HVAC Vol 3

What relationship between magnetic field and conductors is required to generate voltage mechanically?

Relative motion between the two

Nickel and chromium alloys are used in heater elements because they

make it possible to operate the elements at high temperatures without melting

What effect does the length of a wire have on the amount of pressure needed to force the electrons to the load device?

More pressure will be needed

Resistance should not be considered a bad thing because

even conductors offer resistance to flow

All forms of opposition to current flow are measured in

ohms.

How is direct current produced?

By a battery or a thermocouple.

The sine wave gets its name because the alternator output voltage at any one point on the
wave is the product of the sine of the

rotor angle and the peak voltage.

What can you do to greatly increase the inductance of a coil?

Add a core of magnetic material.

Current lags the voltage in a purely inductive circuit because of the

opposition by inductive reactance.

When working with electrical equipment, how should you treat all electrical circuits as
being

live

How can you prevent anyone from accidentally closing the breaker to a circuit that is under
repair?

Lock the breaker in the OFF position and tag it to indicate that the system is being repaired.

If using an aluminum-clad wire in place of a copper wire, how many sizes larger must the
wire be to carry the same current safely?

One.

The type of insulation for a conductor is primarily based on

where it is going to be used.

What, if anything, does the location of a conductor affect?

Its current-carrying capacity

How is a solderless pigtail splice finished?

With a wire nut

When making a terminal loop, what will happen if the loop is not placed in a clockwise
direction?

The screw tends to spread the loop as you tighten it.

How is a stranded wire pushed into a push in connection?

Insert a small screwdriver into the slot.

How do you ensure the wire is placed tightly into a push-in connection?

By pulling slightly on it.

When checking voltage rating, what will result if you place two hot wires to the same side
of a device?

A direct short.

What could result if a circuit is forced to carry too much current?

A fire or electrocution

What is a common theme amongst schematics?

Different parts of the same component being separated.

On the Environmental Control Unit (ECU), what component should come on after the
compressor relay is energized?

Compressor.

What should you be doing as you follow each circuit on a schematic?

Describing in your head what is occurring with each component.

What is the key to understanding complex circuits?

Breaking down the complex circuits into smaller circuits and working through each in a logical
manner

What are you checking for when you troubleshoot a circuit using voltage?

The potential difference between two points.

How should you connect a voltage meter when checking AC voltage?

In parallel.

When testing equipment for high voltage, when should you connect your meter?

Before turning on power.

What should you do to the multimeter before checking for ohms?

Zero it out by touching the leads together.

What does it mean to isolate the part of the circuit you are testing?

Electrically disconnect the part being tested.

What tool should you use to test insulating material?

A megohmmeter

When taking current readings using the clamp-on ammeter, you squeeze the trigger
assembly to

open the clamping jaws and place the open jaws around one of the circuit leads

What effect does an open circuit have on the load device? The load device will

not operate.

What should you do if you are having problems troubleshooting?

Ask for help.

What is the next step after a part has been replaced?

Run an operational check

Where is a permanent distribution panel mounted?

In a wall or other frame structure in a facility or home

What happens to the circuit when a fuse blows?

It creates an open.

How does a magnetic-type circuit breaker open the circuit?

Instantly.

In a push-button switch, why are the push buttons insulated from the movable contact?

To avoid injury from electrical shock.

How must a snap-action switch close to avoid excessive arcing?

Quickly.

Which coil of a transformer is always connected to the incoming power?

Primary coil.

What is generated around the coil if AC flows through it?

An alternating magnetic field.

What happens when an alternating magnetic field is generated by one coil and cuts through
the turns of a second coil?

A voltage is induced in the second coil.

What happens when 24 volts is applied to a relay coil?

Contacts change positions.

What is the principal cause of a solenoids coil malfunction?

Excessive heat.

In a split-phase motor, if the start winding is not disconnected after a short period of time, it
will

burn up

How does the split-phase motor operate after the start winding is removed?

By the rotating magnetic field produced by the run winding and rotor.

How is a toggle switch wired with the hot conductor in the circuit?

In series.

What prevents the contactor chatter?

Shaded rings

When replacing a heater, how are they identified?

Catalog number.

The first step in removing an electric motor is to ensure the circuit breaker

or disconnect switch is open.

When an external-drive motor starts but hums, what is the probable cause?

A bad capacitor or centrifugal switch.

When troubleshooting motor failure, how do you determine if a motor is overloaded?

Perform a current draw with an ammeter.

