Heating

Question 1

What is the recommended gap for ignition spark?

Answer 1

1/8”

Question 2

Which pilot system needs to be dealt with carefully because it may damage some electrical meters when taking the flame current?

Answer 2

The single rod system

Question 3

What builds up on HSI and flame rods and impedes the current flow for flame proving. Can it be fixed?

Answer 3

Develops and oxide coating. Flame sensor can be cleaned but replacement recommended for HSI

Question 4

What are HSI made out of and which is more brittle

Answer 4

silicon carbide and silicon nitride. Carbide is more brittle

Question 5

How many volts is connected to the hot surface igniter?

Answer 5

115 VAC

Question 6

Can an HSI be used as a flame sensor?

Answer 6

Yes

Question 7

What should you use to clean a flame sensor?

Answer 7

Scotch Brite pads or 000 Steel wool

Question 8

What are the two ways you can prove flame? Which is the most reliable and why

Answer 8

Flame conductivity and flame rectification. Flame conductivity is not used because it can’t distinguish between flame and short circuit (two rods)

Question 9

What is the difference between a single rod and two rod ignition system

Answer 9

Single rod has one rod to do both ignition and flame sense. Two rod has one for each function.

Question 10

What is flame ionization?

Answer 10

Heat from the flame causes the molecules between the electrodes to collide forcefully and it knocks some electrons out of the atoms, producing ions. Positive ions are attracted to the negative electrode while negative ones are attracted to the positive electrode.

Question 11

Explain Flame Rectification for a short answer question on the test

Answer 11

A flame and flame rod/ground become a device that converts alternating current into direct current. The flame sensor is energized with 100 VAC, flame ionization occurs in the flame and a 4-6 micro amp DC signal returns to the module to verify flame via ground. For best operation the area of the ground electrode must be at least 4 times that of the flame rod. (10x is optimal)

Question 12

In Flame rectification which of the electrodes is larger?

Answer 12

The ground electrode (burner ground) is much larger than the flame rod. Minimum of 4:1 ground to flame rod. Optimal is 10:1

Question 13

In flame conductivity systems which electrode is larger?

Answer 13

There are two electrodes, flame rod and ground and they have similar or equal surface area.

Question 14

When the flame rod is positive: Current flows
When the flame rod is negative: Current flows
What kind of signal results from this?

Answer 14

More current flows
Less current flows

Effectively results in a pulsating DC current that is required to pull in the flame relay

Question 15

True or False:

The larger the ratio of ground area to flame rod area, the greater the flow of current in the proper direction

Answer 15

True: larger ratio results in greater flow of a rectified current

Question 16

In a flame rectification system, what happens if a short circuit occurs?

Answer 16

The module received an AC signal and the system will shut down.

Question 17

How do you solve the problem with flame proving if the micro amp signal being received is not strong enough to prove flame?

Answer 17

You can adjust the areas of the electrodes immersed in the flame until the signal is strong enough to prove the flame

Question 18

What is a Safe-Start check?

Answer 18

Ignition module checks to ensure there is no false flame signal, if a flame is detected it shuts everything down and goes into lockout

Question 19

What is a post purge cycle?

Answer 19

On some furnaces the inducer fan continues to run after the burners are shut down.

Question 20

What else starts when the ignition cycle starts?

Answer 20

A lockout timer. If the pilot isn’t proven in the allotted time the module shuts off gas and spark.

Question 21

What is a recycling control? What kind of appliances are not allowed to have these l?

Answer 21

If a furnace tries to restart even once it’s considered a recycling control.

Continuous trial is not allowed for propane appliances or direct ignition systems.

Question 22

How long is the blower off delay setting in a furnace?

Answer 22

90-180 seconds most common
Furnace blower off delay is adjustable from 90-240 second delays

Question 23

What two factors do you check when calibrating thermostats?

Answer 23

Operating temperature and operating differential

Question 24

What is the operating differential of a thermostat?

Answer 24

It is the range of temperature required to make the thermostat open or close

Question 25

What is a common cause of a gas valve failing to close?

Answer 25

A short circuit

Question 26

What is the minimum gas pressure needed for a gas valve to operate properly

Answer 26

2” wc to overcome the weight of the diaphragm and spring tension

Question 27

How do you determine a faulty electromagnet?

Answer 27

A continuity test High ambient temps weaken electromagnets over time as well

Question 28

What is the difference between a redundant gas valve and a combination gas valve?

