R-Pro

Refrigeration & HVAC field fault cases

565 real field cases — symptom, likely causes, what to check and what to do — collected by a working refrigeration technician. Every case is in R-Pro and opens offline.

By equipment

Field cases

• Unit Completely Inoperative
• Various Abnormal Noises During Operation
• Water Dripping from Indoor Unit / Poor Drainage
• Foul Odor When Unit Operates
• Inverter PCB IGBT Module Burnout (E6/H6 Error)
• BLDC Outdoor Fan Motor Burnout (Bearing Wear → Overcurrent Trip)
• PFC Circuit Electrolytic Capacitor Swelling (Increased Ripple Current → Capacitance Drop)
• Outdoor Fan Blade Crack/Break (Vibration → Shaft Imbalance → Motor Bearing Damage)
• Reduced Cooling Capacity — Unit runs but fails to cool adequately
• Frozen Evaporator — indoor coil blocked by ice buildup
• Outdoor Unit PCB Short Circuit from Moisture Ingress — Rainwater Entry, Damaged Waterproof Cover
• Infrared Remote Not Responding — pressing buttons causes no AC response
• Wi-Fi Remote App Connection Failure — smartphone app cannot find AC unit
• Indoor Unit Drain Backflow — water dripping from indoor unit onto floor or walls
• Flare Joint Refrigerant Leak — refrigerant leaking at pipe connection
• Indoor Unit Outlet Condensation → Ceiling Stains
• Multi-Split Distributor Pipe Sizing Imbalance → Capacity Deviation in Some Indoor Units
• Duct Leakage Exceeding 15% → Reduced Delivered Capacity
• Duct Internal Condensation → Insulation Delamination → Ceiling Water Leak
• Chiller Low Pressure (LP) Trip — Low Refrigerant or Expansion Valve Fault
• Unable to Reach Process Temperature — Chiller Setpoint Not Achieved
• Compressor Unresponsive Despite Start Command from Control Panel
• Oil Pressure Trip / Low Oil Level
• Water-Cooled Condenser Tube Fouling (ΔT >5°C)
• Air-Cooled Chiller High-Temperature Trip (Ambient >45°C)
• Screw Compressor Slide Valve Stuck (Partial Load Control Failure)
• Screw Chiller Oil Filter Clog (ΔP >0.15 MPa, Replace Every 2,000 Hours)
• Chilled Water Glycol Concentration Fault (Freeze Risk)
• Low Chilled Water Flow → Evaporator Freeze Protection Trip
• Chiller High Pressure (HP) Trip — Compressor Shutdown
• Primary/Secondary Pump Decoupler Reverse Flow — Bypass Piping Design Error
• Inverter Chiller Below 50% Part-Load — Efficiency Drop and Surge Risk
• VPF Variable Primary Flow Control Valve Hunting — PID Re-tuning and 40% Minimum Flow
• Multiple Chiller Sequence Control Imbalance — Operating Hours Rotation Failure
• Absorption Chiller Vacuum Loss — Non-condensable Gas Accumulation
• Absorption Chiller LiBr Crystallization Accident — Pipe and Heat Exchanger Blockage
• Centrifugal Chiller Surging — Repeated Impact Noise and Vibration
• Centrifugal Impeller Abnormal Vibration — Mass Imbalance or Bearing Damage
• Cold Storage / Freezer Temperature Rising
• Walk-in Evaporator Frost Buildup / Defrost Failure
• Cold Storage Compressor Failure to Start / Overload
• Moisture Contamination in Cold Storage System
• Freezer Floor Heating Cable Break → Floor Frost Heave
• Door Gasket Hardening & Shrinkage → Cold Air Leakage (External Condensation Worsening)
• Air Curtain Insufficient Airflow → 30%+ Cold Air Loss on Door Opening
• Insulation Moisture Infiltration → Thermal Performance Halved (U-Value Doubles)
• Door Frame Heater Failure → Frame Condensation → Ice Bridge Formation
• CO2 Transcritical System High Pressure Fault (Gas Cooler Control Failure)
• CO2 Dry Ice Blockage in Expansion Valve (Operation Below Triple Point)
• NH3 Refrigerator Oil Emulsification (Moisture Ingress)
• NH3 Leak Detector Alarm Response (25 ppm Warning to 500 ppm Evacuation)
• CO2 Cascade Intermediate Heat Exchanger (IHX) Excessive Temperature Deviation (-40°C Low-Temp System)
• Blast Freezer Food Core Temp Not Reaching -18°C
