1 Flashcards
A good description of how a bi-metal fan switch operates the blower motor on a gas furnace is:
Temperature on - temperature off
A gas furnace is to be installed in a garage. The national standards require that the burners and ignition sources must be located ….. From the floor.
18 inches
Redundant gas valves used on gas furnaces will shut down if gas pressure exceeds?
13.5 in. W.C.
Burning one cubic foot of liquefied petroleum gas completely will produce approximately…. BTUs
2000-2500
LP gas has a specific gravity of:
1.5-2.0
What is the purpose of a spoiler screw located on a burner, or adjustable-shutters?
Mix primary air and gas
Furnace limit switches are wired in series with the:
Gas valve
A tech is using an extension ladder to work on a roof top unit. The top of ladder should extend how much beyond the support joint.
3 feet
A technician determines that a natural gas furnace has a defective heat exchanger. The technician should:
Inform the homeowner, turn the thermostat off, turn the gas to the furnace off.
A natural gas (standing pilot) furnace usually requires….gas pressure at the manifold and burners.
3.5 in. W.C.
The vent system for a condensing furnace is classified as…. by the national field gas code.
Category 4
Type B vent pipe must be kept at least….from combustible materials.
One inch
All condensing furnaces manufactured after 1992 must have a AFUE rating of at least:
90%
You have installed a category 4 two-type vent system that terminates through the roof of the residence. The elbow for the combustion air intake, above the roof, should:
Point down
The reason heating thermostats have anticipators is to?
Reduce overshoot
The typical flue gas temperature of a category 3 furnace is:
280F- 300F
The proper chemical name for natural gas is?
Methane
Burning one cubic foot of natural gas will produce approximately….BTUs.
900-1100
A furnace nameplate specifies a temperature rise of 40 to 70 degrees. Temperature measurements indicate a rise of 80 degrees. The most appropriate action is to:
Increase fan speed
A BTU is the amount of heat required to raise the temperature of one pound water:
One degree Fahrenheit
Natural gas piping must be sized to prevent excessive pressure drops. The national fuel gas code maximum pressure drop allowance is approximately:
.35 in. W.C.
Gas piping must be installed with a pitch of:
1/4” per 15’ run.
Pipe joint compound should be applied to:
Male threads less two end threads
A technician is installing a copper elbow on LP gas line; what type of solder is recommended:
95/5 solder
To burn one cubic foot of Natural Fas completely, at least…. of combustion air must be available.
15 cu ft.
The ignition temperature of Natural Has is?
1000-1200F
Air that is mixed with Natural Gas in the burner is called:
Primary air
A Natural Gas furnace is operating properly. How many cubic feet of flue gas are needed for every one cu. ft. burned?
20 cu. ft
The purpose of a flue baffle is:
Increase heat exchange.
The LP gas pressure supplied to the gas valve should be:
11-13 in. W.C.
An installed gas furnace should have a minimum of….inches for service access.
30 inches
What would cause the temperature limit safety to shut off the burner?
Fan motor failure
The cut off plate is a component of the:
Blower housing.
A “spud” or burner orfice does what?
Meters gas to the burner
A good thermocouple should read approximately …..on a D.C. meter.
18 millivolts
Liquefied petroleum, ( LP) gases are:
Propane and butane
Fan tine/temperature delay switches are used to:
Allow the vent to create proper draft and allow the heat exchanger to warm up
What instrument would a technician use to calculate return airflow to a furnace?
Meg get
A furnace with a hot surface igniter will not light. Before changing the igniter the technician should:
Check voltage to the igniter
A technician starts a standing pilot furnace and notices on main ignition the flames “roll out”. The technician suspects:
A faulty vent
A technician servicing an LP gas furnace notices a tag stating it was converted from natural gas. He finds large amounts of soot in the heat exchanger. What could be the cause of this soot?
Orifice, (spud) too large.
A customer tells a technician that his six mont old furnace stops heating before the residence is warm. This happens only on very cold nights. The technician lights the furnace, and tries to adjust the gas valve, but the flames do not change. He suspects:
A defective gas regulator.
A standing pilot furnace had a bi-metal fan control. What are the factory settings?
Fan on 125F / Fan off 80F / Limit cut out 200F
Type B vent pipe is constructed with an inner pipe and outer pipe. The inner pipe is made of what?
Aluminum
On a dedicated vent system, a fire stop support is located:
Where it passes through a ceiling
When venting Category 1 furnaces, it is sometimes necessary to increase the vent pipe size. The proper location to adapt to the larger vent is:
At the furnace connection
You are installing 1/2” and 3/4” black iron pipe to a natural gas furnace. What is the approximate number of threads to cut?
8-10
The proper name of the tool used to clean the inside of steel pipe is a?
Reamer
Clevis, ring, and single hook are types of :
Hangers to support gas piping
The proper name of the tool used to cut the threads of a steel pipe is a:
Die
You are installing two sections of a rectangular sheet metal duct to the main supply line. What connectors are used to secure sections of the trunk line?
A connectors and drive clips.
Metal ductwork tends to transmit noise and fan vibrations to conditioned spaces in residential installations. What type of connectors are specified to control this?
Flex connectors
Duct wrap is used to insulate round metal ducts. What is the approximate R- value for “one inch” of this insulation?
