Standard Furnace Components

Question 1

Max temp of a furnace by code

Answer 1

250f°

Question 2

Components of a low efficient furnace

Answer 2

Heat exchangers
Gas valve
Draft hood
Burners
Hi-limit
Combination fan limit control
Pilot assembly
Transformer
Thermostat
Flame rollout switch
Draft spill switch
Motor
Manifold orifices
Capacitors

Question 3

What is the fan on temp range
What is the fan off temp range
What is differential temp

Answer 3

120f°(49c°)-140f°(60C°)
90f°(32C°)-100f°(38C°)
Min 35f° (19c°)

Question 4

How many millvolts are used in a thermocouple

Answer 4

20-30milvolts

Question 5

What changes the rotation of a belt motor

Answer 5

Reverse the wires under the cover plate

Question 6

Type of capacitors
What do they do

Answer 6

Run capacitor
Start capacitor
Hold electricity and starts the furnace process

Question 7

Furance sequence of operation

Answer 7

1. T-stat calls for heat (R and W closes)
2. gas valve opens/energized
3. Pilot light ignites burners
4. Fan control turns on
5. Blower motor energized
6. T stat satisfied
7. R and w opens
8. Gas valve de energized
9. Burners extinguish
10. fan-off temp reached
11. Blower motor de energized
12. Stand by

Question 8

Manifold pressure

Answer 8

3.5” W.C.

Question 9

Configurations of furnaces

Answer 9

Up flow, down flow, horizontal, all positions

Question 10

What switch measures temp once heat exchanger is warmed up

Answer 10

Fan switch or fan control

Question 11

When T-stat is satisfied, what happens

Answer 11

Turns off electrical circuit to gas valve
“De-energized”

Question 12

Furance operation process is called what?

Answer 12

Heating cycle

Question 13

Controls used to operate furance are called. What are they

Answer 13

Operating controls
Thermostat, fan control,transformer,gas valve, and motor

Question 14

Controls to make sure the operation is safe are called?
What are they?

Answer 14

Safety controls
Limit switches and thermocouple/ therompile

Question 15

What is a standing pilot
Variations of pilot

Answer 15

Is a small flame that burns 24/7 located near main burner
Aerated, post-aerated (most common), and non aerated

Question 16

If the pilot is out of alignment, what can happen
What is it called

Answer 16

Gas flows to burner to long and accumulates. When it does ignite causes small explosion.
Delayed ignition

Question 17

What is a thermocoupler

Answer 17

Thermal electric device made of two dissimilar metals (iron and constantan) produces a small voltage 20 to 30 millvolts AC

Question 18

How much should the flame encompass the tip of a thermocouple.

Answer 18

⅜” to ½”

Question 19

What is a thermopile, also known as

Answer 19

Thermocouples wired in a series
Power piles and pilot generators

Question 20

how does a power unit work

Answer 20

If the power unit isn’t getting power from the thermocouple/pile, the electromagnet in it will close the plunger, preventing gas flow.

Question 21

What is the setting on the heat anticipator attached too

Answer 21

Amp draw of low voltage circuit (current draw of control unit to which the Thermostat is installed)

Question 22

What class equipment is a transformer

Answer 22

Type 2

Question 23

What do transformers operate by

Answer 23

Magnetic induction

Question 24

If the secondary has less windings then the primary it will have more or less voltage? What is this Transformer called

Answer 24

Less voltage, a step down Transformer

Question 25

2 types of blower motors

Answer 25

Belt drive, direct drive

Question 26

What do Draft diverters or draft hoods do

Answer 26

Provide a pressure balanced flue. Breaks the stack action while at the same time prevents down drafts.

Question 27

Furnace Rating plates will have what information

Answer 27

Orifices sizes, information on approval agency,altitude rating (listed as sea level) input and out rating of appliance and fuel type

Question 28

3 bimetal temperature sensing devices

Answer 28

Strip, spiral and disc

Question 29

Main purpose of a limit switch

Answer 29

To shut down the gas supply, should the furnace get too hot

Question 30

List the different furnace configurations

Answer 30

Upflow,downflow, horizontal, and all position

Question 31

Why is a Tstat better for controlling the furnace than a light switch

Answer 31

They can monitor the temperature and respond by turning off or on equipment.

Question 32

Once there is a call for heat in a furnace, what happens

Answer 32

Complete an electrical circuit that energizes the gas valve allowing gas to flow.

Question 33

A combination gas valve consists of?

Answer 33

Regulator Manual ON/OFF/pilot valve Control circuit connections Pilot gas adjustment Thermocouple connection Power unit

Question 34

What is CW and CCW stands for what in regards to belt driven motors?

Answer 34

Clockwise and counterclockwise

Question 35

Regardless of hp rating, all belt drive motors rotate at what?

Answer 35

1725 rpm

Question 36

While most belt driven motors are single speed(1725rpm), there are two speed motors. What rpm is the low speed

Answer 36

1140rpm

Question 37

Different between belt and direct motors

Answer 37

Direct drive doesn't have a belt it is mounted directly to the fan unit

Question 38

Direct drive motors have up to how many speeds

Answer 38

5

Question 39

What are most motors in furances called

Answer 39

Squirrel cage induction motors gets name from fan wheel

Question 40

Fans used in furnaces are ____ type fans with____curving blades

Answer 40

Centrifugal, forward

Question 41

If the fan wheel is installed backwards what can happen

Answer 41

Furnace may overheat and be shut off by limit switch

Question 42

Shaft size of a belt driven fan

Answer 42

¾"

Question 43

What happens when adjusting the pulley of a belt drive fan

Answer 43

If the pulley is adjusted in, the diameter becomes larger, and fan speed increases. If the pulley is let out, the diameter will be smaller, resulting in decreased air

Question 44

Direct drive fan shift size

Answer 44

½"

Question 45

What do heat exchangers do

Answer 45

Transfer heat from burners to the air stream.

Question 46

Heat exchangers can be what 3 styles

Answer 46

Clam style, barrel style, or tubural

Question 47

What happens if down draft enter venting system?

Answer 47

Could interfere with the burners or extinguish pilot light

Question 48

What is the venturi effect

Answer 48

the reduction in fluid pressure that results when a moving fluid speeds up as it flows through a constricted section (or choke) of a pipe

Question 49

What happens when manifold pressure is increased or reduced

Answer 49

If increased will cause more air to enter burner resulting in flames lifting off burner If reduced, then air gas mixture is reduced, and flashback will occur

Question 50

The venturi tube is also called? What does it do

Answer 50

The mixing tube Mixes the gas and air for the burner through high speed low pressure

Question 51

Inside the heat exchanger, heat from burners transfer through what process?

Answer 51

The heat from burners transfers through convection and radiation up the metal surface of the

Question 52

What is the job of a burner

Answer 52

Transforming a combustible fuel into heat

Question 53

Two types of burners

Answer 53

Upshot and In-shot

Question 54

Can you just resize the orifice size? What about converting to a different gas

Answer 54

Under no circumstances should you. If furance is to be converted from one gas to another, you can install a factory conversion kit only.

Question 55

Purpose of the flame rollout switch

Answer 55

The flame rollout switch is a safety feature that shuts off the gas supply to the burner if the flame blows out.

Question 56

What common voltage, used in furnaces, is found on the secondary side of a transformer?

Answer 56

24V