Dom Class Flashcards
Vibersorbers installed…
- Parallel to crankshaft,
- highest probability of leak location
- Not used on hermetic compressors
Receiver charge
Must hold 90% of charge at 90F
Minimum 10% full at any time
Winter charge
Additional charge for receivers due to low ambient condition
Heat pump filter driers
Special non directional
Filter drier Sight glass location
Immediately after filter drier to indicate full column of liquid. Especially when evap is at higher elevation than condensor
LLSV always after filter drier, why?
Keeps filter drier on high side, prevents impurities from escaping during pump down
Txv outlet position
Always up
What type of txv is needed to eliminate the need for a CPR
Pressure limiting txv
Where to discharge air on pull through evaporator
Towards opening to prevent air infiltration
Another name for push through evaporator and location
Low velocity, center of room HIGH HUMIDITY (flowers)
Suction line solenoids, location, application and purpose
After EPR, large case with critical set points, used to avoid excessive pressure drops
Accumulator location and and sizing
Close as possible to inlet. Sized based on tonnage of system
When should you insulate Accumulators
Outdoors only, intent is to boil off remaining liquid refrigerant, insulated indoor could prevent this
CPR location
Close as possible to compressor after accumulator
Max temp before damage to compressor occurs
135F
Head pressure control methods (3)
Fan cycling
Fan speed control
Condensor flooding
Fan cycling monitors what and is most used on what system
Monitors discharge pressure or temperature
Most used on cap tube system
Two types of fan speed controls
VFD and ECM motors
Insulation thickness for freezer
3/4 or greater
Dom test said 5/8
Insulation thickness for cooler
1/2 inch or greater
High temp ac insulation thickness
3/8” or greater
Copeland unloading
Suction port is C OPE(n)lan D(energized) Unloading Copeland uses discharge as closing force Copelan(D) Carlyle uses electromagnet to close valves Carlyl(E)
Suction lift unloading
Coil energized, oil pressure lifts lever, loads compressor cylinder
Uses oil pump
Ideal evap Temperature Difference
8-10F
Importance of proper evap TD
Too high = frost build up
Easiest method of defrost
Manual defrost
Types of defrost methods (5 types)
Manual frost removal
Manual defrost
Off cycle defrost
Timed shut down
SUPPLEMENTARY DEFROST Water defrost Brine spray defrost Electric defrost Vapor defrost
Temperature operated defrost setting
35F cut it, 22F cut out
Accumulator sizing during hot gas bypass conventional flow (3 pipe system)
1.5 times system
3 pipe HGBP with re evaporator
Suction line Solenoid position and purpose during normal operation
Open to prevent excessive pressure drop
Max temp difference across 4 way valve
5F
Purpose of DPRV
Maintain pressure difference to ensure flow of refrigerant
Fin spacing colder vs warmer evap
Wider in colder
Closer on warmer
Manual frost removal equipment status
Running
Cooler application evap fan run time
24hrs
Another name for EPR
ORI
Open on rise of inlet
Hot gas bypass line connects at where
Between txv and evap
Grocery rack check valve location in relation to LLSV and purpose
Parallel, to send liquid back to liquid receiver during defrost cycle
Ammonia chemical make up and refrigerant designation
R-717
B2
NH4
Water refrigerant designation
R-718
Propane refrigerant designation
R-290
A3
R404a classification
A1
Pressure test duration and oxygen content
2 hour minimum, no more than 20%
Pressure relief valve rates by
Psi dry air
Above 400 lbs A1 (ammonia) or 200 lbs of all other refrigerants at 15 psi requires what
Relief to atmosphere (ammonia)
Restricted air flow causes what to the following Suction pressure Super heat Subcooling Compressor amperage
Decreased Suction pressure
Decreased Super heat
Decreased Subcooling
Decreased Compressor amperage
What happens to system if defrost cycle times out but doesn’t reach temperature
Defrost continues until DTS set point is reached then Pushes pin to end Defrost cycle
Define floodback
Liquid fed to compressor DURING cooling operation
Define flooded start
Liquid foaming on top of oil at start
Define slugging
Liquid in evap forced in to compressor at start (snot rocket)
Which ice contains impurities
Flake ice, used on foods
Purpose of harvest clutch
To detect when ice has fully separated from evap, NOT TO PUSH IT OFF
Water inlet pressure on ice machine
20-80 psi
50-75% of ice machine problems are what
Water related (dirty, pressure, drainage)
Ice machine condensor water temp
95-105F
Ice daily production formula
(1440 minutes/ cycle time) x weight of ice = daily production
How much ammonia is deadly in 10x10x10 room
1 tablespoon
Ammonia system capacity required for one skating rink
100 tons of cooling
3 best refrigerants in order
Water
Ammonia
Co2
All ammonia system requires what component
Oil separator
Oil cannot be reused
Once it leaves separator it does not return
Other names for tell tale
Oil pot and drop leg
Where oil collects at bottom of system
Water required to neutralize ammonia
10:1
Purpose of surge drum
To eliminate carry over of liquid ammonia to compressor. Suction line sloped 1/2” per 10 ft
Ammonia fire line requirements
Vent 25’ away from openings to building
Fire fighter valve located outdoors in red box 7’ above ground
Screw compressor max pressure
350 psi
Screw compressor parts
Male lobe, female flute
Screw compressor application
Air, gas, refrigerant, and natural gas processing
Ammonia recip compressor cooling
External
Ammonia oil cooled to what temp
120F
140F (bill)
Screw compressor unloading capability
Down to 10% capacity
Screw compressor compression ratio
2:1 to 20:1
Most efficient /least efficient ammonia evaporator
Liquid overfead/ DX coil
Screw compressor unloading force
Hydraulic, oil pump
TLV/TWA definition and application
Threshold limit value/ time weighted average
Refrigerant exposure effects during normal average work week
Pressure limiting vs pressure relief
Stop operation vs disposal of excess pressures
Occupational classification minimum distance to prevent grouping togeather
20ft
Safety group
A-B
1-3
Toxicity lowest to highest
Flammability lowest to highest
Stairwells
NO INSTALLATIONS EVER
Max size soft copper
1 3/8”
Permanently installed pressure guage rating
1.2 times design pressure (not operating pressure)
4 major location requirements of refrigeration equipment
1) permanent installed stair or ladder
2) sufficient clearance
3) 10 ft back from all edges (6 ft in ???)
4) if mobile equipment required, always on site and ready
Maximum amount of refrigerant in storage
300 lbs
Easy repair on compressor
Oil change and valve plate
Maximum compressor discharge temp
300F
Txv power element = ____ force
Opening
Severed bulb = closed shut
Pinched line = wide open or one setting (acts like hand expansion valve)
“Nominal” super heat settings
Ac = 15F Cooler = 10F Freezer = 5F
Nominal Condensing temp
30F above ambient
Oil breakdown temp
350F
Oil no longer lubricates at what temp
300-320