• Aging Room Humidity Control Failure (Unable to Maintain 85~95%RH)
• Ultra-Low Temp (-50°C) Two-Stage Compression Intermediate Pressure Control Failure
• Ethylene Buildup in Meal Kit/Produce Warehouse — Over-Ripening Due to Ventilation Failure
• Air Blast Cooler Fan Belt Wear → Reduced Airflow and Cooling Capacity
• Liquid Refrigerant Entering Compressor (Flooded Start / Liquid Slugging)
• Compressor Motor Burnout / Ground Fault
• High Compressor Discharge Temperature (>107°C scroll, >120°C recip)
• Scroll Compressor Reverse Rotation — 3-Phase Miswiring
• Scroll Tip Seal Wear — Volumetric Efficiency Loss and Reduced Cooling Capacity
• Scroll Poppet Valve Fails to Close — Reverse Rotation Noise After Shutdown
• Digital Scroll Solenoid Failure — Loss of 15% Capacity Modulation
• Scroll Internal Liquid Slug — Tip Fracture and Scroll Volute Crack
• Semi-Hermetic Reciprocating Reed Valve Failure — Loss of Compression
• Reciprocating Piston Ring Wear — Increased Blow-By and Oil Dilution
• Reciprocating Connecting Rod Bearing Scoring — Insufficient Oil Pressure
• Reciprocating Unloader Solenoid Stuck — Part-Load Capacity Control Failure
• Reciprocating Crankshaft Oil Pump Shaft Wear — Oil Pressure Below 0.15 MPa Trip
• Rotary Compressor Vane Spring Failure — Incomplete Suction and Volumetric Efficiency Drop
• Rotary Cylinder-Rotor Clearance Wear — Internal Leakage Causing Capacity Loss
• Open-Drive Compressor Shaft Seal Leakage — Oil and Refrigerant Loss
• Open-Drive Compressor Belt Tension Incorrect — Belt Slipping or Bearing Overload
• Open-Drive Compressor Coupling Misalignment — Radial and Angular Offset
• Open-Drive External Motor Winding Overtemperature — Thermal Protection Trip
• Open-Drive Compressor Crankcase Oil Level Drop and Oil Foaming
• Rotary Discharge Reed Valve Fatigue Failure → High-Side Backflow
• Twin-Rotary Phase Synchronization Failure → Abnormal Vibration Increase
• Insufficient Ice Production
• Ice-Making Cycle Repeated Restart
• Auger Motor Startup Failure
• Abnormally Long Ice-Making Cycle
• Cloudy or Opaque Ice
• Ice with Abnormal Odor or Taste
• Abnormal Ice Size
• Hollow Ice Cubes
• Ice Bridging in Storage Bin
• Water Supply Failure
• Water Supply Filter Clog
• Drainage Failure
• Full-Bin Sensor Error
• Ice Melting in Storage Bin
• Timer/Relay Malfunction
• Repeated Error Code Display
• Water Basin/Circulation Pump Slime Contamination
• Evaporator Plate Scale Accumulation
• Internal Odor / Pink Mold (Serratia marcescens)
• End-Zone Temperature Rise (Uneven Cooling)
• Air Curtain Weakening
• Excessive Temperature Rise After Defrost
• Excessive Heat Load from Direct Sunlight or Lighting
• Temperature Rise Due to Overloading Beyond Load Limit
• Excessive Evaporator Icing
• Defrost Heater Wire Break
• Defrost Termination Sensor Malfunction
• Frost or Water Droplets on Products
• Excessive Condensation from Not Using Night Cover
• Evaporator Fan Motor Burnout
• Condenser Fan Motor Failure
• LED Lighting Failure
• Hinge/Spring Wear — Automatic Door Closing Failure
• Double-Pane Glass Condensation (Internal Frost in Insulated Glazing)
• Defrost Water Drainage Blockage
• Evaporative Drain Fan Failure
• Electronic Controller (Dixell/Eliwell) Parameter Loss or Probe Error
• Partial Case Malfunction in Multi-Case Serial Network — Common Control Line
• 3-Phase Power Phase Loss/Voltage Imbalance — Compressor Overload Trip
• Cooling Tower Outlet Water Temp 3°C Above Design — Approach Deterioration
• Insufficient Cooling Capacity During Peak Summer Heat
• Fill Deterioration/Blockage — Reduced Heat Exchange Efficiency
• Spray Nozzle Blockage/Misalignment — Uneven Water Distribution
• Insufficient Fan Airflow — Belt Slip / Blade Pitch Misadjustment
• Condenser/Fill Scale Buildup — Reduced Heat Transfer
