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HVAC Pretest BOMAexam questions with 105- correct answers
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HVAC Pretest BOMAexam questions with 105- correct answers
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HVAC Pretest BOMAexam questions with 105-correct answers
Heat Transfer - ✔✔ANSW✔✔..Moves from one substance to another as well as
between molecules of a substance, temperature is the driving force
Oil safety switch - ✔✔ANSW✔✔..It is used to make sure that the compressor has oil
pressure when operating, opens on a rise in pressure.
High pressure switch - ✔✔ANSW✔✔..It is used to keep the compressor from operating
with a high head pressure, opens in a rise in pressure
Low pressure switch - ✔✔ANSW✔✔..It is a device that provides low-charge protection
and it also provides a control of space temperature, It also helps maintain the space
temperature in the cooler, closes in a rise in pressure
Planned Defrost - ✔✔ANSW✔✔..Is accomplished by forcing the compressor to shut
down for a short period of time so that the air in the cooler can defrost the coils, a timer
stops the compressor during times that the box is under the least amount of heat load
Random Defrost - ✔✔ANSW✔✔..Is the most common, will occur when the refrigeration
system has enough reserve capacity to cool more than the load requirement, and air in
the cooler will defrost the coil
Low Temperature Defrost - ✔✔ANSW✔✔..Is always planned defrost and because air in
the box is always below freezing heat must be added through internal heat (Hot gas) or
external heat ( electronic heater)
Electronic Heaters - ✔✔ANSW✔✔..Can have 3 to 5 defrost periods per day, of 45 to 60
minutes in duration, arent economical because the energy must be purchased for it,
they can also reach 300 degress F witch can burn components
Hot Gas Lines - ✔✔ANSW✔✔..Are economical because you are using internal heat
from the discharge line, but long lines can cause refrigerant to condense slowing the
defrost process, and liquid refrigerant could enter the compressor.
, Receivers - ✔✔ANSW✔✔..Located in the liquid line and is used to store liquid
refrigerant after it leaves the condenser.
Temperatures and Pressures For Refrigeration Components -
✔✔ANSW✔✔..Condenser discharge line should not exceed 225 degrees F, 278 psig,
liquid line should be 100 degrees F 278 psig, outlet of metering device should be 40
degrees F 69 psig, suction line should be 60 degrees F 69 psig
Sweating - ✔✔ANSW✔✔..Is caused by refrigerant overcharge and is a sign that liquid
may be entering the compressor.
Compressor Vacuum Test - ✔✔ANSW✔✔..Is a test to see if the compressor is
inefficient, reciprocating compressors should immediately go into a vacuum if the
flapper valve on the suction line is bad, a reciprocating compressor should pull 26 in to
28 in Hg vacuum
Condenser Splitting - ✔✔ANSW✔✔..Reduces the amount of extra refrigerant charge.
There are two valves, both are used for summer but only one for winter, because during
summer a larger surface area is needed to reject heat.
Condenser Flooding - ✔✔ANSW✔✔..Causes the refrigerant to move from the receiver
into the condenser, the excess refrigerant causes the head pressure to be higher than it
normally would be on a mild or cold day, which gives steady control in head pressure
EPR - ✔✔ANSW✔✔..Evaporator pressure regulating valve, is a mechanical control that
prevents the refrigerant pressure in the evaporator from going below a certain point, it
senses pressure and controls the flow of suction gas to the compressor, is located on
the suction line
CPR - ✔✔ANSW✔✔..Crankcase pressure-regulating valve, is used to keep a low-
temperature compressor from overloading on a hot pulldown
Hot Pulldown - ✔✔ANSW✔✔..Occurs when the compressor has been off for a long
enough time and the food has risen in temperature, and after a defrost cycle
Temperature - ✔✔ANSW✔✔..The level of heat or heat intensity, measured with
thermometers
Heat - ✔✔ANSW✔✔..Is the motion of molecules, and travels from a warm substance to
a cold substance
Conduction - ✔✔ANSW✔✔..Energy travelling from one molecule to another, involves
direct contact
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