Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

HVAC > Basic Gas Fired, Forced-Air Heating Systems > Flashcards

Basic Gas Fired, Forced-Air Heating Systems Flashcards

1
Q

The electrical energy for operating the ________ in a combination gas valve comes from the thermocouple.

A

power unit

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

Diaphragm valves operate by electrical energy lifting the main valve plunger.

True or False?

A

False

The gas pressure is used to operate the valve.

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

The solenoid is (fast/slow) acting and requires (gas pressure/electrical energy) to operate.

A

The solenoid is FAST acting and requires ELECTRICAL ENERGY to operate.

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

The recommended settings would be for the blower motor to:

Turn ON at _____
Turn OFF at _____

A

Turn ON at 49 to 60 degrees C

Turn OFF at 32 to 38 degrees C

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

How does a open circuit test differ from a closed circuit test

A

Open circuit is preformed while disconnected from the power unit.

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

Explain how a thermocouple operates as a flame proving device

A

The thermocouple provides the energy to hold the power armature coil in. If the pilot light goes out the thermocouple no longer provides energy, so the power unit plunger releases and closes the gas valve

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

In a domestic furnace, the thermocouple should respond to a flame failure within __ minutes, and this is verified by doing a ________ _____ test.

A

In a domestic furnace, the thermocouple should respond to a flame failure within 3 minutes, and this is verified by doing a response time test.

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

Put these events in order, starting with the room getting cold

a) The blower starts
b) The gas valve opens
c) The thermostat contacts close
d) The fan stops
e) The thermostat contacts open

A

c) The thermostat contacts close
b) The gas valve opens
a) The blower starts
e) The thermostat contacts open
d) The fan stops

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

What device may be connected in the 24V circuit or the 120V circuit of a domestic furnace.

A

High Limit

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

What is the recommended setting range for the high limit setting?

______ degrees C to ______ degrees C

A

82 to 93 degrees C

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

Why is it not recommended to use a 120V thermostat in a 24V system?

A

Lack of an anticipator would cause overshooting and would cause too much of a temperature differential.

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

What is the purpose of a step open gas valve?

A

To open the valve partially and allow the main flame to ignite before opening fully, reducing the ignition detonation.

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

Wiring diagrams are the most useful drawing for troubleshooting control circuit problems.

True or False?

A

False; Schematics are usually best

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

In a 24V system, which components may be found in the 120V circuit?

  1. _______
  2. _______
  3. _______
  4. _______
A
  1. High Limit
  2. Fan Control
  3. Fan Motor
  4. Primary Transformer
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

a fan-OFF setting is reached and shuts off; 30 seconds later it restarts even though the burner is off.
This condition is called __________.

A

fan cycling

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

Normal closed circuit voltage of a thermocouple is between 30 and 32 mV.

True or False?

A

False ; The maximum open circuit voltage is between 30 and 32mV.

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

How is the summer switch connected in respect to the fa

A

Series

18
Q

Should solenoid valves be located upstream or downstream of the pilotstat?

A

Downstream

19
Q

What is a HVR?

A

Heat Recovery Ventilator ; an exhaust fan that has a heat exchanger to recover heat from the air being vented outside.

20
Q

Why can’t a relay with a 120V coil connected directly to the exhaust fan circuit be used to switch the Class 2 furnace control circuit?

A

The exhaust fan power circuit wiring and Class 2 wiring are not allowed in the same enclosure.

Using a 120V to 24V transformer will satisfy SEC 16-212

21
Q

A pilot safety switch shuts off gas to the pilot burner.

True or False?

A

False ; It shuts off gas to the main burner, gas to pilot burner still able to flow.

22
Q

120V heating units require a 24V transformer to power the gas valve?

True or False?

A

False

23
Q

When a solenoid gas valve is energized the:

a) plunger is forced away from the magnet
b) plunger is pulled into the electromagnet
c) valve is opened by gas pressure
d) valve will close

A

b) plunger is pulled into the electromagnet

24
Q

A power unit is a electromagnet.

True or False?

A

True

25
Q

The thermocouple produces a voltage by a principal called _______.

A

Thermoelectricity

26
Q

Ignition of pilot burner in a domestic gas fired furnace requires the manual on/off/pilot valve to be in the:

a) ON
b) OFF
c) Pilot
d) More than one

A

c) Pilot

27
Q

The load usually energized by the thermocouple is called the _____ _____.

A

power unit

28
Q

A “closed circuit test” reading off 15mV indicates a faulty thermocouple.

True or False?

A

False

29
Q

“Forced Air Heating” implies that heated air is circulated through the space to be heated.

True or False?

A

True

30
Q

The purpose of the manual switch in a combination “fan control/high limit switch” is to run the fan continuously without relying on the bimetal element to close the fan on contacts.

True or False?

A

True

31
Q

The fan control sensing element in a forced air furnace is located adjacent to the heat exchanger.

True or False?

A

True

32
Q

Step open gas valves reduce the initial rush of gas into the burner.

True or False?

A

True

33
Q

The advantages of using a thermocouple flame proving circuit is its:

a) durability
b) relatively low cost
c) simple construction
d) all of the above

A

d) all of the above

34
Q

All furnaces are designed to blow the heated air out the top of the furnace.

True or False?

A

False

35
Q

Indicate the four steps of a response time test in order:

A
  1. Thermocouple is at a normal operating temperature
  2. Manually turn off gas supply
  3. Start timer
  4. End timer after you hear a click or multimeter jumps
36
Q

In general, the fan-OFF setting in a basic furnace is:

a) approx 24-31 degrees C
b) approx 32-38 degrees C
c) approx 39-45 degrees C
d) Not adjustable

A

b) approx 32-38 degrees C

37
Q

A pilot safety switch is a set of N.O. contacts wired in series with the main gas valve.

True or False?

A

True

38
Q

A heat recovery ventilator is controlled from the R and G terminals of a furnace.

True or False?

A

False; When HRV energized an interlocking system must energize G terminal.

39
Q

Replacing the solenoid valve in a gas heating system requires the new valve to:

a) be installed upstream of the safety gas valve
b) have the same diameter bleed port
c) have the same voltage rating
d) both A and C

A

c) have the same voltage rating

40
Q

A thermostat is usually set in the range of:

a) 10-15 degrees C
b) 15-20 degrees C
c) 20-25 degrees C
d) 25-30 degrees C

A

c) 20-25 degrees C

41
Q

The safety gas valve provides for:

a) shutdown of the main burner only
b) pilot switch operation
c) 100% shutdown
d) safety pressure release

A

c) 100% shutdown

HVAC (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions