is “blowing cold air”. The technician determines that the problem occurs at the end of the heating sequence. The furnace used an electronic integrated blower control.
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The likely problem with the system is the blower off delay is set too long.
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Undersized ductwork often causes:
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High sound levels~Insufficient air quantities~High static pressures.
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For accuracy, the preferred locations for the temperature probes when measuring temperature rise across a heat exchanger in a gas furnace is to:
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~Read inlet temperature in the return plenum as close as possible to the heat exchanger.~Read outlet temperature in supply plenum as close as possible, but beyond “line of sight” to the heat exchanger.
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A system airflow check determines that supply static is 0.15 in. W.C. and return static is a negative 0.55 in. W.C. these readings tell the technician:
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The difference between supply static and return static is unacceptably low.
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The following measurements would be needed to properly evaluate a complaint of “drafty” operation with a gas heating system:
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System TD,Drop and static pressure
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A furnace is inoperative because of a failure in the ignition sequence at the flame proving stage. To check the flame proving circuit the technician would:
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Connect a microampmeter set to DC microamps in the sensor circuit and operate the furnace.
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A technician receives a call that a gas furnace is running constantly in heating and cannot be shut off. While checking the thermostat, the technician observes the burner shuts off by removing the wire on the R terminal on the thermostat subbase.
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Most likely there is a short in the thermostat subbase.
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The continuity of a fuse should be tested by:
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Checking resistance with power off.
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A standing pilot furnace uses a relay for controlling the supply blower. On a call for heat, the burner lights, the fan control closes, but the blower does not run. A check of voltage at the blower relay coil shows 24V. The load side measures 0V. The technician should replace what:
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Fan relay.
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The following is true about fan run capacitors:
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The fan capacitor shifts the electrical phase angle.
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The pressure switch on an induced draft blower system is not closing properly; the technician can check the pressure using a:
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Bourdon tube pressure gauge.
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The blower access door is removed from a powered up gas furnace with a door interlock switch. Assume the switch has not been modified, the technician read across the door interlock switch terminals should get:
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Volts
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A damaged section of double wall vent pipe is to be replaced with a section produced by a different manufacturer:
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The installer should check the new section for compatible locking joints.
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If too much primary air is used the flame will:
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Lift off the burner.
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What is the problem when a flame on a high efficiency gas furnace is burning primarily yellow:
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The flame is burning without sufficient combustion air.
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The cause of a voltage reading across a closed contact in a 24V control circuit is:
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Pitted or dirty contacts.
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The following are the first two checks typically made on an electronic control:
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Presence of any on board transformer voltage.Proper output voltage.
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During a service call on a unit the technician finds that the wiring diagram is missing from the access panel. The technician may begin troubleshooting by:
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Tracing the circuits either mentally or on a sketch pad.
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The first check made for most electrical troubleshooting is a:
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Voltage check of the supply line.
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The test to be used to check the wiring and connections to the terminals of an energized blower motor is a:
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Voltage test.
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The following conditions exist in a circuit that supplies power to three parallel loads.
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The total current in the circuit when operating will be the sum of the currents through each load.
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To test the continuity of an internal overload protector in a single-phase motor the motor:
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Must be cool.
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A control string is defined as two or more switch contacts connected in a circuit, or set of circuits, to control a load. In order to troubleshoot a load controlled by a control string, the technician must first:
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Check for proper voltage applied across the load.
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When troubleshooting a blower motor circuit on a packaged system, 244V is measured across the motor and no amperage is measured:
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The likely problem with this system is an internal overload device is open.
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The continuity through a de-energized relay coil is checked by using an:
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Ohmmeter
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The industry accepted method for locating a suspected natural gas leak is:
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A soap solution.
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A customer has concerns about carbon monoxide (CO) in their hone. Many of their reported symptoms indicate there may indeed be a CO problem but on each trip the technician makes to check their home the technician finds normal CO levels.
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CO detector reader/recorder would be appropriate to use for determining if a problem truly exists.
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Prior to performing an air balancing check of a newly installed duct system:
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Dampers should be open completely in all rooms.
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An external static check with a high reading indicates that the blower is developing enough:
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RPM
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The following readings, are most appropriate for complete air balancing report
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Total pressureStatic pressureOutlet pressure
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Operating sound a consideration in the location of a heating unit because:
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Excessive noise could be disruptive to the customer.