• Legionella Positive Detection — Hygiene Management Failure
• Steel Structure/Pipe Corrosion — pH Management Failure
• Excessive Algae/Biofilm — Insufficient Algicide or Sunlight Exposure
• Blowdown Malfunction — TDS Concentration Buildup
• Belt Slip / Break — Fan Stops
• Fan Motor Bearing Noise / Overheating
• Blade Pitch Misalignment / Damage
• Winter Basin Freezing — Heater Failure
• Drift Eliminator Damage
• Ground Loop Antifreeze Concentration Insufficient — Freezing / Poor Heat Transfer
• Reefer Truck Fails to Reach Setpoint During Driving
• Temperature Variation Inside Cargo Box — Uneven Cooling by Zone
• Poor Temperature Recovery After Door Opening
• Temperature Rise During Engine-Stop Standby Mode Switch
• Multi-Temperature Cargo Box Zone Failure — Partition Fault
• Diesel Engine Fails to Start or Shuts Down Prematurely
• Thermo King SR Controller Alarm Codes (00, 04, 17)
• Carrier Vector/Supra Compressor Unloader Failure
• All-Electric Reefer Inverter Failure
• Engine-to-Standby Auto Transfer Failure (ATS Fault)
• Cargo Box Insulation Degradation — K-value Rise
• Door Gasket Aging or Damage
• Data Logger / Temperature Recorder Inaccuracy
• Poor Re-cooling After Defrost Cycle
• GPS / Remote Monitoring Communication Loss
• EEV Stuck — Reduced Cooling/Heating Capacity
• Indoor Unit Drain Pump Malfunction Causing Water Leak
• Indoor Unit Fan Abnormal Noise and Vibration
• Remote Control Reception Failure — Commands Not Transmitted
• Horizontal Indoor Unit Airflow Louver Malfunction
• P/Q Communication Wire Open/Short Circuit — Indoor Unit Communication Error
• Central Controller Indoor Unit Recognition Failure
• DIP Switch Address Conflict Causing Indoor Unit Communication Clash
• Intermittent Errors from Electromagnetic Interference (EMI) on Communication Wiring
• BMS/Building Management System Gateway Integration Failure
• Reduced Cooling Capacity Due to Long Piping
• Poor Oil Return Causing Compressor Oil Shortage
• REFNET Branch Pipe Incorrect Direction Installation Causing Refrigerant Distribution Imbalance
• BS Unit Valve Malfunction During Simultaneous Cooling/Heating Operation
• Additional Refrigerant Charge Calculation Error During Commissioning
• Air-Cooled Condenser Fin Damage — Reduced Airflow
• Water-Cooled Condenser Tube Scale/Sludge — High Condensing Pressure
• Evaporative Condenser Spray Nozzle Clogging — High Condensing Pressure
• Condenser Fan VFD Control Fault — Condensing Pressure Hunting
• Air-Cooled Condenser Reverse Pressure Differential — Short-Circuit Backflow
• DX Evaporator Multi-circuit Maldistribution — Superheat Imbalance Between Circuits
• Shell-and-Tube Chilled Water Evaporator Tube Freeze Damage — During Winter Shutdown
• Plate Heat Exchanger Leak — Refrigerant and Chilled Water Cross-contamination
• Evaporator Coil Fouling — Dust Accumulation in Air-Cooled Indoor Unit
• Evaporator Pressure (SST) Dropping Below Design Value — Insufficient Air or Water Flow
• Filter Drier Moisture Saturation
• Receiver Tank Overcharge
• Sight Glass Bubble Formation
• Receiver Safety Relief Valve Leakage
• Filter Drier Clogged — 3°C+ temperature drop across drier
• TXV Sensing Bulb Gas Loss — Valve Fully Closed
• TXV Orifice Moisture Freeze-Up — Intermittent Suction Pressure Drop
• EEV Stepper Motor Coil Open Circuit — Resistance Test 40–80Ω
• Capillary Tube Blockage — Small Hermetic Refrigerators
• TXV Superheat Maladjustment — Hunting or Liquid Slugging
• Oil Separator Internal Filter Clog — Excessive Discharge Pressure
• Oil Return Line Check Valve Seized — Compressor Fails to Start
• Centrifugal Oil Separator Efficiency Drop — Oil Carryover from High-Speed Discharge
• Float-Type Automatic Drain Valve Failure — Continuous Oil Discharge
