HVAC Final Exam Electrical For Air Conditioning
A typical motor is designed to operate within a(n) _______________% range of its rated voltage.
10
When using a low voltage T-stat for heating and cooling, when would there be a jumper between Rh and Rc? Select one: a. When using a single transformer system b. When heating with an oil boiler c. When heating with a gas boiler d. When using a two transformer system
A) When Using a single transformer system
A device that changes an input energy into mechanical motion.
Actuator
Control composed of two metals bonded together and formed into a particular shape.
Bimetal device
This motor is basically a PSC motor with a start capacitor and relay to drop out the start cap.It has a high starting torque
CSCR
This motor is not commonly found in AC units.It has a centrifugal switch or start relay to remove the start capacitor and start winding from the circuity once it reaches 75% of its rated RPM's
CSIR
This compressor is used in large commercial refrigeration systems over 50 tons. It uses impellers or wheels and has no valves or pistons and operates at high speeds
Centrifugal Compressor
Heavy-duty relay with parts that can be replaced.
Contactor
The present condition as it is measured
Control point
A circuit that responds to changes in the signals from sensors and issues signals to devices.
Controller
A relay activated by current running directly through it.
Current
A shaded pole motor has a high starting torque. Select one: True False
False
In a split phase motor the run winding has the greatest amount of resistance. Select one: True False
False
Most thermostats in the HVAC industry are 120 volts. Select one: True False
False
The contacts of a potential relay are normally open. Select one: True False
False
The sun heats the earth through conduction. Select one: True False
False
The marked terminal of a run capacitor should always be connected to the ________side of the circuit.
Line
Heavy-duty relay with built-in overload protection.
Motor starter
The difference between the desired and present conditions
Offset
This motor has a run capacitor wired in series with the start winding. T=No start relay or centrifugal switch is needed. The run capacitor reduces the current flow through the start winding so it can stay in the circuit
PSC Motor
Electronic relay that uses a thermistor to control the motor circuit.
Positive temperature coefficient (PTC)
Relay whose operation is based on cemf
Potential
This compressor is a piston type compressor used in domestic and commercial systems
Reciprocating Compressor
Device commonly used to start or stop another operation of another system component, such as a motor.
Relay
This compressor is small and light weight and uses blades or vanes to move the refrigerant
Rotary compressor
This compressor is used on large chilled water systems 20 tons and up. It uses the spacing between the lobes of the screws to compress the refrigerant and will operate smoothly even when its capacity is reduced to as low as 10%.
Screw Compressor
This compressor is the newest type of compressor and has no intake or discharge valves except a check valve on the discharge. It has very little wear and tear because it has so few moving parts.
Scroll Compressor
Reacts to heat by changing pressure, usually with a diaphragm or bellows.
Sensing bulb
Device that detects and responds to a stimulus, such as changes in temperature or pressure.
Sensor
The desired conditioned.
Set point
This motor is single speed or multi speed motor. It has low running and starting torque and has a run winding only
Shaded pole motor
Relay that uses electronic devices for switching
Solid-state
This motor has a run and start winding and the start winding must be protected. It has a low running and starting torque.
Split Phase motor
Reacts to heat by changing resistance, often to modify an electrical signal being measured by an instrument.
Thermistor
Reacts to heat by producing a voltage that generates a current in a complete circuit.
Thermocouple
Copper conducts heat better than glass. Select one: True False
True
Digital thermostats usually display temperature, time of day, programming and operating status. Select one: True False
True
The human body has resistance. Select one: True False
True
The starting capacitor is connected in series with the starting winding. Select one: True False
True
The starting winding is wound with finer wire than the running winding so it has greater resistance. Select one: True False
True
The voltage draw is more when the motor is starting than when it is running. Select one: True False
True
When a technician is taking a volt reading across a closed switch in an energized circuit what should the reading be? Select one: a. 0 b. OL c. Source Voltage d. Infinity
a. 0
When a technician is taking an ohm reading across a closed switch what should the reading be? Select one: a. 0 b. OL c. Some Number d. Source Voltage
a. 0
Three motor terminal are marked 1, 2, & 3. Using an ohm meter the resistance of the windings are; (1.5 ohms between 1 & 2) (3.5 ohms between 1 & 3) (5 ohms between 2 & 3) Which terminal is the common? Select one: a. 1 b. 2 c. 3 d. neither
a. 1
What is the common electrical service to a residential home? Select one: a. 240 V single phase 60 Hz b. 240 V three phase 60 HZ c. 208 V single phase 60 HZ d. 240 V single phase 50 Hz
a. 240 V single phase 60 Hz
The common unit of heat energy is the Select one: a. Btu b. Fahrenheit degree. c. ft-lb.
