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