What should the motor shaft be check for when troubleshooting motor failure?

Any up or down play

What does a meter reading of ohms mean when checking a circuit to a grounded surface?

A ground.

What could create excessive noise from the motor?

Motor not being securely mounted.

How can motor accessory noise be eliminated?

Tightening the oil well cover and connection box cover.

When checking coupling alignment, what should you do if any part of a coupling is
damaged?

Replace it.

How must the run windings be connected, to operate a dual-voltage motor on high voltage?

In series.

How do you change the rotation of a three-phase motor?

Change any two power leads.

Where are the load terminals connected in a three-phase controller?

T1, T2 and T3.

What contacts must close for supply power to be sent to the load circuit?

The normally open main contacts.

If an air compressor runs for an extended period of time, the oil in it will

heat up and turn into a vapor.

When oil from an air compressor carbonizes and solidifies, what problems, if any, can it
cause downstream?

Valves and air tools to malfunction

When you push the test button on the automatic drain of an air compressor, there should be
a blast of air and

a little moisture.

What happens to the vapor pressure inside a sensing bulb when the surrounding air
temperature increases?

It increases

What could occur if the system throttling range is too small?

Operator hunting.

In a timed on-off control, when does the heating anticipator cause the system to turn off?

Early before the space can overheat.

In proportional control, if the room is very cold, how much heat will the system provide?

An amount in proportion to the need

What is added to proportional control to correct its poor control and energy usage?

Integral action

How do valves and dampers move through their complete range of motion?

By an actuator that drives them.

In timed on-off control, what is the result of the controller not having to wait until it can
detect change in the control variable?

Control system lags have no significant effect.

In floating control, how does the controller move in relation to the deviation of the
controlled variable?

Its movement corresponds to the direction of deviation of the controlled device

What does a microprocessor do after it accepts inputs and stores them?

Creates a pre-programmed output.

What causes the temperature changes sensed by an averaging bulb?

Stratification.

What does a minimum position selector use to select its output?

The minimum output selected for that controller.

Where does an electronic actuator receive its direct current (DC) voltage?

From a controller.

What gives the engineers flexibility when creating customer comfort?

Variable frequency drives (VFD).

Where does the variable frequency drive (VFD) receive its feedback control?

Internally or externally.

What is required for the energy monitoring control systems (EMCS) and direct digital
control (DDC) components to communicate?

A modem at both locations.

Where can a technician make changes to a direct digital control (DDC) system?

From a computer in the shop or laptop in mechanical rooms.

What should be the state of outdoor air dampers during preoccupancy warm-up periods for
optimum start?

Inactive.

What air source does early morning purge use to precool a building?

Outdoor air.

What will a direct digital control (DDC) processor probably do after it receives its input and
processes the information?

Produce an output.

What proportional plus integral plus derivative (PID) action acts as a brake to stop the
controller at set point and prevent overshoot?

Derivative action.

What is a modulating signal from a direct digital control (DDC) to a particular device?

Analog output.

When the direct digital control (DDC) sends a small amount of current through the
thermistor circuit, what does it then do to the input current coming back from the thermistor?

Translates it into a temperature.

Why would you choose to install electric reheat over reheat water coils?

Electric reheat is cheaper to install.

On a central air-handling unit, which components turns on with the fan and also provides an
emergency shutdown feature?

Firestats and freezestats.

How many degrees Fahrenheit (F) above the normally expected temperature are supply duct
firestats set?

50.

Roll-feed media filters may be automatically controlled by

pressure-activated timer circuit

In a mixed-air system, if outdoor air temperature is higher than the conditions where free
cooling can be obtained, what will the outdoor air controller do?

Shut the damper

For space and zone control, where can the control of a coil come from?

The controlled space.

What type of relationship occurs if the reset variable increases and the primary set point
goes down?

Reverse.

What two things does a reheat subsystem control depend on?

Temperature and relative humidity

Besides cooling the air, what other function does the chilled-water coil do?

Dehumidify.

What must be used as the result of low relative humidity in the conditioned space?

Humidifier.

What can be used to prevent relative humidity in the duct from rising too high?

Sensor/controller

In a multiple-zone system, how can each zone draw as much hot or cold air as it requires?

By using an independently controlled set of mixing dampers provided for each zone.

In a multiple-zone system, the coil discharge temperatures are based on the

worst case zones (the largest heating and cooling loads)

By what percent can a hot deck increase operating cost if it was 10 degrees Fahrenheit warmer than
needed?

30.