HVAC Quiz Review #1 Flashcards
What is the capacity of a cooling system rated in?
a) BTU
b) Ton
b) Ton
Heat energy is transferred down a metal rod by the process of:
conduction
Heat energy will be transferred from the flue gas to a heat exchanger by the process of?
convection
List the 4 different factors that will affect “human comfort”
- Temperature
- Humidity
- Air Movement
- Radiation
A typical heating system is is considered to utilize manual/automatic control
Automatic
What are the names of the two junctions on a thermocouple?
Hot and Cold
Approximately how many volts does a thermocouple produce?
26-32 mV
What is the difference between thermocouple and thermopile?
Thermopile creates more voltage and has more junctions
What are two different ways that a thermocouple could be used to prove the presence of a pilot flame, allowing the main burner to ignite?
Power Unit?
Lense -> Pyrometer
Thermistors would see their resistance increase/decrease when the temperature around them increases.
Decrease
What does RTD stand for?
Resistance Temperature Detector
1 BTU = the energy required to heat 1 ____ of water by ____ degree F
1 pound by 1 degree
How is heating energy measured in metric?
Calorie
Which temperature measuring device does not require physical contact with a heating source?
Pyrometer
Provide three examples of devices that sense temperature changes by physical movement
- Bimetal Type (strip, disc and spiral)
- Liquid Bulb Type
- Bellows Type
A fan control switch will be set at a higher/lower temperature than the high limit of a basic heating system
lower
Which heating devices should regularly have contacts open and close during normal operation
a) High Limit
b) Fan Control
c) Thermostat
d) Thermocouple
b) Fan Control
c) Thermostat
A basic heating system has the Fan-ON setting on low. What will occur?
Fan Cycling
What value is used to set the anticipator of a heating thermostat?
Gas Valve Current
The anticipator for a cooling thermostat is connected in series/parallel with the thermostat
Parallel
An older basic heating system would have connections for the thermostat on the gas valve. What are the connections named?
TH, TR, TH/TR
A modern mid-efficient furnace will have connections for the thermostat on the circuit board. Identify the function of each:
R - G - Y - W- C -
R - Power G - Fan Y - Cooling W- Heating C - Common
Another name for a high efficiency furnace:
Condensing furnace
Why must exhaust fans be interlocked with a make-up air system or furnaces
Prevent a negative air pressure or combustion gas
The contacts on a heating thermostat are closed. The indicates the room is above/below temperature.
below
List the cycle of operation for a mid-efficiency, gas-fired, forced air furnace.
- Thermostat contacts close, calls for heat
- Combustion air blower starts prepurge
- Air prove switch closes and igniter operates
- Gas valve opens and burner ignites
- Flame rod proves a flame and igniter is de-energized
- Heat builds in heat exchanger and plenum
- N.O. fan on time delay contacts close and fan blower starts
- Warm air forced through ducts until thermostat contacts open
- Gas valve de-energized, closes gas supply. Burner shuts down.
- Fan blower shuts down. Ready for next cycle
A basic gas fired furnace requires the 120V electrical to be connected in order for the pilot flame to function.
True or False?
False
What voltage reading should be expected across a flame roll-out switch?
0 V
What voltage reading should be expected across a high limit switch?
0 V
What voltage reading should be expected across a operating gas valve?
24 V
What device is used to prove the presence of a flame on a mid-efficient furnace?
Flame Rod
What are two methods to ignite the main burner on a high efficiency furnace?
HSI - Hot Surface Ignition
DSI - Direct Spark Ignition
The high limit on a basic gas fired furnace is connected in series with the ________.
transformer
The high limit on a high efficiency furnace is connected in series/parallel with the flame roll out switches.
Series
A gas valve is found to have a resistance of OL Ohms. What does this indicate?
Faulty gas valve, needs replacing.
The AFUE rating of a furnace is determined from the BTU-In vs the BTU-Out.
True or False?
True
The AFUE rating of a furnace could be improved by using higher efficiency electrical components.
True or False?
False
A high efficiency furnace will provide hotter air at the registers in a house versus a standard efficiency furnace?
True or False?
False - heat should be relatively the same
What would the “high” speed on a mid-efficient furnace blower be used for?
Cooling
A basic gas furnace can operate without a 120V connection?
True or False?
False
What would connect to a terminal labelled “EAC” on a furnace control board?
Electronic Air Cleaning
What would occur if the terminals “R” and “W” (on a furnace control board) were connected together with a short length of wire?
Heating cycle would turn on
The opening of a high limit on a basic furnace would cause the main burner and pilot flame to extinguish?
True or False?
False
What is the capacity of a heating system determined from?
a) Input BTU
b) Output BTU
a) Input BTU
