CDC: 3E151 - HVAC/R JOURNEYMAN VOLUME 5

(801) How much sensible heat is added if the temperature of air increases from 70 to 80 F

10 F

(801) What occurs during the latent heat of condensation?

Vapor turns to a liquid

(801) What determines the pressure required to achieve a specific flow rate?

Design of the piping system

(802) What three processes take place in the condenser?

Desuperheating, condensing, and subcooling

(802) The heat being absorbed in the evaporator comes from the

product being cooled or the conditioned space

(803) What happens to the exhaust valve of a compressor during the intake stroke?

Backpressure from the high side closes it

(803) What effect do fins on the shell of a compressor have?

Increase surface area and allow more heat transfer with ambient air

(803) What does a check valve in the discharge line prevent with a rotary compressor?

Gas from leaking back to compressor

(803) Why must you be careful when placing meter leads on compressor terminals?

This is the weakest section of the compressor and a blowout could occur

(803) What is the result of a loose electrical connection at the compressor terminal?

Increased heat

(803) Where are internal motor protection devices embedded?

In or near the motor windings

(804) Desuperheating generally takes place in the

discharge line and first few coils of the condenser

(804) Non-condensables inside a refrigeration system are in what form?

Gas

(804) In a refrigeration system air gets trapped at the

top of the condenser and receiver

(804) What effect does counter flow have in a double-tube condenser?

Gives condenser a higher efficiency

(805) What is the relationship between a capillary tube metering device and refrigerant charge?

Using a capillary device makes the charge critical

(805) A filter strainer should be installed at the inlet of the capillary tube to

prevent dirt and foreign matter from clogging the tube

(805) In figure 1-41 where is the point of complete vaporization?

V

(805)When the evaporator pressure rises after the compressor stops the automatic expansion valve (AXV)?

closes

(805) What happens when a stepper motor expansion device receives a signal from the controller?

Rotates a precise, small amount

(805) An electronic expansion valve stepper motor's electronic controller receives a pressure reading from a

transducer in the suction line

(805) How does a pulse with modulating electronic expansion valve (EEV) vary refrigerant flow?

A signal quickly opens and closes the solenoid valve

(806) In an indirect expansion system the coil containing the secondary refrigerant is

in an air handler

(806) Dirt on an evaporator coil acts like

an insulator

(806) In a system using a capillary tube how does very little heat being absorbed affect superheat?

There will be little or no superheat

(807) Chlorofluorocarbon refrigerants are "doomed" because they

contain chlorine

(807) A low flow of refrigerant affects oil return to the compressor by causing

the refrigerant to lie on bottom of tubing

(808) What effect does friction have on the temperature of moving parts in an air conditioning (A/C) system?

Increases temperature

(808) How is oil forced to the main bearings when the pressure lubrication method is used?

A small pump of oil

(809) What affects the resistance of a thermistor?

Temperature

(810) Low voltage thermostats directly operate

solenoids, relays, and contactors

(810) What effect does an improper location of a thermostat have on the temperature being sensed?

It senses the wrong temperature

(811) What is the relationship between a liquid receiver and a system's refrigerant charge?

Liquid receivers are large enough to hold the complete system's charge

(811) What effect does a muffler have on a domestic refrigeration system's noise?

It breaks up the pressure pulses

(811) Insulating an oil separator prevents the refrigerant

vapor from condensing and returning to the compressor as a liquid

(811) Filter-driers are usually installed on the high-side between the

receiver and the expansion valve

(812) How do compressors with inverters vary the output capacity of the compressor?

By using an inverter

(812) What allows the technician to adjust variable frequency drive (VFD) parameters via a laptop?

Software

(812) Using the control strategy table from page 2-37, what frequency is being produced at step 10?

150 hertz

(812) According to the control strategy table on page 2-38, what is the output of the inverter compressor at step 16?

60 hertz

(812) What is the end result of the solenoid valve closing on a compressor with an internal unloader?

Intake valve held open

(812) How is discharge from one or more cylinders allowed to flow through a bypass line and into the suction line on a compressor with external unloaders and gas bypass?

A solenoid valve opens

(813) Which of the following is not a method of condenser capacity control?

Cycling compressor on and off

(813) Condenser flooding is necessary on cooler or cold days to

maintain constant head pressure

(813) What is the relationship between condenser flooding and the metering device?

Flooding ensures the metering device is receiving a constant liquid pressure

(813) What does the three-way solenoid react to in a system that uses condenser splitting?

Either outside ambient conditions or head pressure

(813) On a condenser splitting capacity control system, a three-way solenoid valve sends refrigerant to both condensers during warmer weather conditions because the refrigerant needs

more space to sustain proper head pressures and reject heat

(813) When airflow is used to control condenser capacity what effect does decreasing fan speed have?

Reduces capacity

(813) What effect does closing air dampers have on condenser capacity?

Reduces capacity

(814) What happens every 6 hours when a simple timed defrost system is set for an interval of 6 hours?

Defrost is initiated even if it is not needed

(814) Why do the compressor and evaporator fan not run during defrost?

The system should not be producing a cooling effect

(814) When does a time initiated, pressure-terminated defrost timer turn off defrost?