• Oil Separator Heater Open Circuit — Liquid Slugging at Startup
• Missing Oil Trap on Vertical Riser — Oil Accumulation
• Undersized Suction Line — Excessive Pressure Drop
• Oversized Suction Line — Oil Return Failure at Low Load
• No U-Trap on Discharge Line — Oil Backflow at Shutdown and Liquid Slugging on Start
• Double Riser Not Applied — Oil Stagnation at Partial Load
• Discharge Pipe Resonance Fracture — Excessive Support Spacing
• Coastal Copper Pipe Galvanic Corrosion — Aluminum Fin Contact
• Suction Pipe Insulation Peeling — Condensation and Ceiling Water Leak
• Brazed Joint Cold Cracking — Residual Flux Corrosion
• Pipe Fatigue Crack — Stress Concentration at Rigid Bracket
• Solenoid Valve Coil Open Circuit — Pump-Down Failure
• 4-Way Reversing Valve Slug — Heat Pump Mode Switching Failure
• Check Valve Back-Flow — Condenser to Evaporator Leakage
• Ball Valve Internal PTFE Seat Wear — Partial Leakage
• Service Valve Schrader Core Leakage — Gas Release When Connecting Gauges
• Compressor Anti-Vibration Mount Hardening → Vibration Transmission
• Outdoor Fan Blade Ice Imbalance → Vibration 4 mm/s or Above
• Discharge Pipe Resonance Audible Noise (500–1000 Hz Band)
• Indoor Unit Blower Bearing Wear → Characteristic Frequency Peak in Spectrum Analysis
• Compressor Liquid Compression Low-Frequency Pulsation → Pipe Rumbling
• Superheat Too Low (<3°C) → Liquid Slugging Into Compressor
• Superheat Too High (>15°C) → Capacity Loss & Discharge Overheating
• Subcooling Insufficient (<3°C) → Flash Gas in Liquid Line → TXV Hunting
• Subcooling Excessive (>10°C) → High Condensing Pressure & Efficiency Loss (Overcharge Suspected)
• EEV Superheat Sensor Misplaced or Uninsulated → Erroneous SH Measurement
• Hot Gas Defrost 4-Way Valve Fails to Shift → No Defrost
• Electric Heater Defrost Overtime → Evaporator Thermal Shock and Case Deformation
• Defrost Timer Interval Too Long → Increasing Frost Thickness
• Defrost Termination Sensor Failure → Premature or Excessive Defrost
• Drain Pan Heater Not Working → Drain Line Ice Blockage
• Economizer Valve Stuck → Efficiency Loss
• Floating Head Pressure Control Failure → Fixed High Condensing Pressure
• Heat Recovery Circuit Switching Failure → Waste Heat Loss
• Chilled Water Reset Control Not Applied → Overcooling & Excess Power
• VFD Fan/Pump Minimum Speed Set Too High → Excess Power Consumption
• Compressor Burnout After R410A→R32 Retrofit
• Oil Compatibility Failure During R22→R407C Conversion
• Gas Concentration Hazard Due to Poor Ventilation During R454B (A2L) Charging
• Existing Copper Pipe and Gasket Failure Due to R32 High-Pressure Incompatibility
• Mixed Refrigerant Charge Due to Identification Error — Missing Labels and No Analyzer Used
• Brazed Plate Heat Exchanger Freeze Fracture
• Shell & Tube Tube Sheet Leakage (Galvanic Corrosion)
• Air-Cooled Coil Fin Damage → Increased Airflow Resistance (ΔP Rise)
• Double-Pipe Condenser Refrigerant/Water Cross-Leakage (Pressure Test Identification)
• U-Bend Fatigue Cracking from Thermal Stress and Freezing
• Heating COP Drop at Low Outdoor Temp (Below -10°C)
• Discharge Air Temperature Below 40°C During Heating
• Excessive Frosting on Air-Source Outdoor Unit (Defrost Failure)
• Auxiliary Electric Heater (Backup Heater) Malfunction
• Refrigerant Undercharge/Overcharge — Winter-Specific Symptoms
• Cold Air Complaint During Reverse-Cycle Defrost
• Ice Buildup Under Outdoor Fan After Defrost — Drain Pan Heater Failure
• Defrost Entry/Exit Condition Error
• Excessive Defrost Frequency
• Hot Gas Defrost Valve Stuck
• 4-Way Valve Partial Switching — Heating/Cooling Mode Change Failure
• EEV Hunting — Unstable Superheat Control
• EEV Stepper Motor Miscalibration — Incorrect Valve Opening
• Ground Loop Flow Reduction — Air Entrainment / Cavitation
