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Liquid Slugging Contamination of Mechanical Refrigeration System
Flooded Start
Loss of Lubricant Compressor Overheating


High Head Pressure Refrigerant Charge Incorrect
Low Head Pressure  


Low Airflow Excessive Airflow
Uneven Airflow over Coil Low Refrigerant Supply
Uneven Refrigerant dist. to coil Circuits or to Cooler Circuits Low Water Flow in Cooler (water-cooling evaporator for Chillers)
Uneven Water Flow Through Cooler Low Refrigerant Supply to Cooler

Metering Devices

Evaporator Overfeed ("Flooding") Evaporator Underfeed ("Starvation")
TXV Hunting Distributor Nozzles (TXV Applications)

Refrigeration Cycle Accessories

Plugged Filter-Drier (Liquid Line) Wet Filter-Drier
Undersized Filter-Drier Crankcase Heater Inoperative
Oil Separator Float Valve Stuck Open 4-Way (reversing) Valve Damaged or Stuck-Cooling

Refrigerant Piping

Suction Line Sizing and Design Hot Gas Line Sizing and Design
Liquid Line Sizing and Design Refrigerant Condensate Line Sizing and Design
Flash Gas at Metering Device Inlet  

Component System Analysis

Troubleshooting Chart

General Problem Category Symptoms Possible Causes
Liquid Slugging

(Refrigerant or Oil)

-Noisy Operation -Inadequate Airflow Over Evaporator
-Excessive Vibration -Excessive Charge (with Fixed Metering Device)
-Overheating -Oversized TXV
-High Compressor Power Draw (kW) -Frosted Evaporator
-Compressor Failure -Crankcase Heater Inoperative
-Reduced Capacity -Pumpout Control Faulty
-High Saturated Suction Temperature -Flooded Start
-Compressor Does Not Pump Properly  
-Zero Suction Gas Superheat  
Flooded Start   -Liquid Line Solenoid Valve Stuck On
  -Crankcase Heater Off or Faulty
-See “Liquid Slugging” Symptoms -Improper Piping System Design
  -Pumpout Control Faulty
-Leaky Liquid Solenoid Valve
Loss Of Lubricant -Overheating -Flooded Start
-Mechanical Seizure -Floodback of Liquid Refrigerant
-High Compressor Power Draw (kW) -Oil Trapped in System
-Failure to Start  
-Noisy Operation
-Compressor Winding Thermostat Trips
-Compressor Intermittently Trips Off on Internal Motor Protection
Contamination of Mechanical Refrigeration System -System Valve(s) Stick -Improper Evacuation/Dehydration
-Compressor Does Not Pump Properly -System Leak
-Compressor Failure -Strainer-Drier Loaded
-Overheating of Compressor -High Temperature Break Down Oil, Refrigerant And System Materials
-High Compressor Power Draw (kW) -Carbonized Valves
-Discoloration of moisture Indicator in Liquid Line Sight Glass -Sludged System
-Sealed-Tube Refrigerant Test Shows High Acid and/or Moisture Content  
Compressor Overheating -Compressor Failure -Condenser Dirty
-High Compressor Power Draw (kW) -Inadequate Condenser Airflow or Water Flow
-High Compressor Casing Temperature -Excessive Evaporator Superheat
-Compressor Safety Winding Thermostat Trips -Electrical Line Current and/or Voltage abnormal or unstable
-Failure to Pump Properly -Loss of Lubrication
  -Undercharged or Overcharged System
-Liquid Slugging


High Head Pressure (Saturated Condensing Temperature or Saturated Discharge Temperature) -Compressor Cycles off Intermittently on High Pressure Switch while System Calls for Cooling -Faulty Head Pressure Control Device
-Compressor Cycles Intermittently on Compressor Motor Protection Switch -Dirty Condenser Coil
-High Saturated Condensing Temperature -Faulty Condenser Fan Motor
-High Discharge Gas Superheat -Extensive Fin Damage
-Compressor Overheats -Condenser Air Re-circulation
-Compressor Seizure -Dirty Condenser Fan
-Compressor Motor Burnout -Condenser Airflow Blocked
-High Compressor Power Draw (kW) -Prevailing Winds Prohibit Proper Airflow Across Coil
-Low System Capacity -Backward Condenser Fan Rotation
-Saturated Suction Temperature Normal to High -Slipping Condenser Fan Belt
-Excessive Condenser Water Flow Rate -Bent or Broken Condenser Fan Blade(s)
  -Scaled Water-Cooled Condenser Tubes
-Faulty Condenser Water Pump
-Damaged Water Pump Impeller
-Plugged Condenser Water Lines or Screens
-Condenser Water Valve Stuck Closed
-Cooling Tower Problems
-Condenser Vapor Locked by Undersized or Poorly Laid Out Refrigerant Condensate Line which Prevents Refrigerant from freely Draining to Receiver
-System Overcharged
-Noncondensible Gas Present
Refrigerant Charge Incorrect -High Head Pressure -System Overcharged
-High Liquid Subcooling
-Low System Capacity
-High Saturated Suction Temperature
-High Compressor Power Draw
-Low Head Pressure

