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Technical Training Technical Training Technical Training Scroll Compressor Characteristics Scroll Compressor Characteristics Scroll Compressor Characteristics

Service Section Service Section Technical Training Technical Training December 2004 December 2004

Technical Training Technical Training Technical Training Scroll Compressor Characteristics Scroll Compressor Characteristics Scroll Compressor Characteristics

Scroll Compressor Scroll Compressor Failure Analysis Failure Analysis

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Failure Analysis Failure Analysis

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Why Do Compressors Fail In The Field? Why Do Compressors Fail In The Field?

• Too Hot

– Measure discharge temperature

• Too Cold

– Measure oil sump temperature – Measure discharge temperature

• Liquid Compression

– Use a crankcase heater

• No Oil Or Diluted Oil

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Summary Of 10 Returns Summary Of 10 Returns

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Overheating Overheating Overheating Overheating

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• Overheating Problems Occur When The Oil In

A Compressor Is Heated To The Point Where It Loses It’s Ability To Lubricate. If The Heat Is High Enough, The Oil Breaks Down Chemically

• Compressors Should Operate Within The Safe

Limits Of The Discharge Temperature

• Oil And Refrigerant Break Down In Severe

Overheating And Create CARBON And ACIDS, Which Can Cause Harm Throughout The Entire System

Overheating Overheating

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Example Of Overheated Compressor Example Of Overheated Compressor

Compressor Severely Overheated – Vacuum Operation

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• High Compression Ratios

– Low suction pressure

• Loss of refrigerant charge
• Blocked suction

– High discharge pressure

• Blocked Condenser
• Undersized Discharge Line
• Lack Of Sufficient Condenser Air Circulation
• Inoperative Fan Motors
• Refrigerant Overcharge
• Non-Condensables In The System
• Recirculation Of Condenser Air

– Combination of each

• High Return Gas Temperatures

– Insufficient insulation of suction lines

• Inadequate Compressor Motor Cooling

Causes Of Overheating Causes Of Overheating

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• 225°F / 107°C Discharge Line Temperature

MAXIMUM FOR DESIRABLE LIFE

• 250°F / 121°C Discharge Line Temperature

DANGER LEVEL - Oil Thins Out At 310-320 °F

• 275°F / 135°C Discharge Line Temperature

CERTAIN FAILURE - Oil Breaks Down Completely At 350 °F

The discharge line temperature will be 10 °F To 15 °F less than the internal temperature when measured about 6 inches from the service valve on the discharge line

Discharge Line Temperature Measurement Discharge Line Temperature Measurement

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• Watch For Undersized Evaporator Or

Oversized Compressor

• Check For Plugged Driers And Make Sure A

Solid Column Of Liquid Can Enter The Expansion Device

• Keep The Pressure Drop In The Suction Line

To A Minimum And Still Maintain Sufficient Velocity For Proper Oil Return

To Control Suction Pressure… To Control Suction Pressure…

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• Prevent The Suction Line From Passing

Through Hot Spaces

• Properly Insulate All Suction Lines Outside

The Refrigerated Space

To Control Return Gas Temperature… To Control Return Gas Temperature…

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Compressor Temperatures At Normal Load Compressor Temperatures At Normal Load

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High Load – Very Hot Weather High Load – Very Hot Weather

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Simulations Simulations

• To Identify Compressor Condition Due To

Blocked Suction Line

H.P L.P AMP

• Discharge pressure is a little lower than normal
• Suction pressure is very low
• Running current decreases

Pressure and running current reading

* Frost grows on evaporator coil

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Blocked Suction After 24 Seconds Blocked Suction After 24 Seconds

In 24 seconds, scroll temperature has risen by 87°C already above safe limit

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Blocked Suction After 48 Seconds Blocked Suction After 48 Seconds

Discharge line not very hot – Very low flow

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Blocked Suction After 96 Seconds Blocked Suction After 96 Seconds

Compressor already seriously damaged at this point. Power input is also rising.

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Blocked Suction After 118 Seconds Blocked Suction After 118 Seconds

Thrust face damaged Drive bearing damaged Thrust face damaged Scroll tips worn

Last data before protector trip

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• Corrections:

– Check system piping and components – Proper air flow across coils – Clean evaporator and condenser surface – Correct refrigerant charge – Insulate suction lines – Fan belt tightening sufficient – Short cycling of cooling air

Simulations Simulations

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Simulations Simulations

• To Identify Compressor Condition Due To

Charging Vapour Into Suction Line

H.P L.P AMP

• Both high and low pressures are very low
• Running current decreases extremely

Pressure and running current reading

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Split System Charging After 1 Minute Split System Charging After 1 Minute

Suction pressure:

• 0.5 bar = -7 psig

Discharge pressure: 6.9 bar = 100 psig (DLT) 64°C

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Split System Charging After 4 Minutes Split System Charging After 4 Minutes

Suction pressure: 0.1 bar = 2 psig Discharge pressure: 7.9 bar = 115 psig

Higher than the safe limit (175°C)

(DLT) 142°C

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Split System Charging After 8 Minutes Split System Charging After 8 Minutes

Suction pressure: 1.6 bar = 23 psig Discharge pressure: 14.4 bar = 209 psig

Much too high – Compressor damage

(DLT) 201°C

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Why Is LP Needed? Why Is LP Needed?