• Power Supply Fault
• Start Capacitor Failure
• Compressor Internal Failure
• Thermostat / Controller Failure
• Magnetic Contactor Failure
• Wiring Fault / Open Circuit
• Compressor Seizure / Lock-up
• Thermal Overload Protector Tripped
• No Cooling Due to Compressor Not Running
• No Cooling Due to Refrigerant Leak
• Expansion Device Blockage (TXV / Capillary Tube)
• Airflow Blocked by Excessive Frost Buildup
• Reduced Cooling Capacity Due to Condenser Fouling
• Reduced Cooling Capacity Due to Low Refrigerant Charge
• Cold Air Leakage Due to Faulty Door Seal/Gasket
• Excessive Cooling Load
• Compressor Anti-Vibration Mount Failure or Resonance
• Compressor Internal Bearing Wear or Oil Shortage
• Compressor Discharge Valve Leak Sound
• Evaporator Fan Blade Contacting Frost
• Evaporator Fan Motor Bearing Wear
• Condenser Fan Blade Deformed or Contacting Casing
• Condenser Fan Motor Bearing Wear
• Liquid Refrigerant Hammering (Liquid Hammer)
• Pipe Vibration / Resonance
• Immediate Trip Due to Ground Fault (Insulation Breakdown)
• Immediate Trip Due to Wiring Short Circuit
• Overcurrent at Start (Starting Device Failure)
• Start Capacitor Failure Causing Startup Overcurrent
• Intermittent Insulation Fault / Loose Terminal
• Motor Overload Due to Elevated Condensing Pressure
• Compressor Motor Overload (Winding Fault)
• Partial Frost Due to Expansion Device Abnormality
• Suction Pipe Frosting from Low Superheat
• Defrost Heater Open Circuit / Failure
• Re-frosting Due to Blocked Defrost Drain
• Defrost Timer / Controller Failure
• Short Cycling from High Pressure Protection Activation
• Short Cycling from Low Pressure Protection Activation
• Short Cycling from Overload Protector Activation
• Premature Cutoff from Thermostat Sensor Misplacement
• Malfunction Due to Control Board (PCB) Failure
• High Pressure Rise from Condenser Fan Stoppage
• High Pressure Rise from Condenser Fouling
• High Pressure Rise from Refrigerant Overcharge
• Non-Condensable Gas (Air) in Circuit
• Low Pressure Drop from Excessive Evaporator Frost
• Low Pressure Drop from Refrigerant Leak
• Low Pressure Drop from Expansion Valve Blockage / Closure
• Low Pressure Drop from Evaporator Fan Failure
• Fan Motor Control Signal Failure (PCB / Relay)
• Evaporator Fan Motor Burned Out / Faulty
• Fan Temporarily Stopped During Normal Defrost (Normal)
• Fan Power Wiring / Fuse Failure
• Condenser Fan Power Wiring / Contact Failure
• Fan Blade Jammed by Foreign Object or Bearing Seizure
• Condenser Fan Motor Burned Out / Faulty
• Condensate Around Condenser (Normal or Drain Issue)
• Condensate from Poor Pipe Insulation
• Drain Pan Contamination / Blockage
• Drain Hose / Pipe Blocked or Kinked
• Drain Pump Failure or Not Installed
• Distribution Panel Breaker Off or Tripped
• Partial Operation - Incomplete Power or Communication Error
• Internal Fuse / Miniature Circuit Breaker Blown
• Main PCB (Control Board) Failure
• Compressor Overheating from High Condensing Pressure
• Compressor Overheating from Excessive Suction Superheat
• Compressor Cooling Failure (Insufficient Motor Cooling Gas)
• Overcurrent and Overheating from Low Voltage
• Refrigerant Overcharge or Compressor Bearing Wear
• Motor Cooling Failure from Low Refrigerant → Overheating
• Poor Condenser Heat Rejection → Repeated Overheating Trip
• Oil Shortage (Low Oil Level)
• Low Oil Pressure from Overly Open Pressure Regulating Valve
• Oil Pump Failure
• Refrigerant Dissolved in Oil → Oil Foaming at Startup
• Valve Partial Failure Causing Re-compression and Oil Overheating
• Oil Contamination (Carbonization or Metal Particles)
• Ice Blockage of Expansion Device Confirmed (Moisture Freeze)
• Debris Blockage (Sludge or Welding Residue)
• Severe Moisture Ingress (Repeated Drier Blockage)
