Final Flashcards
an obstructed expansion valve may be indicated by an incompletely cooled evaporator and
frosting at the evaporator inlet
when liquid reached the compressor of a fridge system through the suction line, the condition is called
flooding back (slugging)
the refrigerants referred to as CFCs are
fully halogenated
excessive oil foaming in the crankcase of a fridge compressor can result in
overheated compressor bearings
if you find an extremely large leak while using a halide torch, the flame will
go out
in a fridge system, the heat normally producing the flash gas at the TEV, is obtained from
the portion of liquid refrigerant which does not flash
what device will indicate proper operation of a fridge system dryer
moisture indicator
lube oil should have
a low pour point
a compound gauge is typically installed on the
suction side of a compressor
what is the safest device for testing for ammonia leaks?
litmus paper
increasing head pressure in a fridge system without any corresponding change in the cooling water inlet temp would prob be caused by
air and non-condensibles gases in the condenser
alkylbenzene is miscible and suitable for use with
r-22
if an expansion valve is adjusted for too a superheat value
too much liquid will be passed back to the compressor
during the operation of a large, multi-box system, using a fixed capacity compressor, only 2 of 5 boxes are being cooled. if 2 more boxes started cooling
low side pressure would temp increase
the water regulating valve installed in a system is operated by the
compressor discharge pressure
recovery small appliance after nov 1993
90%
constant superheat is maintained at the evaporator outlet of a coil by a
TEV
ammonia is lighter than air and if a leak should occur it’s concentration will be
of minimum importance during venting
air trapped in a system using a water cooled condenser is usually indicated by
unusually high head pressure when compared with existing temp of liquid refrigerant
foaming of the oil in a refrigerant compressor crankcase is caused by
refrigerant boiling out of solution from the lube oil
overcharging an air-cooled system will cause the
compressor to short cycle
the amount of refrigerant admitted to the evaporator is directly related to
the superheat of the refrigerant in the tail coil
during tests to on a compressor running excessively, it is determined that the refrigerated space temp is nearly normal, the suction pressure is slightly high, and the head pressure is low. you suspect
leak door gaskets
what occurs if the power element of a TEV fails
the valve will move towards the closed position
a shortage of refrigerant is indicated by
bubble in the sight glass
when opening or closing service and line valves you
must open the seal cap
a compound gauge measures
pressure and vacuum
what is an accepted method for testing a TEV
place the sensing bulb in ice water and warm by hand. observe flow through and temp change at suction line
when is oil reading most accurate
shutdown following a prolonged period of operation
1st step in repairing known leaking system
look for oil
if head pressure in reciprocating compressor is excessive
the high pressure cutout switch should operate before the relief valve
the rate of heat transfer from a hot region to a cold region is affected most by
temp diff between regions
moisture in refrigerant may
freeze on the expansion valve seat and reduce the flow of liquid refrigerant
the compressor has blown the shaft seal, what do first
secure compressor and close suction and discharge valves
what piping material is used in extra heavy duty systems
steel
liquid line, thermostatically controlled, solenoid valve operates in response to
temp of box
a system equipped with reciprocating compressor and water cooled condensing unit is overcharged, resulting in high head pressure caused by
refrigerant flooding the condenser
ammonia should be added at
the high side of system
small obstruction in TEV will result in
suction pressure fluctuation
refrigerant with oil in solution will
have a higher boiling temp at a given pressure than pure refrigerant
sight glass in liquid line will indicate
condition of refrigerant charge and moisture in system
how to prevent a system from working while under repair
lock out electrical circuit
compressor in air cooled system is short cycling on high pressure cutout switch because
system is overcharged with refrigerant
compressor in water cooled system is short cycling on high pressure cutout switch because
high pressure cutout switch is improperly adjusted
if temp of ammonia gas in discharge piping of condenser remains above 266 degrees F
vapor will cease to condense
units over 20 cu ft capacity require what for repair
a gas mask or SCUBA
overfilling a container is extremely dangerous because high pressure called