• LP Protects Against

– Blocked suction – Total loss of charge in off season – Slow vapour charging

• LP Acts Instantly And Stops The Compressor

– Damage can happen quickly – Temperature sensors on the outside of the pipe have some

delay

– Temperature sensors are influenced by the ambient

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Summary Of 10 Returns – Too Cold Summary Of 10 Returns – Too Cold

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Refrigerant Floodback Refrigerant Floodback Refrigerant Refrigerant Floodback Floodback

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• Occurs When Liquid Refrigerant Flows Through

The Suction Line Into The Compressor During The Running Cycle

• Small Amounts Of Liquid Refrigerant Enter The

Crankcase And Dilute The Oil In The Crankcase And Bearing Surfaces

– Irrespective of total system charge, excessive liquid

floodback leads to oil dilution

– This liquid will wash the oil off bearing surfaces – High oil dilution can result in bearing damage due to

inadequate lubrication

Refrigerant Refrigerant Floodback Floodback

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Oil Dilution Chart Oil Dilution Chart

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Example Of Refrigerant Example Of Refrigerant Floodback Floodback

Refrigerant floodback – Short body

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• Low Evaporator Loads

– Improper Sized Equipment – Poor Heat Transfer – Lack Of Air Circulation – Oil Logged Evaporator

• Improper Refrigerant Charge - Capillary Tube

System

– Overcharge On A Capillary Tube System Can Result In

Liquid Refrigerant Floodback

– Overcharge On TXV System Will Not Cause Liquid

Refrigerant Floodback

• Malfunctioning TXV

– Bulb location improper – External equilizer – Foreign material

Causes Of Liquid Refrigerant Causes Of Liquid Refrigerant Floodback Floodback

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To Prevent Liquid Refrigerant To Prevent Liquid Refrigerant Floodback Floodback

• Proper Air Flow / Air Distribution
• Proper Refrigerant Charge
• Ensure Adequate Superheat
• Use Adequately Sized Suction Accumulator

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Flooded Start Flooded Start Flooded Start Flooded Start

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• When A Compressor Is Started With Enough

Liquid Refrigerant In The Crankcase To Dilute The Oil And Overcome The Oil’s Ability To Lubricate Properly, A Condition Known As Flooded Start Exists

• The Refrigerant Gets Into The Oil During The Off

Cycle Through A Process Called Migration

• Damage Occurs When The Refrigerant Foam

Washes The Oil From The Bearings

Adequate Design Consideration Should Be Given To Prevent Refrigerant Floodback During The Off Cycle

Flooded Start Flooded Start

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Factors Affecting Refrigerant Migration:

• Length Of Compressor Off Time
• Compressor Ambient Temperature

– If the compressor is kept in a colder location, chances of

migration increases

• Temperature Difference Between The

Saturated Refrigerant In The Evaporator And The Oil In The Compressor

Flooded Start Flooded Start

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Example Of Flooded Start Example Of Flooded Start

Flooded start – No pressure

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To Control Flooded Start… To Control Flooded Start…

• Maintain Optimum Refrigerant Charge
• Use Crankcase Heater

– The crankcase heater must be turned on 12 to 24 hours prior

to initial starting the compressor

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Loss Of Oil Loss Of Oil Loss Of Oil Loss Of Oil

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Causes:

• Oil Pumped Out During Start-Up
• No / Little Return

Loss Of Oil Loss Of Oil

Symptoms:

• Excessive Compressor Noise & Vibration
• Excessive Amp Draw

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• Liquid Refrigerant Migration
• Liquid Refrigerant Floodback
• Poor Piping Connection / Design
• Improper / Insufficient Oil Trap
• Compressor Short Cycling

– Compressors must run long enough for the oil to be

returned

System Problems Leading To Loss Of Oil System Problems Leading To Loss Of Oil

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• Correct Piping Design And Eliminate

Improper Trap

• Correct Refrigerant Charge
• Check Control Setting To Prevent Short

Cycling

• Minimum Run Time

– Critical consideration

• Must run long enough to return oil to the compressor

after start up

Eliminating Loss Of Oil Failures Eliminating Loss Of Oil Failures

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Best Practice Best Practice

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How To Field Test A Scroll How To Field Test A Scroll

• Negatives

– Never close suction service valve – Never pump down into vacuum

• Never use the compressor to such oil into the system

– Never by-pass motor protector

• Teardown will show evidence
• Positives

– Run until system is stable – Measure suction and discharge pressures – Measure current – Check that suction, discharge, and oil temperatures are

normal

– Compare measured current with expected current – Current is very closely related to discharge pressure

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• Measure Suction And Discharge Pressures
• Measure The Amps And Volts
• Correct The Amps For Voltages Other Than

Nominal Voltage Using Formula

–

• Compare The Amp Value To Performance

Curve For The Compressor

• If Difference Is Greater Than 15%, Replace

The Compressor

Checking Compressor Efficiency Checking Compressor Efficiency

Voltage Rated Amps Measured x Volts Measured = Amps

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How To Check The Current How To Check The Current