• Acid Contamination (Post Motor Burnout Circuit Contamination)
• TXV Sensing Bulb Poor Contact
• TXV Hunting Due to Fluctuating Load
• TXV Internal Defect (Diaphragm or Spring Fault)
• TXV Blockage (Debris or Moisture Ice)
• TXV Over-closure from Spring Over-tension or Bulb Gas Loss
• Refrigerant Overcharge or TXV Over-opening
• Inverter Overcurrent Error (Excessive Compressor Load)
• Inverter Error Code — Refer to Manufacturer Manual
• Inverter Instability from Pressure Abnormality
• Inverter Malfunction from Unstable Supply Voltage
• Inverter Overheating from Fouled Heat Sink
• Inverter Overheating from Overload Operation
• High Pressure Rise from Condenser Fan Failure
• High Pressure Rise from Condenser Coil Fouling
• High Pressure Rise from Non-condensable Gas (Air) in Circuit
• High Pressure Rise from Refrigerant Overcharge
• High Pressure Rise from Insufficient Cooling Water Flow (Water-Cooled)
• Poor Heat Transfer from Scale Buildup on Cooling Tubes (Water-Cooled)
• Cooling Water Temperature Rise (Water-Cooled)
• No Ice Production At All (Hoshizaki/Scotsman Cube Type)
• Compressor does not start
• Compressor thermal trip repeats
• Cooling temperature does not reach setpoint
• Excessive frost buildup on evaporator
• Abnormal noise from compressor
• Noise from condenser (outdoor unit) fan
• Refrigerant shortage (low suction pressure)
• Circuit breaker keeps tripping
• Electronic expansion valve (EEV) not responding
• Controller (board) displays error code
• Abnormal Superheat — Low / High Diagnosis
• Superheat Hunting — TXV Oscillation
• Superheat Cannot Be Measured — Gauge or Thermometer Reliability Failure
• Abnormal Subcooling — Low / High Diagnosis
• Zero Subcooling — Continuous Bubbles in Liquid Sight Glass
• PT Chart Usage — Pressure↔Temperature Conversion Diagnosis
• Refrigerant Type Cannot Be Identified — Missing Nameplate or Painted Over
• Manifold Gauge Connection Procedure — Standard Work Order
• Normal Operating Pressure Ranges — Reading Against Ambient Temperature
• Manifold Zero & Accuracy Calibration — Reliability Check
• Abnormally High Discharge (High-Side) Pressure — 4 Major Causes
• Abnormally Low Discharge (High-Side) Pressure — Diagnosis & Response
• Discharge Pressure Fluctuation — Pulsation, Oscillation, Cyclical Changes
• Compressor Short Cycling — Rapid ON/OFF Repetition
• Condenser Fan Short Cycling — Intentional vs Faulty Operation
• Refrigerant Overcharge — Symptoms, Diagnosis, Recovery to Spec
• Refrigerant Undercharge — Symptoms, Diagnosis, Leak Check
• Mixed or Wrong Refrigerant — Identify and Recover Immediately
• Refrigerant Recovery and Recharge Procedure — Standard Workflow
• Drain Clog — Condensate Overflow / Indoor Unit Leak
• Condensate Pump Failure — Motor, Float, Control
• Insufficient Drain Slope or Reverse Slope — Gravity Drainage Fails
• Drain Trap / Line Freezing — Cold Environment Blockage
• External Condensation on Drain Line — Insufficient Insulation
• New Refrigerants PT Chart — R-32 / R-454B / R-744 (CO2)
• Altitude Correction — Pressure Adjustment for Mountain/Highland Systems
• Subcooling Fluctuation — Hunting/Instability Diagnosis
• Confirming Overcharge with Subcooling — Most Reliable Diagnostic
• PT Chart — Glide refrigerants (R-407C / R-410A / R-454B) dew/bubble temperature difference in detail
• PT Chart — invalid below 0 PSIG (vacuum range), use micron/vacuum gauge instead
• Superheat near 0°C + suction line sweating/icing — Liquid Floodback emergency response
• Superheat behavior at low load — distinguishing normal from faulty
• Abnormal subcooling from condenser fouling/tube blockage — trim diagnosis
• System vacuum test with manifold gauge — procedure and pass criteria
• Short cycling — frequent ON-OFF after defrost