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A Worn pulley is a cause for:
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Blower belt noise.
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A wet bulb reading that is very close to the dry bulb reading from the same instrument indicates:
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Relative humidity is very high
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You are responding to a report of “drafty air” in a room during the heating season.
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The problem is register velocity is too low.
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Heat always moves to equalize temperature. Convection moves warmer air to the ceiling as it is added to the space which causes:
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The temperature in the rooms not to be the same.
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The secondary condensate drain of an air conditioning coil mounted with a horizontal gas furnace in the attic must always be connected:
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To a location readily visible and according to local code.
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A typical four-way multipositional gas furnace is converted from upflow to down flow by:
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Turning the furnace upside down with specified alterations.
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The role oxygen plays in the proper combustion of natural gas is it:
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Combines with the carbon to form carbon dioxide and with the hydrogen to form water vapor.
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Heat exchangers are typically sealed:
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In the furnace housing by gaskets.
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the most important consideration when working on a gas furnace with ribbon type burners is the:
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Individual burners must be mounted in correct alignment.
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An 80% efficiency gas furnace, mounted in a crawlspace:
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Draws its combustion air from the space surrounding the furnace.
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Combustion air is often brought into a non-direct vent gas furnace, located in an interior closet (confined space).
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Two permanent openings of sufficient size must be used is important to remember.
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A”cross break” made on all sides of any rectangular section of metal duct will:
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Increase rigidity and reduced vibration.
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The voltage most often used to power a residential package unit is:
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240V single Φ.
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When thermocouple pilot flame is lost on a standing pilot gas furnace, the primary component which shuts off gas flow to the main burner is the:
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Pilot solenoid.
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How much of the end of the thermocouple should be enveloped by the pilot flame:
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3/8 to 1/2 inch
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Primary air is mixed with the gas within the:
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Burner head.
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What is the purpose of an induced draft blower in a non-condensing gas furnace:
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To create a negative pressure in the heat exchanger.
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In the sequence of operation of an induced draft, intermittent pilot gas furnace:
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The induced draft motor starts when the thermostat calls for heat.
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A gas furnace with a standing pilot uses a flame switch for proving pilot flame.
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Several millivolts are generated by the flame.
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The purpose of a secondary heat exchanger in a condensing gas furnace is to:
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Extract additional heat from the exhaust gas.
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An intermittent pilot gas furnace is one in which:
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A pilot is lit on every call for heat
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The height limitation for a vertical combustion air intake on a condensing gas furnace is:
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Set by the furnace manufacturer.
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The relationship between inrush current and holding current of a relay coil is:
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Inrush current is always greater than holding current.
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On a single stage combination gas valve with a thermocouple flame proving circuit:
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The main burner gas flow is in series with the pilot gas valve.
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A thermopile system usually generates its own control circuit voltage of:
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750 mV.
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Seven Day programmable thermostats are designed to be individually programmed:
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For each day of the week.
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The range of temperature over which an electromechanical thermostat does not call for heating or cooling cycles when set in the AUTO mode is called the “deadband” of the thermostat:
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The Deadband prevents a system changeover within 1° F of any setpoint.
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For indoor air quality purpose, economizers or fresh air supplies should:
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Never be located near a sewage vent.
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Roll out switch is considered a:
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Fire protection device on a gas furnace.
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There are two generally used methods for controlling temperature and humidity within individual zones of a residence.
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One is to use dampers to control supply airflow to each zone.The other is to use separate and independent systems to condition the air in each zone.
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A packaged unit in a two story installation is to be located at ground level with ductwork running up the outside wall to a chase in the second floor.
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The precautions need to be taken with outside ductwork is it must be insulated and weatherproofed.
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The maximum flue gas temperature for condensing furnaces utilizing schedule 40 PVC pipe is:
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140 degrees F |
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The maximum recommended face velocity for a residential non-filter return grille is:
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800 fpm |
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According to mechanical codes, the unobstructed working space should be provided along the entire front (or firebox side) of a warm-air gas furnace installed in an attic is:
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Not less than 30” in depthandNot less than 30” in height.
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The initials “AFUE” represent:
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Annual Fuel Utilization Efficiency. |
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The INPUTS to a typical integrated control board in a high efficiency furnace are the:
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Thermostat voltage from WFlame proving signal& pressure switch voltage.