a. Btu
How is the starting capacitor connected to the starting winding electrically? Select one: a. In series. b. In parallel. c. Between the starting and running winding. d. It is not connected to either the starting or running winding.
a. In series
The start windings have: Select one: a. More turns than the run windings b. Fewer turns than the run winding c. The same number of turns as the run winding d. Larger diameter than the run windings
a. More turns than the run windings
What is Resistance? Select one: a. Opposition to current flow b. Electrical pressure c. Amperage d. Voltage applied to the circuit
a. Opposition to current flow
What is the definition of a (BTU) British Thermal Unit Select one: a. The amount of heat required to raise the temperature of 1 pound of water by 1 degree b. The amount of heat required to melt a ton of ice c. The amount of heat required to raise the temperature of 1 ton of water by 1 degree d. The amount of heat required to raise the temperature of 1 pound of water by 10 degrees
a. The amount of heat required to raise the temperature of 1 pound of water by 1 degree
If a motor winding shorts to ground what will normally happen? Select one: a. a circuit breaker will trip b. the motor will keep running c. the motor will speed up d. nothing. the current is only going to ground
a. a circuit breaker will trip
What is the main difference between a relay and a contactor? Select one: a. current carrying capacity b. a contactor can carry 20 amps or less c. A relay is energized all the time d. The color
a. current carrying capacity
The thermostat cooling anticiopator is energized when the air conditioning system; Select one: a. has cycled off b. is operating. c. is in the heating mode d. when the fan switch is in the "ON" position.
a. has cycled off
The US Customary unit of mechanical power is the ____. Select one: a. horsepower b. British thermal unit c. joule d. watt
a. horsepower
When current flows, a ___________ is produced around the conductor. Select one: a. magnetic field b. dielectric transmitter c. short circuit d. worm hole
a. magnetic field
In a transformer the ______________________ winding is the windings to which voltage is supplied and is considered the load side of the transformer. Select one: a. primary b. secondary c. start d. run
a. primary
Where does the "R" terminal of a thermostat connect to? Select one: a. transformer secondary b. transformer primary c. relay d. fan motor
a. transformer secondary
What is measured across an open switch Select one: a. voltage b. continuity c. current d. 0 volts
a. voltage
How many btu's make up one ton of refrigeration? Select one: a. 5,000 b. 12,000 c. 25,000 d. 100,000
b. 12,000
What does the "Y" terminal connect to on a wall mounted low voltage T-stat? Select one: a. Outdoor fan relay b. Cooling Contactor c. Primary side of transformer d. Indoor fan relay
b. Cooling Contactor
What device is added to a oil or gas forced hot air system when it is not AC ready? Select one: a. Fan limit switch b. Fan Center c. Multi Stage Thermostat d. Mars Relay
b. Fan Center
A clamp on Ammeter measures Select one: a. Voltage and resistance b. Magnetism c. Watts d. None of the above
b. Magnetism
When a technician is taking an ohm reading across an open switch what should the reading be? Select one: a. 0 b. OL c. Source Voltage d. Some Number
b. OL
What would be the cause of a transformer failure? Select one: a. Compressor amps too high for circuit b. Overloading the control circuit c. Underloading the control circuit d. None of the above
b. Overloading the control circuit
When testing the resistance of the windings of any motor what should you do if you obtain a measurable ohm reading to the motor casing? Select one: a. Replace the centrifugal switch b. Replace the motor c. Replace the starting relay d. Replace the run capacitor
b. Replace the motor
Heat travels from ______________to __________________ Select one: a. High pressure/Low Pressure b. Warm/Cold c. Low pressure/High Pressure d. Cold/warm
b. Warm/Cold
A cooling thermostat ___________________________. Select one: a. opens on temp. rise b. closes on temp. rise
b. closes on temp. rise
Contactors are rated according to the maximum amperage through the; Select one: a. coil b. contacts c. thermostat d. fuse
b. contacts
How are switches wired Select one: a. in the motor the start b. in series with the loads they control c. in series with voltages d. in parallel with the loads they control
b. in series with the loads they control
