Incorrect Final Exam #1 Flashcards
On single phase 3 wire circuits the correct conductor color coding could be red and black for line conductors and white for neutral. T or F?
True
The rated voltage on a run capacitor must be equal to or greater than the applied voltage to the compressor motor. True or False
False
MUST BE GREATER
The direction of rotation of a split phase induction motor can be changed by interchanging the two run winding leads. T or F?
True
You ohm a CSR compressor motor and obtain the following reading: Common to Run one ohm, Common to Start 2 ohms, Run to Start 3 ohms, each terminal to ground you read infinity. From this data, you determine the compressor is defective for the following reason:
- open run winding
- grounded start winding
- short between start and run windings
-turn to turn short in the start winding
d
You ohm a CSR compressor and record the following resistance readings: Common to Run one ohm, Common to Start four ohms, Run to Start five ohms, Common to Ground three ohms, Run to Ground four ohms, Start to ground one ohm. You decide to change the compressor because:
-the internal thermostat is open
-the run winding is open
-the start winding is grounded
- the run winding is grounded
start winding is grounded because it has the least amount of resistance to ground
(easiest path)
A PSC compressor has a shorted run capacitor. The compressor now has similar characteristics to which type of motor?
CSR
CSIR
RSIR
Three phase induction
RSIR
The voltage stamped on a run capacitor is:
- the system rated voltage
- always higher then system rated voltage
- equal to or greater then system rated voltage
-not significant
always higher than system rated voltage
A 240 volt three phase compressor motor is connected to the secondary of a 4 wire Delta Closed Distribution Transformer. One transformer is center tapped and grounded. What other voltages may be obtained from the secondary side of this transformer?
120/1/60, 208/1/60, 240/3/60
120/1/60, 208/3/60 , 240/1/60
120/1/60, 240/1/60, 240/3/60
120/1/60, 208/1/60, 240/1/60
d
The best trap for system contaminants as a result of a cookout is:
refrigerant
suction line filter drier
liquid line filter drier
refrigerant oil
refrigerant oil because it absorbs it and runs it through the system,
Which desiccant has the best ability to remove moisture?
methyl alcohol
activated alumina
silica gel
molecular sieve
molecular sieve
High discharge pressure can be caused by:
refrigerant overcharge
refrigerant undercharge
low load on evaporator
restricted cap tube
a and d
A low temperature commercial system is operating with a 10 degree f fluctuation in suction line temperature. This could be an indication of:
improperly adjusted metering device
undersized metering device
oversized metering device
oversized evaporator
oversized metering device or evap
An Air Conditioned computer room has problems with excessive static electricity with in the equipment. What could be the possible cause?
relative humidity too high
relative humidity too low
low temperatures
high temperatures
low temperatures
and
RH too low
A water cooled condensing unit has the following readings, water outlet temperature
98 degrees f, Condensing temperature of 128 degrees f. You determine that the unit:
operating fine
too much water flow through the condenser
too little water flow through the condenser
condenser may be fouling
condenser may be fouling
OR
too little (better answer)
A Up Flow Furnace would most likely be installed in :
the full basement of a two story building
the crawl space of a two story building
the attic of a single story building
the location of your choice
the full basement of a two story building
A Heat Pump can be Oversized by a Max of 35 % if the SPF is:
more than 2.25
less than 2
equal to 2.25
less than 2.25
less than 2.25
A Up Flow Furnace would most likely be installed in :
the full basement of a two story building
the crawl space of a two story building
the attic of a single story building
the location of your choice
the full basement of a two story building
Normally Add on Heat Pump Systems would be Turned off at approx:
45 degrees f
35 degrees f
the temperature stipulated by the utility
the calculated balance point determined by the work sheet for equipment selection
the calculated balance point determined by the work sheet for equipment selection
Define the Term U Factor.
Coefficient of thermal resistance
Coefficient of thermal conductance
Coefficient of thermal transfer
Coefficient of thermal insulation
Coefficient of thermal conductance
A current larger than normal, but flowing outside its normal current path is referred to as:
overload
overcurrent
short circuit
ground fault
short circuit
An overcurrent condition is:
a current above normal
a current shorted to ground
a short circuit
all of the above
all of above
A plug fuse with a continuous current rating of 25 amps will be identified by the color:
pink
blue
green
red
red
The voltage rating of a conductor is determined by:
the size of the conductor
the type of insulation around the conductor
the application of the conductor
there is no voltage rating on conductors
the type of insulation around the conductor
The term “slip” is used to indicate:
the amount of horse power lasted due to motor resistance
the amount of efficiency lost when there is no run capacitor
the difference in motor rpm between the time the start winding circuit is opened and when the motor reaches full speed
the difference between the motor full operational rpm rating and the actual speed under load.
the difference between the motor full operational rpm rating and the actual speed under load.
The purpose of a run capacitor as used with a split phase motor is to:
increase power factor
make the motor more efficient
increase starting torque
increase running torque
make the motor more efficient
You could replace a defective 35 uf, 370 volt running capacitor with which of the following capacitors:
35 uf 330 volts
35 uf 390 volts
30 uf 440 volts
40 uf 370 volts
35 uf 390 volts
A dual voltage three phase motor has a current draw of 50 amps when connected to a 240 volt line. How much current will flow if the motor is connected for operation on 480 volts?
25 amps
100 amps
50 amps
12.5 amps
25 amps
The primary and secondary winding of a transformer:
are wired in series
are wired in parallel
are not electrically connected
wired in series parrallel
are not electrically connected
A series circuit consists of three resistor. If one resistor is removed, and the remaining resistors are connected in series to the same source, then the current in each of these two resistors will be:
increased
decreased
the same as before
zero
increased
If an open occurs in one branch of a parallel circuit, the line current (total current) will:
increase and the total circuit resistance will decrease
decrease and the total circuit resistance will increase
decrease and the total circuit resistance will decrease
be zero and the total circuit resistance will infinity
decrease and the total circuit resistance will increase
Given the following capacitors , circle the most correct replacement for the following burned out start capacitor and run capacitor used on a compressor motor operating on a
208 Volts source.
Original
Start capacitor 190 - 220 Vac
140 - 165 MFD
190 - 240 Vac
140 - 175 MFD
400 - 440 Vac
140 - 160 MFD
230 - 345 Vac
140 - 165 MFD
340 Vac
300MFD
310 Vac
300 MFD
190 - 240 Vac
140 - 175 MFD
During overload conditions the solder melts. During short circuit conditions the fuse link breaks open. What kind of safety device do the preceeding statments describe?
A standard circuit breaker
A standard fuse
A time delay circuit breaker
A time delay fuse
A time delay fuse
When performing electrical tests of a compressor motor, what reading would you get if there was an open winding?
Low resistance
High resistance
Infinite resistance
No resistance
Infinite resistance
Who enforces the Canadian Electrical Code?
Electircal Trade Board
Electrical Safety Branch
Industry Training Committee
Canadian Safety Association
Electrical Safety Branch
CEC is a national code. What are the extra regulations required in BC called?
B.C. Amendments
Municiple codes
Municiple amendments
B.C. codes
B.C. Amendments
A coil of wire carrying alternating current produces a type of resistance known as:
inductance
capacitive inductance
capacitive reactance
impedance
impedance
Which of the following are two main types of thermostats?
extra-low and pilot duty
low and high voltage
low and line duty
extra- low and low voltage
extra- low and low voltage
A dual voltage three phase motor has a current draw of 50 amps when connected to a 240 volt line. How much current will flow if the motor is connected for operation on 480 volts?
25 amps
100 amps
50 amps
12.5 amps
25 amps
A current larger than normal, but flowing within its normal current path is referred to as an:
overload
overcurrent
short circuit
ground fault
overload
Extra-Low voltage thermostats would normally be used for which of the following applications:
residential air-conditioning
refrigerator thermostats
commercial Walk-in freezers
window unit Air conditioning units
residential air-conditioning
Which of the following is not an advantage of using pilot duty instead of line break control?
control cost is less
wiring costs are less
sized for light loads
large solenoids
large solenoids
An ammonia receiver has the following dimensions 36 inches dia x 60 inches long. What is the correct PRV size?
5 cu/ft/min.
5 lb./min.
7.5 cu/ft/min.
7.5 lb./min.
7.5 lb./min.