R=4.0
A category 1 natural gas furnace has a typical air temperature rise of:
40F-70F
A technician connects the electrical circuit to an 80,000 BTU gas furnace with a 3-ton cooling system. The fan motor is rated 1/3 HP @ 120 VAC. What size conductor would normally be used? (Copper conductors)
12-14 AWG
A GFCI circuit breaker detects:
Current leaks to ground
A homeowner complained that his furnace makes a loud bang upon ignition. The technician decides to check the gas pressure and finds 3.2 in. W.C. at the manifold. The technician should:
Check the supply gas pressure
The proper instrument for measuring carbon dioxide is a:
Combustion analyzer
If voltage is applied across two speed terminals on a fan motor, the motor will:
Short out
The maximum static pressure on a typical gas furnace blower system is:
.7 - .9 in. W.C.
Induced draft furnaces have a vent safety switch that should open at?
100F
Thermostat wire comes in two standard gauges:
22 and 20 AWG
A technician solders a spade connector to a wire. What type of solder should he use?
Rosin core
The anticipator is wired in series with the?
Gas valve
To change the speed of a belt driven blower, the technician should:
Adjust motor pulley
How much current does a typical flame sensor produce?
1-30 microamps
A typical vent stack temperature on a category 1 furnace is?
350F-450F
A customer complains that a 2 year old gas furnace will not light. The technician determines that the furnace locks out while attempting to light. He reads 19 VAC at the gas valve and concludes
The transformer could be faulty.
The pilot assembly orifice of a spark ignition furnace is completely clogged. The technician should:
Replace it
Carbon monoxide is dangerous. What percentage of CO is acceptable in a sample of the flue gas?
.04%
A technician starts up a 15 year old natural gas furnace. The main burner lights and after 60 seconds the blower fan comes on, but the blower flames wave in one corner. The technician suspects:
A faulty heat exchanger
A technician starts a spark type ignition furnace. The main burners light, but the spark igniter continues to spark. After 60 seconds, the blower fan comes on and the burner goes out. The technician suspects:
A faulty ignition board
A gas furnace has an induced draft fan. What switch must operate properly before ignition sequence?
Differential air pressure
A technician reads 0 Ohms between the common and low speed wires on a 120 VAC furnace motor. From this the technician determines that the winding is:
Shorted
On his ohmmeter a technician reads infinity between the high and low speed wires on a 120 VAC furnace motor. What does this indicate?
Open
The “bonnet capacity” of a furnace is:
Furnace input BTUs
At what altitude does a gas furnace need to have adjustments made to operated properly?
2000 feet
Failure to wire a replacement low voltage transformer in an electronic ignition furnace, based on it’s noted polarity, will:
Cause flame rectification problems
A spark ignitor operates at?
10,000 VAC and higher
What type of metallic conduit is recommended for indoor use only?
EMT
A furnace nameplate specifies a temperature rise of 40 to 70 degrees. Temperature measurements indicate a rise of 80 degrees. The most appropriate action is to:
Increase fan speed.
A dedicated vent system:
Is the only vent for an appliance.
A yellow flame indicates:
Incomplete combustion is occurring. Soot may be created, which further hampers burner operation. Lack of primary air is the main cause.
A lifting flame indicates:
The gas velocity is faster than the speed at which the gas can burn.
Flashback indicates:
The gas is flowing slower than the speed at which burn is occurring.
A floating flame indicates:
Incomplete combustion is occurring. Soot may be created, which further hampers burner operation. Lack of primary air is the main cause.
Fan speed should be set by:
The temperature rise called for on the data plate.
Gas flow to a natural gas furnace can be checked:
Using the gas meter installed at the site
It the exact amount of air is supplied and perfect combustion occurs, in a natural gas furnace, a specific percentage of CO2 content will be present in the flue gases. What percentage will be present?
11.7% to 12.2%
When an LP unit is properly installed and operating normally, the CO2 content of the exhaust gases:
11% to 12%
While evaluating a gas valve that failed to open, the technician determined that; the gas valve knob in the proper position - the thermostat was calling for heat - the valve is an electric ignition type- continuity of the main gas valve coil was good - and proper voltage was present at the main gas valve coil terminal(s). What action should be taken?
Replace the gas valve
In a house with central return system and seven supplies located in rooms with interior doors, what outcomes are likely when the interior doors ate closed and the air handler is turned on?
The static pressure that the HVAC fan gas to run against is increased resulting in less air through the air handler. The main body of the house experiences negative pressure. The rooms behind the closed interior door become positively pressurized.
The formula (x=sensible heat btu/h/ 1.08 xTD) is used to calculate what?
CFM
The most common burner used in induced draft furnaces is:
inshot
A technician wraps a thermostat wire ten times around his clamp-on ammeter and measures 5.5 amps between R and W terminals on the thermostat sub-base. He should set the heat anticipator to:
.50
A gas valve with 100% shut-mean:
gas to the pilot burner is shut-off
A gas furnace has an electronic control board. How is the fan cycled during heating?
Time
A primary cause of burner “flashback” is:
low manifold pressure
A technician needs to run thermostat wire 75 feet. To avoid a voltage drop the technician should use:
20 AWG