A substance's atoms ____ when heat is applied to the substance. Select one: a. move more slowly b. move more rapidly c. move into a crystalline formation d. stop moving
b. move more rapidly
When replacing a start capacitor the _____________should also be replaced Select one: a. run capacitor b. potential relay c. motor d. thermostat
b. potential relay
Snap action contact points are often used in controlling instruments to ____. Select one: a. decrease noise b. prevent electrical arcing c. maintain desired condition d. prevent motor from overheating e. replace any relays
b. prevent electrical arcing
With the fan switch in the on position, the indoor fan will,,, Select one: a. Run in cooling mode b. run continuously c. run only when the outdoor unit runs d. none of the above
b. run continuously
In a transformer the ______________________ winding is the windings to which the output voltage is supplied and is considered the source side of the transformer. Select one: a. primary b. secondary c. run d. start
b. secondary
Most start capacitors have a resistor soldered to the terminal posts to Select one: a. Rectify the applied voltage b. Smooth out the current c. Bleed the capacitor charge to reduce relay contact arching d. None of the above
c. Bleed the capacitor charge to reduce relay contact arching
To find the voltage of a circuit what formula is needed according to Ohm's Law? Select one: a. I= E/R b. R=E/I c. E= I X R d. None
c. E= I X R
What type of materials make good insulators? Select one: a. Copper, Gold, Silver b. Aluminum, Steel, Bronze c. Glass, Rubber, Plastic
c. Glass, Rubber, Plastic
What does the "G" terminal control on a low voltage wall mounted T-sat? Select one: a. Outdoor fan Relay b. Cooling Relay c. Indoor fan Relay d. Heat Relay
c. Indoor fan Relay
What is the most common type of T-sat in the HVAC industry? Select one: a. Line voltage b. Remote bulb c. Low voltage d. None of the above
c. Low voltage
When ohming out a load what reading should the technician get? Select one: a. 0 b. OL c. Some Number d. Source Voltage
c. Some Number
When ohming out a load what reading should the technician get? Select one: a. 0 b. OL c. Some Number d. Source Voltage
c. Some Number
When a technician is taking a volt reading across an open switch in an energized circuit what should the reading be? Select one: a. 0 b. OL c. Source Voltage d. Infinity
c. Source Voltage
PSC motors are commonly used for fans and _____________________. Select one: a. blowers b. inducer motors c. compressors d. house fans
c. compressors
Energy that is stored is called ____ energy. Select one: a. kinetic b. frozen c. potential d. sensible
c. potential
When checking voltage across a set of contacts while the coil is energized, you should read.... Select one: a. 120 volts b. 0 Ohms c. 208 volts d. 0 volts
d. 0 volts
The start capacitor must always be removed from the circuit when the motor has reached ____________ of its rated RPM's Select one: a. 10% b. 25% c. 50% d. 75% e. 95%
d. 75%
When installing a low voltage thermostat you should Select one: a. Use color coded wires b. Plug holes to prevent wall drafts from affecting the thermostat c. Maintain tight wire connections d. All of the above
d. All of the above
The internal overload of a compressor senses... Select one: a. Low voltage at the compressor b. Amperage draw of the control circuit c. Excessive fan motor amp draw d. Excessive amperage in the Compressor motor
d. Excessive amperage in the Compressor motor
What is the term used to descibe the output side of a transformer? Select one: a. Low inductive side b. High inductive side c. Primary side d. Secondary side
d. Secondary side
Testing the coil of a relay with an ohm meter provides an infinity reading. What is wrong? Select one: a. Voltage is still applied to the coil b. Meter needs a new battery c. The coil is okay d. The coil is open
d. The coil is open
What is Back EMF Select one: a. The voltage that powers the coil of a potential relay b. an induced voltage c. additional voltage found in the start winding d. all of the above
d. all of the above
What must be done before taking an ohm reading Select one: a. de-energize circuit b. isolate component c. set the meter to the proper scale d. all of the above
d. all of the above
Contactor coils are..... Select one: a. 24 volts b. 208 volts c. 120 volts d. any of the above
d. any of the above
The run capacitor gets wired in _______________ with the ______________ winding. Select one: a. seies, run b. parallel, run c. parallel, start d. series,start
d. series,start