Troubleshooting TQ Prep Flashcards
1
Q
Is it considered safe practice to inspect the electrical connections with the power on?
A
False
2
Q
How many voltages does a typical circuit board on any furnace usually contain?
A
Two: 120V and 24V
3
Q
What should you always check regarding blowers?
A
Shipping bolts are removed and that it is secured at the center of the shaft of the motor.
4
Q
What are the three acceptable methods to check for gas leaks?
A
Test dial, commercial leak test, and electronic leak test.
5
Q
In which direction must the venting on the furnace slope?
A
Upwards and away from the furnace.
6
Q
What is the maximum distance supports can be apart on 636 venting?
A
5 feet.
7
Q
What should you always check for on ductwork?
A
Openings that would provide excessive leakage to the system.
8
Q
What should the heat anticipator be set to match?
A
The amperage draw of the 24V circuit.
9
Q
What are the reasons for setting manifold pressure?
A
To confirm it’s not over firing and can be used to derate the appliance.
10
Q
What is the calorific value of natural gas?
A
1000/ft3.
11
Q
What is the calorific value of propane?
A
2500/ft3.
12
Q
What is the formula for converting gas quantity to BTUH?
A
Hourly consumption = Size of test dial divided by the seconds for one full rotation, multiplied by 3600 seconds to get the full hour.
13
Q
What is the formula for BTUH?
A
BTUH = hourly consumption X the calorific value of the gas.
14
Q
How must a metal vent connector be installed?
A
There must be no dips or sags with all the joints fully inserted into each other and locked together.
15
Q
How must the furnace be wired electrically?
A
In accordance with local codes.
16
Q
What must furnaces be derated to at high altitudes?
A
The high altitude rating shown on the nameplate.
17
Q
What is the derating percentage for natural gas and propane furnaces at elevations between 1000 and 4500 feet?
A
4% for each 1000ft above sea level.
18
Q
What are the two types of blower motors?
A
Permanent split capacitor motor (PCM) and Electronically Commutated motor (ECM).
19
Q
What is the most common reason for changing on/off delays in mid or high efficient furnaces?
A
For comfort.
20
Q
What should you do if the temperature rise is too high or low?
A
Change blower speeds accordingly: increase fan speed if too high, decrease if too low.
21
Q
What do two stage gas valves have?
A
Two pressures to set: Hi fire and Lo fire.
22
Q
What will a system with a pilot have?
A
A wire off the gas valve for the standing pilot.
23
Q
What is the main difference between an intermittent pilot gas valve and a direct ignition gas valve?
A
The direct ignition gas valve has no pilot connection.
24
Q
What is the process of proving the flame when using electronic ignition called?
A
Flame rectification.
25
What is the minimum flame rod to ground electrode area immersed in the flame?
1 (Flame rod) : 4 (Ground).
26
Why have flame conductivity systems not been used for proving the flame?
The system will not distinguish between a flame and a short to ground.
27
What is the first step in the sequence of operation for any heating appliance with electronic ignition?
A call from the thermostat.
28
What is the importance of the connection diagram?
It shows where the wires go and the colors of the wires.
29
What is the importance of ladder diagrams?
It shows how appliances work for troubleshooting.
30
What are the two main principles in flame rod detection systems?
Flame rectification and flame conductivity.
31
In a 60Hz system, how many times does it change its direction of polarity?
120 times a second.
32
How is the flame rod mounted?
So it is immersed in the flame.
33
What is HSI made of?
Silicon carbide and is very brittle.
34
What should you never touch with your fingers?
A HSI, as it will burn out at that point.
35
What should you use to clean flame rods?
Scotch Brite pads or 000 steel wool only.
36
What are five parts of a relay?
Coil, core, return spring, armature, contacts.
37
What are the four most common arrangements for the contacts of a relay?
1.SPST-NO (Normally open)
single pull single throw
2. SPST -NC (Normally closed)
3. DPDT - Double pole double
throw
4. SPDT - Single pole double throw
38
What are the two most common capacitors in HVAC systems?
Run capacitor and start capacitor.
39
What is the material used to separate the two plates in a capacitor?
Di-electric.
40
What activates the pressure switch?
