Unit 23 Quiz Flashcards
If the compression ratio of a reciprocating compressor increases, the amount of refrigerant pumped by the compressor ________.
Will decrease
What component connects the piston to the crankshaft in a reciprocating compressor?
Connecting rod
Flank sealing takes place in a ______ compressor.
Scroll
The hermetic compressor shell is typically thought of as a _______ component.
Low side
Two-stage compression is not generally used until the compression ratio exceeds 10:1, often experienced with __________.
Low temperature refrigeration
What is the function of the compressor in a refrigeration system?
It is a vapor pump that converts low pressure low temperature vapor into high pressure high temperature vapor
Compute the compression ratio using 14.7 psi as the conversion factor when the suction pressure is -3.1 psig and the discharge pressure is 198.9 psig for a low temp system using R-404A.
True or false: A semi-hermetic compressor can be taken apart and serviced.
True
True or false: The screw compressor uses an open motor instead of the hermetic design.
True
True or false: Motors for hermetic compressors are manufactured with the same materials as standard electric motors that operate in an open-air environment.
False
True or false: The rotary screw compressor is another name for the rotary type compressor.
False
True or false: To keep refrigerant vapor from leaking over the top of the scrolls, tip seals are used.
True
True or false: The centrifugal compressor is a positive displacement type compressor.
False
True or false: High compression ratios above 12:1 are not recommended by most manufacturers.
True
True or false: Open drive compressors are manufactured in two styles, belt driven or gear driven.
False
True or false: The discus valve in a reciprocating compressor has a smaller clearance volume than reed/flapper valves.
True
True or false: The scroll compressor takes a fixed volume of gas at a suction pressure and then maintains the same gas volume to increase its pressure.
False
True or false: A two-step scroll compressor uses motor speed to control cooling capacity.
False
List four causes that may lead to liquid refrigerant entering the compressor.
Broken evap fan,
broken metering,
dirty air filter,
overcharging
Where would you check an open drive compressor for a possible refrigerant leak?
Shaft seal
An electric motor is connected to an open compressor that is rated for 50 tons using R-22 refrigerant. The drive pulley is 5 inches in diameter and spins at 3600 rpm. The compressor needs to run at 1750 rpm. What is the diameter of the pulley on the compressor?
(drive pulley size x drive pulley rpm = driven pulley size x driven pulley rpm)
A disengaging solenoid valve is used to vary cooling capacity in a scroll compressor. What is the external feature that distinguishes a digital capacity scroll compressor from a two-step capacity scroll compressor?
Solenoid valve, outside compressor
Used to suppress compressor pulsating noises.
Muffler
Holds the suction and discharge valves.
Valve plate
Belt or direct drive. Must have a shaft seal to keep refrigerant from escaping.
Open compressor
Determines the direction the gas entering the compressor will flow.
Refrigerant cylinder valves
What external feature on the exterior of a compressor identifies it as a two-stage compressor that will utilize the Y2 terminal in the thermostat?
Two electrical connectors on each side
Which compressor doesn’t have a clearance volume and is more efficient than a reciprocating compressor?
Screw, rotary, centrifugal
Why is it bad to start a hermetic compressor when it is in vacuum? Explain in detail.
Starting a hermetic compressor while in vacuum may cause an explosion due to
Terminal Venting
Which type of v-belt is better at dissipating heat when used around small pulleys?
Cog belt
A 3-phase internal thermal overload will disconnect all three of the overload contacts at the same time if a motor overheating problem occurs. What happens if only one of the overload contacts opens?
Two of contacts will remain in circuit, resulting in overheating and high current draw
