Commercial Refrigeration Ch 6
(Controls and Accessories)
Questions and Answers 100%
Correct
Commercial refrigeration thermostats that sense the box air temperature have a
temperature swing of about how many degrees? - ANSWER - 5 degrees
Why does a thermostat that senses coil temperature prevent frost build-up on a
medium temperature evaporator? - ANSWER - The thermostat knows when to go
into defrost.
What is the primary purpose of the cap on a service valve stem? - ANSWER - To
prevent dirt from damaging the packing when the valve is opened.
What are two troubleshooting procedures that can be performed by back-seating
the suction service valve? - ANSWER - Check reed valves and high back pressure
from overloading.
What will happen if the compressor is started with the discharge service valve front
seated? - ANSWER - The valve plate gasket will be damaged or even injure the
technician.
With both service valves front seated what is the basic procedure for replacing a
semi-hermetic compressor? - ANSWER - 1) Unbolt the service valves from the
compressor. 2) Remove the old compressor. 3) Set the new compressor in place. 4)
Rebolt the service valves. 5) Pull a vacuum on the new compressor. 6) Back-seat the
service valves. 7) You're ready to start it up.
What controls the pump down solenoid? - ANSWER - Thermostat
What will happen if the pump down solenoid is installed backward? - ANSWER - The
system will not pump-down and the compressor will not shut off.
, What is the primary function of a hot gas bypass valve? - ANSWER - Maintain a
minimum suction pressure at the compressor.
What is the primary function of a CPR valve? - ANSWER - Prevents compressor
overload during hot pull-down.
How long must the oil remain below its minimum pressure before the oil safety
control trips? - ANSWER - 120 seconds
Will the oil safety control trip if the compressor goes out on internal overload, and
why? - ANSWER - No, it won't trip because the overload cuts power to the oil safety
control.
What can you do to prevent nuisance tripping of the oil failure control from electrical
problems like "brownouts" (low incoming voltage)? - ANSWER - Install a current-
sensing relay.
What is the primary function of an EPR valve? - ANSWER - Keeps pressure up in the
evaporator.
What does "ZP" stand for on a Sporlan TEV? - ANSWER - A freezer valve that limits
the pressure to the compressor.
List the steps required to determine the maximum suction pressure a compressor
can handle, and to also set a CPR valve. - ANSWER - . Front-seat the suction service
valve. 2) Start the compressor when the evaporator is warm. 3) Open (back-seat)
the suction service valve slowly and watch the compressor amperage. 4) When the
compressor is drawing RLA, note the suction pressure. 5) This is the maximum
pressure the compressor can handle and is also the CPR valve setting.
Two cases are installed on one compressor. One is a 35° display case and the other
is a 50° display case. Which case would require an EPR? - ANSWER - The lower-
temperature case.
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