The IDM starts turning and creates enough pressure, forcing the diaphragm to move towards the switch, closing it.
41
What is flame rectification?
An AC electrical circuit that sends a very small current from the furnace electronic board up to the flame rod.
42
Where is the CPU located?
The electronic control board contains the CPU.
43
Where is the high pressure switch located in a cooling system?
In the tubing between the discharge side of the compressor and the condensing coil.
44
What is the function of a low pressure switch?
It monitors the refrigeration system for a loss of refrigerant charge.
45
What is the carbon monoxide limit in the flue gas of any appliance?
No more than 5ppm excess for a 1 hour period, no more than 24ppm over an 8 hour period.
46
Which manometer is the most accurate?
U2 Manometer.
47
What does a barometric damper do?
Incinerator single action opens one way, oil double acting opens in and out.
48
What three items does a combustion analyzer sample when testing efficiency?
CO2, O2, Excess air.
49
What is a draft gauge used for?
To measure flue draft and pressure drop across air filters.
50
What are the four types of efficiencies?
Combustion, Steady state, thermal, annual fuel utilization.
51
What does annual fuel utilization measure?
The amount of heat actually delivered to the enclosure compared to the amount of fuel supplied to the appliance in a full season.
52
Which test dial is used for clocking the meter?
The proving dial.
53
What are three conditions that could possibly cause low O2 in the flue gas?
Insufficient combustion air, burner over firing, low vent stack draft.
54
What is the purpose of the LED PCB?
To aid in the diagnosis of furnace faults.
55
What should you not do before reading the fault code?
Turn the power off.
56
What are possible reasons for pressure switches not closing?
Blocked vent pipe, tubing issues, fault inducer draft motor, dirty or worn inducer fan wheel.
57
What are possible reasons for a limit switch to open?
Plugged filter, ductwork restrictions, loose blower wheel, faulty blower wheel, faulty switch or connections.
58
Where are flame rollout switches located?
Beside the burners.
59
How is the flame sensor checked?
By the DC micro Amps flowing through it.
60
Are all HSIs 110V?
False.
61
What can an oversized furnace do to an HSI?
Shorten its life.
62
What is the maximum pressure a velometer can measure?
10"WC.
63
What should you do when balancing an HVAC system?
Start with all dampers in the fully open position.
64
What is the minimum amount of readings that should be taken when performing a rectangular duct traverse?
12 minimum, 64 maximum.
65
What is static pressure?
Potential energy or energy at rest.
66
What is total pressure?
The sum of all the energy exerted by the air stream.
67
What is velocity pressure?
The directional pressure exerted in the air stream.
68
What does a rectangular duct traverse consist of?
Dividing the cross-sectional area into equal sections and taking readings in the middle of each section.
69
What is a pilot tube used for?
For convenience and accuracy, combining static and total pressure into one instrument.
70
What is a velometer?
An airflow meter that takes readings in feet per minute (fpm) or meters per second.
71
What does an anemometer measure?
Air velocity directly in grills, louvres, exhaust hoods, and duct openings.
72
Who must change orifices?
A qualified ticketed gas person.
73
What are the final steps prior to completion of an HVAC system installation called?
"Start up."
74
What should you not do when starting the unit?
Attempt to start until all items on the start-up checklist are completed.
75
How are compressors mounted?
Internally spring mounted.
76
How many Schrader type service gauge ports does each independent refrigerant system have?
Three per circuit.
77
What is the purpose of a crankcase heater?
To prevent refrigeration migration and mixing with crankcase oil when the unit is off.
78
When is the crankcase heater normally on?
All the time, even when the unit isn't running.
79
What is recommended before starting compressors?
Energize the crankcase heater for at least 12 hours prior to start-up.
80
What happens if the compressor is rotating in the wrong direction?
The controls will stop and display a circuit failure to pressurize.
81
What do some three-phase units use?
Single phase fan motors.
82
How are all 208/230 Volt units factory wired?
For 230V power supply.
83
What must be done if a 208/230V unit needs to be connected to 208V?
Re-wire the transformer by moving the 230V connection to the 200V terminal.
84
What must units equipped with an evaporator fan conform to?
Minimum CFM requirements at all times.
85
What should you use when converting a unit for use with propane LP fuel?
