Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

1070 > Final > Flashcards

Final Flashcards

1
Q

Flame rectification is a process by which:

A

An electrical current passes through a flame

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What commonly causes the problem of having to relight the pilot and condensation on windows?

A

A cracked heat exchanger

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How would you correct the short cycling problem in a furnace without a heat anticipator?

A

Adjust the thermostat cycle rate per the furnace manufacturer’s instructions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What instrument do we use to measure gas pressure with?

A

Manometer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Name 3 types of igniters used in gas furnaces.

A

Spark igniter, hot surface igniter, intermittent pilot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What could cause a furnace to stay on too long and create cold drafts?

A

No humidifier installed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

True or False? When venting a Category I furnace, best results can be obtained if Type B, double wall pipe is used for the vent and vent connector.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What precaution must be taken during the installation of Category IV (condensing) furnaces?

A

Make sure the vent pipe slopes back toward the furnace

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What must be done if manifold pressure cannot be adjusted to fire the burners at the correct input?

A

Replace orifices with ones a size larger or smaller

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What should you do if the pilot flame is yellow and soot has accumulated around the pilot assembly?

A

Disassemble and clean the pilot assembly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the first major event in the ignition sequence of an induced combustion furnace?

A

The energizing of the spark ignition module

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

True or False? For correct natural gas system operation, burner manifold pressure must be set at 3.5 inches w.c.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Which troubleshooting step for spark re-ignition is incorrect?

A

Check for spark with screwdriver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Can a glow coil remain energized continuously without risk of burning out?

A

False

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Most glow coils require an adjustable resistor in series to:

A

Increase glow coil temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Put these steps in the proper sequence for direct burner ignition:

A

Purge combustion chamber with inducer fan for 15 seconds
Energize hot surface igniter for 17 seconds
Energize gas valve for 5 seconds
Check flame sensor for next 2 seconds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

In an atmospheric gas burner, the presence of a yellow or orange flame indicates:

A

Not enough primary air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does the equation [CFM = Btuh / (1.08 × Temp rise)] determine?

A

System airflow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Where is manifold pressure on a gas furnace measured?

A

Between the gas valve outlet and the orifice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the most likely problem if the pilot is lit but the main gas valve will not open?

A

The limit switch contacts are closed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What would a heat anticipator set to ‘longer’ most likely cause?

A

Short blower ‘on’ cycles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

One cubic foot of LP gas (propane) contains _____ BTU’s of heat energy than one cubic foot of natural gas.

A

More

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Where is the secondary or auxiliary limit switch located?

A

In the blower compartment of a downflow furnace

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Almost all burner problems are caused by improper ___________.