When evaporator pressure corresponds to the temperature the ice would have melted

(815) On a single temperature, multiple evaporator system the needs of each evaporator are controlled by a

low pressure motor control

(815) Where are evaporator pressure regulator (EPR) valves placed in a multiple temperature, multiple evaporator system?

In the suction line of the warmer evaporator

(816) What is a result of a clogged window unit's drip pan?

Condensate leak

(816) What is the relationship between a rooftop unit and its refrigerant charge as it is shipped to the job site?

Roof top units come factory-charged

(816) When ambient temperatures are low what does the economizer on a roof top unit do with outside air?

It uses the outside air to cool the space

(816) Using the outside air to cool a space is called "free cooling" because

it costs no money to cool the already cool outside air

(817) When a heat pump is in heat mode, heat transfers from the outdoor air to the outdoor coil because the

outdoor coil is colder than the outside air

(817) What is used to control the resistive heaters used with a heat pump?

Either a single-stage cooling or two-stage heating thermostat

(817) Where do the reversing valve's capillary lines at both ends of the cylinder of connect?

Pilot solenoid chamber

(817) When does the reversing valve's pilot solenoid pin carrier change position?

When the solenoid coil is energized or de-energized

(817) When both a thermostatic expansion valve (TXV) and a capillary tube are installed on a heat pump system, the TXV is used in a heat pump's winter operation because

winter conditions are less constant

(817) How do heat pump compressors handle some liquid slugging?

Using stronger internal valves and components

(817) What is the relationship between the outdoor fan's current draw during defrost and ice buildup on the outdoor coil?

More ice buildup means a higher current draw

(818) During a pre-operational inspection all electrical connections are checked

for looseness, corrosion, discoloration, or other signs of overheating

(818) What is checked for cleanliness during a pre-operational inspection?

The unit as a whole

(818) A spot of oil is a good indication of

a leak

(819) During an operational test what step is performed after you ensure proper power?

Amperage checks on motors

(819) What must be accounted for when using the pressure-temperature chart for an azeotropic refrigerant?

Temperature glide

(819) An assumption when reading pressure on the suction service valve with gauges is the pressure read at the suction service valve of the compressor is the same pressure at the

outlet of the evaporator

(819) When trying to detect non-condensables what is the next step after isolating the condenser?

Let condenser settle and reach ambient temperature

(819) When adding oil to a system what is the next step after closing the suction shut-off?

Stop the compressor and isolate it by closing discharge valve

(819) What is the final step when adding oil to a system?

Replace oil fill plug, run the compressor, and recheck oil

(820) Why should outdoor equipment in locations on the ocean's coast be serviced more frequently?

Ocean salt is airborne and is highly corrosive

(821) How could an inexperienced technician best locate various chiller components?

Manufacturer's diagrams

(821) How are chilled water pumps controlled?

Chiller controller

(821) On a centrifugal chiller system before entering the second stage impeller the vapors from the first-stage impeller mix with flash gas vapors from the

economizer

(821) Refrigerant is added on a centrifugal chiller system through a charging valve on the side of the

compressor

(821)What is the probable cause of large amounts of water collected by a centrifugal chiller's purge unit?

Leaky tubes

(822) Water in a closed-loop design geothermal heat pump that uses a well is discharged

at the bottom of the well

(823) How is the pressure plotted on the pressure enthalpy (PE) chart?

In pounds per square inch absolute (psia)

(823) At sea level, what is the absolute pressure if the gauge reads 20 pressure per square inch gauge (psig)?

34.7 pressure per square inch absolute (psia)

(823) The pressure enthalpy (PE) chart is based on how many pounds of refrigerant?

1

(823) On the pressure enthalpy (PE) chart a change in state takes place

inside the curve

(823) What is the condition of refrigerant on pressure enthalpy (PE) chart if the plot is on the right side of the curve?

Saturated vapor

(824) How many readings must be taken to fill out the pressure enthalpy (PE) chart?

7

(824) How are pressure enthalpy (PE) charts filled out if paper are not used?

Software

(825) How long should the system be allowed to run before measuring superheat?

Long enough for temperature and pressure to stabilize

(825) What is the next step for temperature readings after cleaning the pipe?

Take temperature at the outlet of the outlet of the evaporator

(825) What step is performed after converting the pressure reading to temperature?

Subtract saturation temperature from the suction line temperature

(825) What is determined before adjusting a thermostatic expansion valve (TXV) superheat?

The rest of the system is functioning properly

(825) What direction is the thermostatic expansion valve (TXV) adjustment screw turned to decrease superheat?

Counterclockwise

(825) Assuming everything else is working properly how is superheat decreased on a system with a capillary tube?

Add refrigerant

(826) How long should a system run before measuring subcooling?

Until temperature and pressure stabilize

(826) When measuring subcooling the next step after measuring pressure at the liquid line is to

convert the pressure reading up to temperature using the pressure-temperature chart

(826) Where is the high-side hose connected when using digital gauges to measure subcooling?

Liquid line service port

(826) What step is performed after adding refrigerant to decrease subcooling?

Read new superheat

(827) What is the first step when topping off a system with vapor?

Determine proper amount of refrigerant required by measuring superheat or subcooling

(827) After connecting the manifold gauge assembly (MGA) and hoses, what position are the service valves placed when topping off a system with vapor?

Mid-position