An accessory liquid propane LP gas conversion kit.
86
What should you not do with units?
Operate without return air filters.
87
What do tachometers measure?
RPM and are the most accurate.
88
What are the two types of tachometers?
Contact type and non-contact type.
89
What is Strobatac?
A non-contact type of RPM counter.
90
What should you do if the correct blower speed is not obtainable?
Replace one or both of the pulleys.
91
What sizes are V belts stocked in?
From 17" to 100", increasing in 1" increments.
92
What does the draft safeguard switch (DSS) do?
Shuts off the gas valve if the vent gas gets too hot.
93
What are the two main systems for direct fired heater?
Make up air fan and a heater.
94
What is an airflow switch?
A single pole double throw switch that is switched by air pressure.
95
What may airflow switches need to be adjusted for?
Different pressure that occurs at different CFM.
96
What does the modulation gas system (Maxitrol) consist of?
A temperature selector dial, a discharge air sensor, an amplifier, and a modulation gas valve.
97
What is it called when the modulation gas valve is all the way open?
"High fire."
98
What is the flame sensor control (FSC) used for?
To monitor the flame.
99
What should you do if the FSC is locked out?
Reset the unit by pressing the reset button on the fire burner control.
100
What are the four steps required to change compressor rotation?
Turn power off and lock out, switch any two of the incoming unit power leads, turn on power to the unit, verify corrected compressor rotation.
101
What should the gas supply pressure range be?
5.5"-13"WC.
102
What should the gas manifold pressure be?
3.5"WC.
103
What are the six tools required for a start-up?
Manometer, volt/ohm meter, amp meter, tachometer, thermometer, standard hand tools.
104
What is the formula for calculating pulley speed?
Dm x Sm / Df = Sf.
105
What is the formula for calculating belt length?
OC = (Dm + Df) 1.57 + 2L.
106
What is the formula for calculating pulley size?
DM = DM x SF / Sm.
107
What does a blue flame indicate?
Perfect combustion.
108
What does a yellow flame indicate?
Unburned carbon and high carbon monoxide.
109
What does an orange flame indicate?
A dirty flame.
110
What do compressors handle?
No liquid.
111
What happens if the vent on the regulator is frozen?
Gas pressure would fluctuate, a term called hunting.
112
What does a reversing valve do?
Makes it a heat pump.
113
What does propane provide in terms of BTUs?
More BTUs; change orifice to 10"-11"WC.
114
What does each revolution of gas pressure change equal?
1"WC.
115
What are the signs of a worn belt?
Side wear on the belt.
116
A dual duct system is one that mixes air at the unit true or false?
False.
117
What are twelve components of a dual duct constant velocity (DDCV)?
Return air fan, fresh air damper, pre-filter section, pre-heat coil, filter section, supply air fan, hot deck heating coil, cold deck cooling coil, packaged refrigerant unit, humidifying section, zone mixing boxes, air system controls.
118
Does a dual duct variable air volume (DDVAV) system adjust hot and cold airflows without changing volume true or false?
False.
119
What is the need for a makeup air system?
Exhausting large amounts of air requires makeup air to prevent negative pressure.
120
What are the two primary types of makeup air units?
Indirect gas fired and direct gas fired.
121
What is the difference between direct fired MUA units and indirect fired MUA units?
Direct gas fired MUA has a gas burner installed directly in the outside makeup airstream.
122
What are two styles of direct fired MUA units?
Direct fired non-recirculating unit and direct fired recirculating unit.
123
What are the two main types of air source heat pumps?
Air to air heat pump and air to water heat pump.
124
What is the basic function of a heat pump?
Extracts heat from one place and transfers it to another.
125
How many cycles does an air source heat pump have?
Three: heating, cooling, and defrost.
126
Where is the heat source for an earth energy system located?
They use earth or ground water or both as a source of heat.
127
What are the two types of ground loop systems?
Open loop and closed loop systems.
128
What are the three main components of an earth energy system?
Heat pump unit, liquid heat exchange medium, air delivery system.
129
What is the difference between closed loop and open loop systems?
An open system uses underground water, while a closed-loop system recirculates its heat transfer solution.
130
What are two types of energy recovery systems?