A

Primary air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What causes yellow-tipping?
Shortage of primary air
26
How do you correct lifting flames?
Decrease primary air
27
What occurs when burning speed is greater than the port velocity?
Flashback occurs
28
What may wavering flames indicate?
Varying gas pressure
29
What results if the burners do not light as soon as the gas valve opens?
Delayed ignition
30
How can flame rollout usually be corrected?
By making sure the front panel is sealed
31
What occurs when the room temperature drops below the setpoint?
A demand for heat occurs
32
Which factor has the least effect on thermostat performance?
Exposure to air flow from the supply registers
33
What is the purpose of the heat anticipator in a thermostat?
To provide all the heat necessary to satisfy the thermostat
34
What condition would cause the high limit control to open the circuit on a central gas furnace?
The fan control is open
35
What could cause a situation where the flame continually rolls out the front of the heat exchanger?
A heat exchanger or vent that is plugged
36
What is the problem if an intermittent spark ignition system does not receive a flame recognition signal?
No flame recognition signal is received
37
What happens if the heat anticipator in a thermostat fails to open?
Failure of the heat to turn off
38
What must be provided for proper furnace vent operation?
Adequate combustion air
39
What type of gas application can a spark ignition system with a continuous trial for pilot ignition be used on?
Natural or LP gas application
40
What is air that is pre-mixed with the gas in the burner called?
Primary air
41
What is the most common cause for the limit switch to open on a residential gas furnace?
The blower speed is too low
42
What does a voltage reading of 24 volts across a gas valve solenoid indicate?
The gas valve solenoid coil is good
43
True or False? A thermopile thermostat should never be connected to any source of power other than a millivolt pilot generator.
True
44
Hot air will hold _____ moisture than cold air.
More
45
What should a technician do if the manifold pressure is 3.5” WC and the temperature rise is outside the rating plate's specifications?
Increase the blower speed
46
What is the approximate manifold pressure for proper LP gas fired furnace operation?
11 inches of water column
47
In the cooling cycle, how is the operation of the indoor blower controlled?
By the blower relay
48
What could cause a short burner 'on' cycle followed by a shutdown?
A limit switch opening due to overheating
49
When does the fan control in a gas furnace energize the blower motor?
When the furnace heat exchanger reaches a preset temperature
50
What must be done during venting of high-efficiency furnaces to prevent contamination from entering the gas valve?
Prevent condensate from entering the gas valve
51
When does the fan relay or fan control turn off the indoor blower in a heating cycle?
When the heat exchanger cools below the fan-off temperature
52
What happens if the limit switch opens during furnace operation?
The gas valve closes and shuts off the burners
53
What is the purpose of the rollout switch in a gas furnace?
To shut off gas flow if flames roll out of the combustion chamber
54
How is ignition typically proven when a furnace uses a hot surface igniter?
With a flame sensor
55
What does the flame sensor detect?
Microamps of current through the flame
56
Why must vent piping slope back toward the furnace on condensing units?
To allow proper drainage of condensate
57
What will happen if the inducer motor does not run at the start of the heating cycle?
The pressure switch will not close and the ignition cycle will not proceed
58
What is the function of the pressure switch in an induced draft furnace?
It proves that the inducer is running and the vent is clear
59
What should be checked if the furnace starts but the burners shut off after a few seconds?
Flame sensor cleanliness and signal strength
60
What two functions does a fan-limit control switch perform?
It turns the blower on/off and shuts off the burner if the furnace overheats
61
How many inches of water column does a typical natural gas system operate at?
3.5 inches
62
What can cause lifting flames in a natural gas furnace?
A reduction in primary air
63
What could cause a gas furnace to be turned off by the high limit?
A burned out transformer
64
What is true of a gas furnace with a non-100% shutoff gas valve?
If the pilot flame goes out, pilot gas will still continue to flow
65
What could cause intermittent cycling of burners in a condensing furnace?
Blockage or restriction in the combustion air or vent piping
66
What must be done when replacing a natural draft furnace with a non-condensing, induced combustion furnace?
Line the masonry chimney with an approved liner
67
Which components provide the same function?
Fusible link and flame rollout switch
68
What does the fan switch regulate on a gas furnace?
How fast the inducer will run
69
What type of gas system can a spark ignition system with continuous trial for ignition be used on?
Natural or LP gas application
70
What is air that is premixed with the gas in the burner called?
Primary air
71
How many BTUs of heat energy does one cubic foot of natural gas contain?
Approximately 1000
72
What is a direct drive blower?
One in which the blower is attached to the motor shaft
73
How is temperature rise on a furnace defined?
Temperature of supply air minus temperature of return air
74
What device stops the flow of gas to the burners when the pilot flame is extinguished in a standing pilot gas furnace?
The pilot safety solenoid
75
What is likely the cause if the spark ignites the pilot flame but the main gas valve will not open?
Flame rectification current is low or missing
76
What is probably the cause if the gas flame ignites in the venture of the burner?
Too much primary air
77
What is the voltage to energize the igniter in a gas furnace with a hot surface igniter?
120 volts
78
What precaution must be taken when handling a hot surface igniter?
The device is fragile and must be handled carefully
79
What is a possible consequence of too low a temperature rise in a gas-fired condensing furnace?
Condensation may form in the secondary heat exchanger

1070 (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions