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Unit 23 exam

Unit 23 Exam ( Compressor's)
If the compression ratio of a system
with a reciprocating compressor decreases, the amount of
refrigerant pumped by the compressor ____.
a. will increase
b. will decrease
c. will remain the same
d. cannot be determined
Answer : A
If the suction valve in a reciprocating
compressor is leaking slightly, the ____.
a. cooling capacity will be reduced
b. flow rate of refrigerant through the system
will increase
c. compressor can overheat
d. both a and c
Answer : A
The clearance volume of a compressor
a. increases as the compression ratio increases
b. increases as the compression ratio decreases
c. decreases as the compression ratio increases
d. remains the same as the compression ration decreases
Answer : A
What could happen if a semi-hermetic
compressor is operated with the suction service valve backseated and the discharge valve frontseated?
a. The system will pump down.
b. The system will pump out.
c. The head of the compressor may blow off.
d. The compressor capacity will increase.
Answer : D
Liquid entering the compression
chamber of a reciprocating compressor can lead to ____.
a. damaged valves
b. damaged piston rings
c. damaged expansion valves
d. both a and b
Answer :D
Most of the heat energy in the suction
vapor entering the compressor is ____.
a. heat of compression
b. sensible heat
c. latent heat
d. defrost heat
Answer : C
The temperature of the compressed
gas leaving the compressor can best be described as ____.
a. cold
b. cool
c. warm
d. hot
Answer : D
The screw-type compressor is used
primarily in ____.
a. large industrial refrigeration and air-conditioning systems
b. residential air conditioning
c. small commercial refrigeration units
d. domestic refrigerators
Answer : A
Rotary compressors are used primarily
in ____.
a. large industrial refrigeration and air conditioning systems
b. residential air conditioning
c. small commercial refrigeration units
d. domestic refrigerators
Answer : D
The clearance volume of a compressor
cylinder is the ____.
a. amount of refrigerant vapor the compressor cylinder will hold during each stroke
b. volume by which the compressor is rated
c. volume of the space between the bottom of the valve plate and the top of the
piston at top dead-center
d. the total volume of the cylinder when the piston is at the bottom dead-center
Answer : C
The discus valve design is more
efficient than a flapper valve design because ____.
a. it allows a compressor design with less clearance volume
b. it operates with less spring tension
c. the amount of expanded vapor in the cylinder is greater
d. it will not allow liquid refrigerant in the cylinder
Answer : A
Which of the following terminal combinations would show an open circuit if the internal overload
device in a hermetic compressor should open due to excessive heat?
a. common to start
b. common to run
c. start to run
d. both a and b
Answer : D
The suction and discharge valves in a
reciprocating compressor open and close depending on the
difference in pressure across them.
Answer : True
Scroll compressors are becoming
popular because they can handle some liquid flood-back without
compressor damage.
Answer :True
The scroll compressor is one type of
reciprocating compressor.
Rotary compressors have pistons that
rotate inside the cylinders.
Answer : False
Rotary compressors have no clearance volume."
Answer : True
The sight glass on a semi-hermetic
compressor is used to allow light to enter the crankcase to keep
the oil warm.
Answer :False
The shell of a hermetic type
reciprocating compressor is in the low pressure side of the system.
Answer : True
The hermetic reciprocating compressor
motor is essentially made of the same materials as an open type compressor motor.
Answer : False
A bolted together motor-compressor
assembly is sometimes referred to as a semi-hermetic type.
Answer : True
The higher the rpm of a compressor, the higher the pumping efficiency.
Answer : False
SEER is calculated based on the total
amount of cooling (in BTU's) the system will provide over the
entire season, divided by the total number Watt-Hours it will consume.
Answer : True
Because a scroll compressor's has
fewer moving parts, it operates much quieter than other compressor designs and technologies.
Answer :True
The type of compressor that is driven
by a belt is the ________ compressor.
Answer : Open drive
Pistons are connected to the crankshaft
using_____ and ______.
Answer : Rods & wrist pins
When the piston reaches the top of its
stroke, it is called _______.
Answer : Top dead center (TDC)
The refrigerant trapped in the cylinder
when the piston reaches the top of its stroke is called _________.
Answer :Clearance Volume
A compressor that has the motor and
compressor in one housing that is welded together is called a _______ type.
Answer : Hermetic
A compressor that has the motor and
compressor in a housing that is bolted together is called a _______ type.
Answer : Semi-hermetic
Excessive heat and pressure on the oil
in a compressor can cause oil to break down and the formation of ____ and ____.
Answer : Carbon & Acid
The compression ratio for an R-22
compressor operating with 68.5 psig suction pressure and 260
psig heat pressure is ____________________.
Answer :
___________ is a bimetallic disc that senses compressor discharge temperature and opens at 270 degrees F.
Answer : 33. Temperature Operated Disc
____________ opens at approximately 400 +/- 50 psi differential between high
and low side pressures for R-22, and 500 to 625 psi differential for R-410A.
Answer : Internal pressure relief (IPR)
What are the four stages of a
Answer :1.Glycolys
2.formation of acetyl e COA
3.Critic acid cycle
4.Electron transport & chemiosmosisAnswer :
A decrease in suction pressure will
have what effect on a reciprocating compressor?
Answer :Higher compression ratios
What is the purpose of a head gasket
and a valve plate gasket?
Answer :. Maintain Pressure & seal the head & valve plate.
Can the suction valves and discharge
valves on a reciprocating compressor be open at the same time? Why or why not?
Answer : Yes
Why can't reciprocating compressors
pump liquid?
Answer : They are designed to pump vapor.
Why won't reciprocating compressors
handle liquid refrigerant as well as scroll and rotary types?
Answer : They are not as efficient,and scroll & rotary use less power to operate
What is the purpose of a crankcase
heater on a compressor?
Answer : To prevent refrigeration migration & mixing with crankcase oil.Prevents condensation of refrigerant in the crankcase
of the compressor.