Heat-recovery ventilators (HRV) and energy recovery (enthalpy recovery) ventilators (ERV).
131
How does a Heat Recovery Ventilator (HRV) work?
The stale warm indoor air from the home gives a large percentage of its heat as it passes through the heat exchanger on its way out of the building. The fresh cool outdoor air picks this heat up as it flows in through the heat exchanger. Ideally, no heat is lost.
132
What are two standard ways to distribute fresh air through a building using an HRV?
Through the ductwork installed specifically for the HRV (direct ductwork) and through the ductwork of a forced-air furnace system.
133
Why is balancing a HRV important?
An unbalanced system results in poor airflow and poor heat recovery and can lead to other problems, including an undesirable, continuous air-pressure difference between the inside and outside of your home.
134
What is the main difference between an HRV and an ERV?
The main difference is the way the heat exchanger works. An energy-recovery ventilator transfers a certain amount of water vapour along with heat energy, while a heat-recovery ventilator only transfers heat.
135
What does an ERV have that an HRV does not?
The rotating enthalpy wheel.
136
What is the first step in the sequence of operation for any heating appliance with electronic ignition?
Call for heat from the thermostat
137
What is the function of the CPU?
CPU contains electronic circuits that can execute a sequence of stored instructions called computer programs.
138
What is the sequence of operations for a high efficient furnace?
Call for heat R-W closes- 24V
The inducer motor starts- 120V
The pressure switch closes- 24V
The HSI energizes- 120V
Main valve energizes- 24V
Ignition takes place- flame proves 0.8secs
HSI de-energizes
Main blower energizes- 120V
Call for heat is satisfied R-W opens
Main valve de-energizes
Inducer motor runs a post purge and then shuts down - 5 second delay
Blower fan turns off 90-210 second delay
Furnace is now in standby
139
What is the sequence of
operations for a standard efficient
furnace
1. Call for heat
2. Gas valve opens
3. Main burner lights
4. Blower turns on
5. Heat is satisfied
6. Gas valve closes
7. Fan control is satisfied
8. Blower turns off
9. Furnace is back in standby
140
What is the name given to the
sequence of operations that take
place before the gas valve opens?
Pre purge
141
What are the following thermostat
terminals
RH
RC
W
Y
G
C
RH 24V power for heating
RC- 24V power for cooling
W-heat Relay or valve
Y- Cooling
C - Common
G Blower fan Relay
142
Name a component that is an
automatic or a remote control
device that uses one or more
initiating devices to operate or
control another device
Relay
143
What is the start up sequence of
operations from "call for heat" to
energize a ignition module
1. Call for heat
2. R-W terminals close
3. Energizes inducer fan Relay
4. Starts inducer fan
5. Pressure switch closes (air
pressure increase in response
to fan)
6. Allows power to flow to ignition
module
144
What does TDOD stand for?
Time Delay On De-Energization Relay
145
What happens to the contacts when the TDOD relay is energized?
The contacts change instantly
146
When do the contacts of a TDOD relay revert back to their original position?
After a specified time when the relay is de-energized
147
True or False: The contacts of a TDOD relay change position after a delay when energized.
False
148
Fill in the blank: A TDOD relay reverts contacts back to their original position only after a specified time when the relay is _______.
de-energized
149
Regarding relays, what
applications are SPST
and DPDT Used for?
For switching equipment off and on
150
Define a Relay
A Relay is a device or a remote
control device that uses one or
more initiating devices, such a
switch, to operate or control
another device connected either
in the same circuit or in another
circuit.They can be operated
electro-mechanically or electronic
solid state components
151
A typical furnace circuit board will only have one voltage. True or False?
False, it normally has 120V on the primary side of the transformer and 24V on the secondary side of the transformer.
152
How does a transformer create energy?
Through electromagnetic induction
153
What is the relationship between the number of wraps and voltage in a transformer?
The voltage ratio is proportional to the ratio of the number of wraps
## Footnote
For example, 120 wraps on the 120V side and 24 wraps on the 24V side
154
What is the primary mechanism through which energy is created in a transformer?
Electromagnetic field
155
What is the typical voltage input of a transformer?
120V
156
What is the typical voltage output of a transformer?
24V