• Short cycling — aged thermostat or chattering contacts
• Short cycling — contactor or relay coil chatter
• Short cycling — low refrigerant charge causing low-pressure cutout/restart loop
• Suction pressure at low load — distinguishing normal from faulty (low load ≠ low charge)
• Abnormally high suction pressure — distinguish flooded, overcharge, compressor efficiency loss
• Discharge pressure pulsation — root causes and muffler/accumulator diagnostics
• Discharge line noise — pressure-based diagnosis vs simple listening
• Compressor bearing wear — vibration/noise/current/oil four-axis diagnosis
• Compressor motor overheat — internal overload (Klixon) tripping and root-cause diagnosis
• Compressor oil acidity test — using an Acid Test Kit and interpreting results
• Compressor fails to start — branching by hum, sustained LRA, or instant trip
• Heavy rumble/vibration noise — separating bearing wear vs mount failure vs system-side vibration
• Oil separator — operating principle, inspection points, common faults
• Oil return design — suction-line traps, riser velocity, double risers
• Reading the oil sight glass — normal vs faulty patterns and stage-by-stage interpretation
• Oil mist lubrication — operating principle, faults, and system loss mechanism
• Oil type mixing risks — mineral, POE, PAG, PAO and the compatibility matrix by refrigerant
• Refrigerant identifier kit — usage, result interpretation, and alternative identification methods
• Refrigerant cross contamination — system / recovery tank contamination scenarios and remedy
• Non-condensables — air/nitrogen entering the system, diagnosis and removal
• Refrigerant recovery equipment (machine, tank, scale) — use, maintenance, fault diagnosis
• Flammable refrigerants (R-32, R-454B, R-1234yf, R-290) — A2L/A3 classes, handling safety, recovery, work rules
• AC New Install — Evacuation and Vacuum Decay Test Procedure
• AC New Install — Flaring and Torque Tightening Procedure
• AC New Install — Nitrogen Pressure Leak Test (Low/High Side)
• AC New Install — Refrigerant Charging by Weight (R-32/R-410A)
• AC New Install — Refrigerant Line Insulation and Condensation Prevention
• AC New Install — Power Wiring (Single-Phase, Three-Phase, Dedicated Breaker)
• AC New Install — Indoor/Outdoor Communication Cable (Shield, EMI)
• AC New Install — Indoor Wall Mounting (Concrete, Drywall, Anchor Torque)
• AC New Install — Outdoor Unit Mounting (Ground, Wall Bracket, Rooftop)
• AC New Install — Condensate Drain Slope and Trap
• AC New Install — Outdoor Unit Clearance and Airflow Space
• AC Weak Cooling — Comprehensive Diagnosis (Filter, Coil, Refrigerant, Airflow)
• AC Completely Inoperative — Power, Breaker, Compressor, PCB Diagnosis
• AC Weak Cooling — Filter Clog (Most Common Cause)
• AC New Install — Refrigerant Line Routing (Bending, Traps, Oil Return)
• AC New Install — Line Set Length and Height Limit (Manufacturer Manual)
• AC New Install — Commissioning Checklist (ENERGY STAR / Korean KS)
• AC New Install — Pre-Charge / Purge / Service Valve Opening
• AC Intermittent Cooling — Repeated Auto ON/OFF (Short Cycling)
• AC Cooling Fault — Electronic Expansion Valve (EEV) Failure
• AC Weak Cooling — Outdoor Fan Stopped / Slow Speed
• AC Stops Immediately After Start — Protection Circuit Trip
• AC — Uneven Cooling Left/Right or Floor-by-Floor
• AC — Warm Air from Discharge / No Cooling Function
• AC Cooling Fault — Non-Condensable Gas (Air/Moisture) Contamination
• AC Indoor Coil Frost — Insufficient Airflow / Undercharge
• AC Weak Cooling — Outdoor Condenser Coil Fouling
• AC Indoor Unit Water Drip — Condensate Leak Diagnosis
• AC Drain Pump Fault — Forced Condensate Discharge Failure
• AC Drain Pipe Clog — Slime / Debris Removal
• AC Condensate Overflow — Auxiliary Pan or Ceiling Leak