Answer 28

Combination incorporates three major components: solenoid valve, diaphragm valve and a pressure regulator. Redundant valve incorporates two components: diaphragm valve and solenoid valve

Question 29

What is the main difference between an intermittent pilot gas valve and a direct ignition gas valve?

Answer 29

The direct ignition gas valve has no pilot connection

Question 30

When using electronic ignition, what is the process of proving the flame called?

Answer 30

Flame rectification

Question 31

What is the minimum flame rod to ground electrode area that is immersed in the flame?

Answer 31

1:4

Question 32

What is the cause of yellow tipped flames?

Answer 32

Not enough airflow Yellow flames indicate incomplete combustion

Question 33

What causes flame lift?

Answer 33

Velocity too high

Question 34

What causes a waving blue flame?

Answer 34

Drafts/ air blowing on burner, cracked heat exchanger

Question 35

What causes flashback?

Answer 35

Not enough gas pressure

Question 36

What is the cause of the main burner flame being too large?

Answer 36

Too much gas

Question 37

What is the cause of noisy flame?

Answer 37

Too high velocity

Question 38

CO ppm of 50 has what effect?

Answer 38

.0005 % CO is the concentration allowable for 8 hour exposure

Question 39

CO ppm of 4000+ has what effect?

Answer 39

0.40 % and above are concentrations which are fatal with exposure less than 1 hour

Question 40

Yellow flames indicate what?

Answer 40

Incomplete combustion, which causes Aldehydes and CO

Question 43

After a safe start check, the ignition sequence initiates and has an ignition timer, how long is it?

Answer 43

17-34 seconds

Question 44

How hot does a hot surface ignitor get? How many volts goes to this?

Answer 44

2600°F 115 VAC

Question 45

What is the difference between a pictorial and a schematic diagram?

Answer 45

Pictorial = connection and has wiring connections and wire colours * drawn as if the appliance is in standby (no call for heat) Schematic = ladder and is helpful in determining the sequence of operations for troubleshooting *drawn with the appliance in standby (no call for heat)

Question 46

What is the recommended first step when assessing a wiring diagram?

Answer 46

Locate the transformer

Question 47

What is the proper velocity range for a direct fired burner?

Answer 47

2500-3200fpm

Question 48

Most direct fired MUA units have a supply air temp of ________________?

Answer 48

50F-100F

Question 49

What is an isolation gas clock for a make up air unit?

Answer 49

A manual valve used to isolate the supply of gas to the entire unit and burner train. Located outside the unit.

Question 50

What is a pilot needle valve on a make up air unit?

Answer 50

A manual valve with fine adjustment, controls the flow of gas and the flame characteristics of the pilot burner. It is located inside the control compartment.

Question 51

What is a safety shut-off valve on a make up air unit?

Answer 51

Automated 2 position valve used to automatically control the flow of gas both on and off to the main burner. It is located inside the control compartment of the unit.

Question 52

What are some common negative pressure problems associated with a make up air system?

Answer 52

- Exhuast fan losing performance. - Exterior doors becoming difficult to open. - Drafts occuring around exterior windows, doors, other openings. - Infiltration of outdoor air through the building envelope. - Reverse flow on smaller exhaust fans. - Poor indoor air quality.

Question 53

What is direct compensating ventilation?

Answer 53

When conditioned air is delivered to the immediate area of the exhuast.

Question 54

What is general area ventilation?

Answer 54

When conditioned air is delivered to the entire area of a building, exhaust fans are used to create spaces of negative pressure to direct the flow of air through the building.

Question 55

When refering to space pressure control systems of make-up air units, when is a constant air supply (constant air in with variable exhaust out) recommended?

Answer 55

When a hot or contaminated environment must be ventilated while maintaining positive room pressure.

Question 56

When refering to space pressure control systems of make-up air units, when is a variable air supply (variable air in with constant exhaust out) recommended?

Answer 56

When fume hoods are used to provide critical ventiliation of heat or contaminants from a clean area while make-up air is used to maintain positive pressure to prevent infiltration.

Question 57

What type of dampers are preferrable for use on the outside of a MUA unit?

Answer 57

Parallel blade isolation dampers.

Question 58

Where do the high and low velocity airflow switches read across in a direct fired make up air?

Answer 58

Across the profile plate.

Question 59

What is the maximum amount of return air that can be used for recirculation on a direct fired make-up air according to ANSI standards?

Answer 59

80% return - 20% fresh