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How To Check Suction Superheat How To Check Suction Superheat

• Measure Suction Line Pressure
• Convert Suction Pressure To Temperature

– Example: Take A = Saturated suction temperature

• Measure Suction Line Temperature, B
• Superheat B – A Should Be Above 5°C
• Example Calculation

– Pressure = 60 psig – Convert to temperature, A = 1°C – Suction line temperature, B = 10°C – Superheat B – A = 9°C

• This level is good

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How To Check Liquid How To Check Liquid Subcooling Subcooling

• Measure Liquid Line Pressure
• Convert Liquid Line Pressure To Temperature

– Example: Take A = Saturated liquid temperature

• Measure Liquid Line Temperature, B
• Subcooling B – A Should Be About 3°C
• Example Calculation

– Pressure = 270 psig – Convert to temperature, A = 50°C – Liquid line temperature, B = 42°C – Subcooling A – B = 8°C

• This level is too high indicating some overcharge

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Tools And Equipment Tools And Equipment

• Set Of Manifold Gauges

– Gauges can read saturated temperature

• Thermometer That Can Read Thermocouples Or

Multimeter That Can Read Thermocouples

• About 5 Thermocouples
• Scale

– Digital bathroom scale is accurate enough for commercial

systems

• Vacuum Pump
• Vacuum Gauge – Standard Gauges Are Useless

For Measuring Vacuum

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Vacuum Pump Line Losses Vacuum Pump Line Losses

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Effects Of Line Size Effects Of Line Size

Time Required To Reach 50 Microns On Dry Time Required To Reach 50 Microns On Dry 13 kg Tank: 13 kg Tank:

Long and Small Diameter Lines Wastes Time!

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Effects Of Effects Of Schraeder Schraeder Valves Valves

Time Comparison Of Different Vacuum Level Time Comparison Of Different Vacuum Level With / Without With / Without Schraeder Schraeder Core Core

Schraeder Valve Core Wastes Time!

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Ensure system is VACUUMED Use a SCALE Do NOT bypass safety devices Charge MAJORITY

• f refrigerant into

high side Charge ONLY liquid refrigerant Approximately 80% charge, start compressor Bleed balance LIQUID in through suction line STOP when sufficient charge achieved

Refrigerant Charging Scroll Compressors Refrigerant Charging Scroll Compressors

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System Charging Procedure Video System Charging Procedure Video System Charging Procedure System Charging Procedure Video Video

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Reverse Rotation Reverse Rotation

• Scroll Compressors Operate In Only One

Direction

• Three Phase Power Can Drive Compressor

Backwards

– If electrical leads are reversed

• Reverse Rotation Leads To Damaged Scroll

Forms

– Low mass flow is unable to remove heat

• Installers Must Ensure Proper Phase Direction

– Compressors will not fail immediately

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• Symptoms

– Suction pressure does not drop to normal level

• Discharge pressure does not rise to normal level

– Higher sound levels than normal – Current draw less than tabulated values – No pumping / compression – Compressor trips after several minutes

• Internal protection
• Correction

– Reverse any two of the compressor power leads – Re-apply power – If operating pressures does not become normal

• The reversing valve or the compressor is faulty

Diagnosing & Correcting Reverse Rotation Diagnosing & Correcting Reverse Rotation

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Removing System Components Removing System Components

• If Compressor Removal Is Required, Cut Out

The Compressor (Do Not Unbraze)

• Remove All Refrigerant Before Opening

System

– From both low and high side – Check with manifold gauge

• If Refrigerant Is Removed From High Side Only

– Can lead to scrolls becoming locked axially – Unbrazing is a fire hazard

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Temperature Limits Temperature Limits

• Discharge Line Temperature

– 2750F (1350C) extreme – 2500F (1210C) danger – < 2250F (1070C) desirable – > 450F (250C) above condensing temp

• Oil (Lower Shell) Temperature

– < 2000F (930C)

• TD (Temperature Difference) = Condensing

Temperature - Air Temperature

– < 20-250F (11-140C)

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Compressor Running But Noisy OK Suction P + T Was it always noisy? OK Discharge P + T OK Current Reverse Rotation?

Compressor Field Diagnosis Method Compressor Field Diagnosis Method

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Compressor With Module (Specter) Motor Overheat Discharge Temp Reverse Rotation? Current Discharge Press Suction Press Restart Fit Gauges OK Check Resistance Remove Wires from S1 S2 Check Connections And Continuity Thermistor Chain Problem (5 thermistor in Comp) Compressor Tripped

Compressor Field Diagnosis Method Compressor Field Diagnosis Method

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Compressor Not Running (For for internally protected compressor) Motor Burnt Motor Winding Open Cold Discharge Press Suction Press Reverse Rotation? Current Check Superht/Subcool Restart & Check System Fit Pressure Gauges Check Winding Resistance Cool With Water Turn Off Comp Protector Open Hot Compressor top Hot or Cold Yes OK Check Winding Resistance No Voltage On Compressor Terminal

Compressor Field Diagnosis Method Compressor Field Diagnosis Method

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