Unit 23 exam

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

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 scroll compressor is one type of reciprocating compressor.

False

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

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

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

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 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

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

Rotary compressors have pistons that rotate inside the cylinders.

Answer : False

The hermetic reciprocating compressor motor is essentially made of the same materials as an open type compressor motor.

Answer : False

The higher the rpm of a compressor, the higher the pumping efficiency.

Answer : False

A compressor that has the motor and compressor in one housing that is welded together is called a _______ type.

Answer : Hermetic

____________ 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)

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

A compressor that has the motor and compressor in a housing that is bolted together is called a _______ type.

Answer : Semi-hermetic

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.

When the piston reaches the top of its stroke, it is called _______.

Answer : Top dead center (TDC)

A bolted together motor-compressor assembly is sometimes referred to as a semi-hermetic type.

Answer : True

Rotary compressors have no clearance volume."

Answer : True

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

The shell of a hermetic type reciprocating compressor is in the low pressure side of the system.

Answer : True

The suction and discharge valves in a reciprocating compressor open and close depending on the difference in pressure across them.

Answer : True

Can the suction valves and discharge valves on a reciprocating compressor be open at the same time? Why or why not?

Answer : Yes

What is the purpose of a head gasket and a valve plate gasket?

Answer :. Maintain Pressure & seal the head & valve plate.

What are the four stages of a compression?

Answer :1.Glycolys 2.formation of acetyl e COA 3.Critic acid cycle 4.Electron transport & chemiosmosisAnswer :

The refrigerant trapped in the cylinder when the piston reaches the top of its stroke is called _________.

Answer :Clearance Volume

The sight glass on a semi-hermetic compressor is used to allow light to enter the crankcase to keep the oil warm.

Answer :False

A decrease in suction pressure will have what effect on a reciprocating compressor?

Answer :Higher compression ratios

Because a scroll compressor's has fewer moving parts, it operates much quieter than other compressor designs and technologies.

Answer :True

Scroll compressors are becoming popular because they can handle some liquid flood-back without compressor damage.

Answer :True

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 temperature of the compressed gas leaving the compressor can best be described as ____.

a. cold b. cool c. warm d. hot Answer : D

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 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

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