hydro-static pressure of expanding liquid
what valve should be closed when adding ammonia
king valve
when taking readings at suction service valve of operating compressor
temp and pressure is required as refrigerant is superheated
condenser cooling water regulating valve is directly controlled by the
compressor discharge pressure
what copper alloy is commonly used in heat exchanges and has high resistance to corrosion
cupro-nickel
what is a suitable replacement for r-11
r-123
to correct slugging and flooding
adjust expansion valve
excessive charge of refrigerant in air cooled system can cause
higher than normal discharge pressure with normal box temp
if a liquid line strainer becomes clogged, it will be indicated by
loss of refrigeration effect in box
when hot gas defrosting a system, to avoid slugging, use the
re-evaporator
refrigerant leaving the metering device is
saturated liquid/vapor mixture
recovered burned out refrigerant will be
sent to reclamation facility for processing
moisture is removed from cfc-12 using a recycler by
using a dehydrator cartridge
what is characteristic of the liquid charged power element used in a TEV
the sensing bulb is never emptied of liquid refrigerant
refrigeration system compressor crankcase sweating is an indication of
excessive circulation of lube oil through the system
what refrigerant will normally require water cooled compressor
ammonia
if a system is short cycling on high head pressure, you should
check for proper water flow through the condenser
noise in a compressor can be caused by
worn bearings and piston pins, slugging, too much oil in circulation
ammonia vapors can
cause death in low concentration, will dissolve in perspiration and cause burns, will burn or explode
r-12 is toxic when
in contact with an open flame
if discharge valves are leaking badly, the compressor will
run continuously
where is the greatest amount of superheat
the compressor discharge
a purge recovery system is used in a centrifugal air conditioning or fridge system to
purge non-condensible gases without losing refrigerant
if the suction line between the evaporator and compressor is frosting up, the cause may be due to the TEV
thermal bulb coming loose from the suction line
each pressure vessel containing refrigerants, which may be isolated, shall be
protected by a relief valve set to relieve at a pressure not exceeding the maximum allowable working pressure of the vessel
a multi evaporator coil unit is equipped with an evaporator back pressure regulating valve. it must be bypassed when pumping down for repair be reduced suction pressure would cause the valve to
close
how does a solenoid valve differ from a modulating valve
solenoid is open or closed, modulating is position by the electrical signal
what is essential when installing a new TEV
accurate temp and suction pressure gauge
the oil separator is located
between the compressor discharge valve and the condenser
the sensing bulb doesn’t need insulation if the bulb is installed
in the cooled air stream
high suction pressure in a compressor is caused by
the TEV be opened too wide
when replacing the TEV
apply light film of oil to prevent oxidation
temp in box is controlled by adjusting the thermostat connected to the
liquid line solenoid
when removing air from system, all refrigerant should be
pumped to reciever
leaking suction valves in a compressor are indicated by
higher than normal suction pressure
oil separators serve to
return oil entrained in vapor back to the compressor crankcase
constant hissing at the TEV indicates
a lack of refrigerant
chemical moisture indicators in a sight will
change color if there is moisture
if a relief valve opens on a compressor discharge line, it discharges high pressure vapor to
the suction side of the compressor
refrigerant entering the compressor is
superheated vapor
short cycling is
frequent starting and stopping
excessive oil foaming in crankcase will occur when
the compressor starts after a long idle period
TEV have what to change size
internal restrictors of different sizes
if suction pressure in a compressor is below normal, it may be
a fouled compressor suction strainer
if a compressor is short cycling on the low pressure cutout switch, the cause is
TEV strainer is fouled
compressor is short cycling on high head pressure, cooling sea water is 72 degrees
check for sufficient flow through condenser
low pressure cutout switch is actuated by
pressure changes in suction line
all systems are protected with a
high pressure cutout
temp in the evaporator coil depends on
refrigerant pressure in the evaporator
introduce refrigerant on low side through
suction service valve as vapor
what is not on the high side
accumulator
TEV bulb is located
neat evaporator coil outlet
safety heads in compressor are held by
heavy coil springs
cylinders are what max weight
50 lbs