-System Undercharged

-Low Saturated Suction Temperature
-Low System Capacity
-Low or Nonexistent Liquid Subcooling
-Flash Gas at Metering Device Inlet
Low Head Pressure -Low Saturated Condensing Temperature -Faulty Head Pressure Control Device
-Low System Capacity -Refrigerant System Leak
-Low Saturated Suction Temperature -Undercharged System
-Low Compressor Power Draw -Condenser Water Valve


Low Airflow -Low Saturated Suction Temperature -Dirty Evaporator Coils (no Filters?)
-Low Suction Gas Superheat -Badly Bent Evaporator Fins
-Low Saturated Condensing Temperature -Dirty Filters
-Low Compressor Power Draw (kW) -See 'Airside-Low Airflow Over Evaporator"
-Low Supply Air Temperature  
-Low System Capacity  
-High Space Air Temperature  
-Iced or Frosted Evaporator  
-Compressor Slugging  
-See 'Airside' for others  
Excessive Airflow -High Supply Air Temperature -Fan Motor Speed Set Too High
-High Saturated Suction Temperature -Wrong Fan Drive Package and/or Setting
-High Compressor Power Draw (kW) -Undersized Coil (Applied Air Handler)
-Noisy Air System Condensate Carriers Over Air Handler Drain Pan into Fan and Supply Ductwork
-Water Dripping from Fan and Supply Ductwork Near Air Handler
Uneven Airflow Over Coil -Low System Capacity -Bad Duct Design near evaporator Coil
-Low Saturated Suction Temperature -Coil placement improper
-Uneven Condensate Coverage over Coil Surface -Air Turbulence at Coil
-Uneven Coil Surface Temperature -Lack of Necessary Air Baffling near Coil
-Refrigerant Floodback to Compressor -Obstruction Within Air Handler
-Compressor Slugging -Obstruction in Ductwork Near Air Handler
-Mismatched Coil and Air Handler
Low Refrigerant Supply -Low System Capacity -System Undercharged
-Low Saturated Suction Temperature -Liquid Line Kinked or Crushed
-High Suction Gas Superheat -Evaporator Tube Crushed (especially return bends)
-Low Compressor Power Draw (kW) -System Refrigerant Leak
-Low Saturated Condensing Temperature -Malfunctioning Metering Device
-Measurable Temperature Drop in Liquid Line -TXV Power Element Low on Charge
-Visible Bubbles in Liquid Line Sight Glass -Undersized Metering Device
-High Supply Air Temperature -Undersized Distributor Nozzle
-Frosted or Iced Evaporator -Head Pressure Control Faulty at Low Outdoor Ambient Temperatures
-High Discharge Gas Superheat -TXV Plugged Distributor Oil Nozzle
-Free Water in System Forms Ice
Uneven Refrigerant Distribution to Coil Circuits or to Cooler Circuits -Low system capacity -Plugged Evaporator feeder tube(s)
-Low Saturated Suction Temperature -Kinked or crushed feeder tube(s)
-Little or No Suction Gas Superheat -Partially blocked distributor
-TXV hunts -Oversized distributor
-Compressor Floodback -Oversized distributor nozzle (applied air handlers)
-Compressor Slugging -Improperly installed distributor (applied air handlers)
-Uneven Coil Surface Temperature -Crushed evaporator tube (especially return bends)
-Uneven Condensate formation on Evaporator -Plugged evaporator (or cooler) circuit
-Frost on Some areas of Evaporator but not on others
Low Water Flow in Cooler -Low Saturated Suction Temperature -Chilled Water Pump
-Low Suction Gas Superheat -Faulty Pump Motor
-Low Saturated Condensing Temperature -Damaged or Blocked Pump Impeller
-Low Compressor Power Draw (kW) -Blocked Chilled Water Line or Valve
-Low Leaving Chilled Water Temperature -Water Baffle(s) in D-X Cooler misplaced blocking flow
-Low System Capacity -Excessive water scaling (flooded cooler)
-High Space Temperature -Reverse Chilled Water Pump Rotation
-High Temperature Drop Between Entering and Leaving Chilled Water -Blockage in Chilled Water piping
-Chiller shuts down Intermittently (even though thermostat calls for cooling) on low Leaving Water Safety Thermostat -Water flow control valve restricting Flow
Uneven Water Flow Through Cooler -Low System Capacity -(D-X) Cooler:

-misplaced or broken baffle(s)

-excess air in water system

-debris inside shell of cooler

-Low Saturated Suction Temperature
-Compressor Floodback
-Compressor Slugging
-High Leaving Chilled water Temperature -(Flooded Cooler):

-badly scaled water tube(s)

-kinked or crushed water tube(s)

-plugged water tube(s) or water box

-Low Temperature drop between Entering and Leaving Chilled Water
Low Refrigerant Supply to Cooler -Low System Capacity -System undercharged
-High Leaving Chilled Water Temperature -Head Pressure Control not working at Low Outdoor Ambient Temperatures
-Low Saturated Suction Temperature -Refrigerant System Leak
-High Suction Gas Superheat -Flooded Cooler

-refrigerant flow from condenser blocked

-cooler refrigerant supply valve stuck

-Low Compressor Power Draw (kw) -D-X Cooler:

-liquid line or accessories plugged

-liquid line kinked or crushed

-TXV power element low on charge

-TXV plugged or stuck

-refrigerant distributor or nozzle plugged

-electronic expansion valve faulty or microprocessor problem

-frost-pinched cooler tubes

-Low Saturated Condensing Temperature
-Space Temperature Too Warm
-Chiller Compressor Cycles on and off Intermittently on Low Pressure Switch

Metering Devices

Evaporator OverFeed ("Flooding") -High Saturated Capacity -System Overcharge (fixed metering device)
-Low Suction Gas Superheat -Oversized Metering Device
-Liquid Floodback -TXV Stuck Open
-Compressor Slugging -TXV Superheat setting too Low
-Compressor Overheats -TXV type wrong for Refrigerant in system
-High Compressor Power Draw (kW) -Uninsulated TXV sensing bulb in warm area
-Compressor Failure -Loose TXV sensing bulb
-Compressor Pumps improperly -Incorrectly located TXV sensing bulb
-TXV Hunts -Partial load too low for Metering Device
-Excessive Oil Circulating in System
-High Head Pressure (fixed metering device)
Evaporator Underfeed ("Starvation") -Low System Capacity -System undercharged
-Low Saturated Suction Temperature -Undersized metering device
-High Suction Gas Superheat -Plugged metering device
-Low Compressor Power Draw (kW) -Plugged distributor or nozzle
-Low Saturated Condensing Temperature -Undersized distributor or nozzle (TXV jobs)
-High Discharge Gas Superheat -Kinked or crushed capillary tube
-High Supply Air Temperature -TXV stuck in closed position
-Iced or Frosted Evaporator -TXV power element low on charge
-Wrong TXV for refrigerant in system
-Plugged or crushed TXV external equalizer line
-TXV superheat setting too high
-Incorrect TXV sensing bulb location
-Free water in system forms ice and blocks refrigerant flow
-Low head pressure (fixed metering device)
-Faulty head pressure control device
TXV Hunting -Saturated suction temperature oscilates High then Low, in a cyclical fashion -Oversized TXV
-Suction gas superheat oscilates high and low in a cyclical fashion -Improper part-load control operation loads TXV too lightly
  -Very light cooling load
Distributor Nozzles (TXV Applications) -Evaporator Underfeed (see symptoms above) -Undersized distributor Nozzle (quite unlikely on comfort work)
-Evaporator unevenly fed by refrigerant (see symptoms on evaporator sheet) -Oversized Nozzle
  -Nozzle not sized for load stability

