Dom Class Flashcards by Tarek Bakir

Vibersorbers installed…

Parallel to crankshaft,
highest probability of leak location
Not used on hermetic compressors

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Receiver charge

Must hold 90% of charge at 90F

Minimum 10% full at any time

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Winter charge

Additional charge for receivers due to low ambient condition

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Heat pump filter driers

Special non directional

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Filter drier Sight glass location

Immediately after filter drier to indicate full column of liquid. Especially when evap is at higher elevation than condensor

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LLSV always after filter drier, why?

Keeps filter drier on high side, prevents impurities from escaping during pump down

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Txv outlet position

Always up

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What type of txv is needed to eliminate the need for a CPR

Pressure limiting txv

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Where to discharge air on pull through evaporator

Towards opening to prevent air infiltration

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Another name for push through evaporator and location

Low velocity, center of room
HIGH HUMIDITY (flowers)

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Suction line solenoids, location, application and purpose

After EPR, large case with critical set points, used to avoid excessive pressure drops

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Accumulator location and and sizing

Close as possible to inlet. Sized based on tonnage of system

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When should you insulate Accumulators

Outdoors only, intent is to boil off remaining liquid refrigerant, insulated indoor could prevent this

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CPR location

Close as possible to compressor after accumulator

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Max temp before damage to compressor occurs

135F

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Head pressure control methods (3)

Fan cycling
Fan speed control
Condensor flooding

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Fan cycling monitors what and is most used on what system

Monitors discharge pressure or temperature

Most used on cap tube system

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Two types of fan speed controls

VFD and ECM motors

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Insulation thickness for freezer

3/4 or greater

Dom test said 5/8

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Insulation thickness for cooler

1/2 inch or greater

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High temp ac insulation thickness

3/8” or greater

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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)

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Suction lift unloading

Coil energized, oil pressure lifts lever, loads compressor cylinder
Uses oil pump

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Ideal evap Temperature Difference

8-10F

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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

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

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

Dom Class Flashcards

(89 cards)