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On a 20 amp (FLA) motor the minimum circuit ampacity (MCA) should be:
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25 amps
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Differential pressure gauge (also called a manometer) is used to:
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Measure duct static pressure.
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A line voltage fuse is sized to protect from:
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Excessive voltage
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Forced air residential / light commercial gas furnaces provide heat by
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Circulating air across the heat exchanger
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No mechanical fasteners should be used to install
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Floor diffusers in boots or register boxes
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A gas furnace should reach a steady state
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Before taking a combustion test
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The primary purpose of an off delay timer for a gas furnace is t
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Control the indoor blower OFF delay at the end of a thermostat call for heating
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The maximum acceptable supply voltage tolerance for a 120 V circuit is
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+/- 10%
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With a non-direct vented furnace located in a basement, the requirements for the space to qualify as an ‘unconfined space’ is
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At least 20 cubic feet of air volume for every 1000 Btu/h capacity of combustion appliances in the space
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There is little difference between electromechanical thermostats and electronic programmable thermostats
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They are designed to be interchangeable
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According to the International Fuel GAS CODE, the minimum vertical separation for a flue vent termination located above and within 10’ of any forced air inlet to a building is
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6' |
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3/8 to ½ inch of the end of the thermocouple
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Should be enveloped by the pilot flame
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Motor horsepower is one of the criteria used when:
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Selecting a replacement indoor blower motor.
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The typical material used to construct a heat exchanger in an 80% efficient gas furnace is:
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Galvanized steel.
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Electronic air cleaners for gas furnaces are sized based on the:
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CFM of the return side of the heating system.
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A system that is oversized for the load:
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Will cause the unit to short cycle.
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Drive cleats are typically installed:
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On the short sides of a rectangular duct.
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Air leakage into a conditioned space is:
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Infiltration
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An important consideration when installing a motorized economizer is to:
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Check to be certain that the vanes operate without binding.
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A technician wishes to determine the air flow of a gas furnace on startup using the temperature rise method, the following conditions exist:
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The gas meter has been clocked and the flow rate has been determined~The gas heating value is known~The heat rise across the heat exchanger is measured~Next he needs to calculate the CFM using a formula.
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Induced draft blowers in direct vent condensing furnaces pull:
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Outside combustion air only.
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A meter reading microfarads is used to:
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Check a run capacitor with a capacitance tester.
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The setting that brings on the medium high blower speed should be:
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Set on the thermostat when performing an air balancing check of a cooling system.
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Before starting a gas furnace after installation, the technician should do a:
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Visual check of all wiring and that all connections are secure and tight.
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The vent height for a Category I vented appliance referred to in venting tables is the:
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Height from the furnace flue collar to the top of the vent.
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In order to ensure proper combustion air is available in a crawlspace application of a direct vent gas furnace there must be an:
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Air intake connected from the outside to the furnace combustion air opening.
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A vertical vent in an induced draft non-condensing gas furnace that is oversized for its furnace capacity will have:
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Inadequate pressure in the vent.
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Inadequate system airflow will cause a:
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Temperature differential across the heat exchanger that exceeds the manufacturers rating plate.
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Leak detecting solutions specially formulated for use on gas piping are:
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Preferred over household soap because house solutions are more expensive.
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The typical load rating of the branch circuit over-current protection for a residential gas furnace is:
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25 amps |
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A transformer with a 24V secondary repeatedly fails. The technician determines the load in the secondary circuit to be
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2 amps |
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The smallest acceptable transformer used as a replacement is a:
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60 va |
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The outdoor winter temperature for a gas furnace is called the:
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Outdoor design temperature.
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The tables for winter outdoor design temperature are measured in:
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Dry bulb temperature only
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When a gas furnace is installed with an air conditioning coil:
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The coil is installed so that air passes across the furnace heat exchanger first.
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Some steel heat exchangers are coated to prevent:
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Rusting of the heat exchanger
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To minimize noise problems in residential duct systems, the range (recommended to maximum) of air velocity in the rectangular main supply trunk is:
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700 to 900 fpm
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The acceptable source of combustion air for a non-direct vent condensing gas furnace is:
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Any interior unconfined space.
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When performing planned maintenance on a gas furnace check the wiring to be certain that:
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No wires have been broken or become loose.
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A technician should consult WHAT to make an accurate residential load calculation.
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Manual J is the ACCA manual.
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