-Faulty Part-Load control sequence for evaporator sections

Refrigeration Accessories

Plugged Filter-Drier (Liquid Line) -Starved evaporator symptoms (see evaporator sheet) -Dirty refrigeration system
  -Compressor cycles on low pressure switch -Improper evacuation/dehydration
    -Metal chips, scale, etc., in system from installation
Wet Filter-Drier -Moisture indication sight glass shows wet -System Refrigerant leak
  -Valves stick intermittently and system cycles off from internal blockage -Improper evacuation/dehydration
  -Sealed Tube test of refrigerant shows wet -Leaking water-cooled condenser tubes
    -Filter-Drier exposed to air before installation
Undersized Filter-Drier -Low system capacity  
-Low compressor power draw (kW)  
-Low saturated suction temperature -Bad design on field piping system
-Low saturated Condensing Temperature  
-High discharge gas superheat  
-Flash gas in liquid line sight glass  
-High liquid refrigerant subcooling  
Crankcase Heater Inoperative -Flooded Start:

-High Compressor power draw (kW)

-Noisy operation

-Excessive compressor vibration

-Overheating of compressor

-Never switched on
-Violent oil foaming (visible in compressor sight glass) -Heater element broken
  -Control Circuit problem
  -Electrical power or control connection loose or corroded
Oil Separator Trapping Oil -Oil level low on compressor sight glass -Sludge blocking oil separator float valve orifice
-High compressor power draw (kW) -Oil separator float assemble faulty
-Compressor overheating  
-Compressor noisy  
Oil Separator Float Valve Stuck Open -High saturated suction temperature -Debris at oil separator orifice keeps float valve from seating properly
-High saturated condensing temperature -Faulty Float assembly
-High compressor power draw (kW) -Liquid refrigerant migrates through separator to compressor oil sump at shutdown
-Flooded Start  
4-Way (reversing) Valve Damaged or Stuck-Heating -Low or no heating capacity -Sludge in refrigeration system
-Compressor cycles intermittently on internal overload -Acids in refrigeration system
-Compressor runs but low on heating capacity -Improper evacuation/dehydration
  -4-way valve leaks internally
Suction Line Sizing and Design -Low system capacity -Undersized suction line
-Low saturated suction temperature -Pinched suction line
-High compression ratio -Obstructed suction line
-Compressor overheats -Oversized suction line
-Compressor noisy -Suction line layout creates oil entrapment
-High compressor power draw (kW) -Suction riser oversized or improperly laid out
-Mechanical seizure of compressor  
-Compressor won't start  
-Compressor trips off on motor protection  
-Contaminated system  
-Compressor pumps inadequately  
-Suction line sweating -Lack of insulation on suction line
-Excessive suction gas superheat  
-High discharge gas superheat  
-Broken Suction line --Improperly laid out and/or supported near compressor
-Noisy line vibration  
Hot Gas Line Sizing and Design -Low system capacity -Undersized hot gas line
-High saturated condensing temperature -Pinched hot gas line
-High Compressor power draw (kW) -Obstructed hot gas line
-High compressor ratio  
-Compressor overheats -Oversized hot gas line (especially risers)
-Compressor noisy -Hot gas line layout causes oil entrapment
-High compressor power draw (kW) -Hot gas riser oversized
-Mechanical seizure of compressor -Hot gas riser laid out wrong
-Compressor won't start -Oil or liquid refrigerant backflow to compressor at shutdown or at low capacity
-Compressor trips off motor protection  
-Compressor pumps inadequately  
-Broken hot gas line -Ruptured (Failed) Vibrasorber
-Noisy line vibration -Improperly laid out and/or supported piping near compressor

Liquid Line sizing and Design

-Compressor noisy at startup after shutdown period -Lacking hot gas line check valve near condenser inlet. Liquid refrigerant lays on compressor heads
-Flooded start after shutdown -Valves damaged or broken from hydraulic forces caused by liquid on heads
-Compressor vibrates excessively at startup after shutdown period -
High compressor power draw (kW) after shutdown period  
-Compressor pumps inadequately  
-Flash gas at liquid line sight glass -Undersized liquid line

-Low saturated suction temperature

-Pinched liquid line
  -Low compressor power draw (kW) -Obstructed liquid line
-Low system capacity -
-High suction gas superheat  
Refrigerant Condensate Line Sizing and Design -Low system capacity -Condenser vapor lock from undersized line
-High saturated condensing temperature -Line layout prevents condenser from freely draining to receiver
-High discharge gas superheat  
-High compressor power draw (kW)  
Flash Gas at Metering Device Inlet