The gauge manifold set is a very important piece of equipment for the HVAC & R technician and may include:
compound gauge, high pressure gauge, manifold, hoses and manifold valves
either two or five valves
a five valve design including separate valves for evacuation and refrigerant charging
micron gauge
compound gauge, high pressure gauge, manifold, hoses and manifold valves
The hole drilled in sheet metal for a tapping screw should be the approximate size of:
the thread diameter
the thread root diameter
the shank diameter
hole diameter
the thread root diameter
A common aceptable filler material used for soft soldering is composed of:
50/50 tin-lead
95/5 tin-antimony
60/40 tin-lead
60/40 aluminium-tin
95/5 tin-antimony
A flux must be used when brazing:
copper to aluminum
copper to steel
steel to tin
copper to copper
copper to steel
The Code of Practice states that a brazing material will have a melting temperature between:
800-1600 °F
600-1200 °F
1100-1300 °F
600- 1200 °C
800-1600 °F
The crankcase pressure regulator (CPR) is installed in the suction line:
down stream from the suction accumulator under all conditions
down stream from the suction accumulator under certain conditions
up stream from the suction accumulator under all conditions
as close to the compressor as possible downstream of any other ancillaries in the system
down stream from the suction accumulator under certain conditions
Refrigeration systems frequently use liquid line filter driers to help remove any moisture trapped with the system after servicing. There are four common desiccants used in this accessory, but only two of the four are capable of also removing acids from the system. Which of the following are capable of acid removal?
activated alumina/silica gel
charcoal/silica gel
activated alumina/charcoal
molecular sieve/charcoal
activated alumina/charcoal
The setting (cutout) for a high pressure switch used on water cooled condensers should be higher than normal condensing temperature:
35%
10%
20%
depends on ambient temperature
20%
Which of the following materials are suitable for joining refrigerant piping?
silfos/silver solder (melting temperatures above 800 degrees f)
silfos/silver solder(melting temperatures below 800 degrees f
any material may be used (temperature has no relevance)
silver/95-5
silfos/silver solder (melting temperatures above 800 degrees f)
Choose the statement that describes latent heat of vaporization for a refrigerant.
it varies from refrigerant to refrigerant
it is a constant value for all refrigerants
its value is determined by the boiling point of the refrigerant
its value determines solidification
it varies from refrigerant to refrigerant
When examining a Psychrometric chart moving from left to right will on the chart will:
increase dry bulb temp and decrease relative humidity
increase dry bulb and increase relative humidity
decrease dry bulb and decrease relative humidity
decrease dry bulb and increase relative humidity
increase dry bulb temp and decrease relative humidity
The low voltage contacts on a room thermostat are:
in series with the load
in series with the cooling anticipator
in parallel with the cooling anticipator
in parallel with the heating anticipator
in series with the load
The purpose of a liquid line solenoid on a refrigeration system is:
to provide for pump down
to prevent liquid slugging
to prevent liquid flooding
to allow for the proper use of box thermostat
prevent liquid slugging
If you reduce the size of a water line supplying a water cooled condenser the result will be:
velocity will increase and pressure will remain the same
velocity and pressure will decrease
velocity and pressure will increase
velocity will increase and pressure will decrease
velocity will increase and pressure will remain the same
A chilled water system is equipped with two centrifugal pumps one for supply water the other for return water one of the pumps is leaking thought the packing gland. You decide to:
replace the pump gland
replace the other pump
tighten the gland packing
do nothing
do nothing
Which setting is adjusted first on a low pressure switch?
cut out
cut in
differential
cut out
Variable resistor such as a rheostat control current flow in a circuit? Yes or No
No
Rheostat is there to make a _______ drop not adjust current
voltage drop
Is a rheostat a load?
Yes
When installing evap train a liquid trap must be installed within the inside space. This is will limit heat infiltration from entering space. T or F?
False
When testing motor windings what scale would you use?
rx100
rx1000
rx10,000
rx10,000
How many leads for a part winding start motor compressor?
9 lead
If compressor is dead, but otherwise testing electrically OK. You may assume you have what kind of failure?
turn to turn short
TD on a high efficient condenser ?
15F
TXV valve may be + or - 25%-30%. True or False
True
TXV valves can be over or under sized within ___% - ___%
25% - 30%
Water cooled condensing unit temp TD is ___f average
10f
CPR is on which line?
suction line
CPR is downstream of suction accumulator and the purpose is to protect the compressor during hot pull down when discharge temp is high. True or False?
True
EPR is located on the suction line at outlet of warmest evap coil, upstream of controls/accessories. True or False?
True
EPR ____ on a rise of inlet
opens
CPR ______ on a rise of outlet to protect comp
closes
Set CPR based on compressor ____ during hot pull down
RLA
Best desiccants for acid removal? (2)
Charcoal and Activated Alumina
Best desiccant for moisture removal?
Molecular sieve
What letters represent these?
1.Coefficient of thermal resistance
2.Coefficient of thermal conductance
3.Coefficient of thermal transfer
4.Coefficient of thermal insulation
- R value
- U value
- ?
- ?