• AC Outdoor Unit Leak — Condensation, Rain, or Drain Hose Failure
• AC Drain Pipe Freeze — Winter Drainage Failure
• AC Drain Trap Issue — Negative Pressure Loss / Odor Backflow
• AC Drain / Refrigerant Pipe Sweating — Inadequate Insulation
• AC PCB (Main Board) Fault — Diagnosis and Replacement
• AC Temperature Sensor (Thermistor) Failure
• AC Communication Error — Indoor/Outdoor Signal Failure (E-code)
• AC Remote Control No Response — Battery, IR, Signal Diagnosis
• AC Inverter Trip — Current / Temperature Protection
• AC Pressure Sensor (High/Low) Fault
• AC Compressor Overload — Thermal / Current Protection
• AC Capacitor Fault — Start / Run Capacitor Diagnosis
• AC Relay Fault — Contact Wear / Coil Open
• AC Indoor Unit Noise / Vibration — Blower, Blade, Cabinet Check
• AC Outdoor Noise / Vibration — Top Cause of Neighbor Complaints
• AC Compressor Knock / Metallic Sound — Liquid Slug / Mechanical Fault
• AC Fan Imbalance — Vibration / Noise on Rotation
• AC Refrigerant Flow Noise — Shhh / Hiss / Water-Like Sound
• AC Blower Belt Noise — Package / Ducted Systems
• AC Evaporator Frost/Defrost 'Pop' Sound
• AC Refrigerant Recovery Procedure (EPA 608 / Korean MOE Certified)
• AC R-32 Leak Response — A2L Safety Procedure
• R-22 System Retrofit to R-407C / R-422D Alternatives
• R-454B Transition — Next-Gen R-410A Replacement
• VRF Branch Pipe Design — Equivalent Length and Pipe Sizing
• VRF Y-Joint Installation — Horizontal / Inclination Rules
• VRF BS Box (Simultaneous Heat/Cool) Fault
• VRF Additional Refrigerant Charging — g/m by Pipe Length
• Package/Ducted Heat Exchanger Cleaning — Efficiency Restoration
• Duct Leak Test — Duct Blaster / Anemometer
• Package Coil Fin Corrosion — Coastal/Industrial Aluminum Damage
• Precision AC Humidifier Fault — IR, Steam, Spray Types
• Precision AC — Server Room N+1 / N+2 Failover System
• Precision AC Dehumid-Only Mode — Reheat / Response Time
• AC Cooling Season Pre-Start Check — Mandatory Items
• Heat Pump Heating Season Check — Defrost, Outdoor Condensate, Heat Trace
• AC Annual Leak Check — F-Gas Regulation Compliance
• AC Warranty / Maintenance Record — Digital Logging Required
• AC Compressor Lockout — Inverter Won't Start (LG CH21 / Samsung E311)
• Heat Pump 4-Way Valve Stuck — Mode Switch Fails (Samsung E311–E320)
• Field Purge Procedure — Tech Practice (Shortcut vs Vacuum Standard)
• Outdoor Unit Vibration / Noise Emergency — Case Tapping, Pads, Cable Ties
• LG AC CH Error Code Master — CH01–CH07 Field Diagnosis
• Samsung AC E/C Error Code Master — E101/E102/E121/E122/E151/E152
• EEV Stepping Motor Diagnosis — Coil Resistance, Back-EMF, Signal Check
• Comm Line L/N Swapped — #1 Cause of Communication Faults
• PCB Inverter Board Burn-out — Capacitor / IPM / Driver Fault
• NTC Temp Sensor Diagnosis & Replacement — 10kΩ @25°C + B-Constant Match
• Megger Insulation Resistance Test — Compressor / Motor / Breaker Safety
• Outdoor Fan Motor Bearing Replacement — Grinding Sound / Rotational Friction
• System AC Drain Pump Cleaning / Replacement — Ceiling Leak Emergency
• AC Pre-Season Checkup — 11-Item Tech Standard Checklist
• Standard Vacuum Procedure — −100.7 kPa (5 torr), 2.5h Pump, 1h Hold
• Capacitor μF Measurement — LCR Meter / Multimeter Capacitance Mode
• Evaporator Frost Diagnosis — 4 Causes (Undercharge / Overcharge / Airflow / Compressor)
• Refrigerant Leak Detection — Soap Bubble / Electronic / Tracer Gas / UV Dye
• R-32 Leak Safety Response — A2L Flammability Emergency Procedure
• AC Commissioning Report / Handover — Standard Form + Photos / Measurements
• Electrical Work Safety — LOTO (Lockout/Tagout) + Insulation PPE
• Flare Leak Emergency Fix — Cut, Re-Flare, Torque
• Refrigerant Mixing Prohibited — R-22 / R-410A / R-32 / R-454B Compatibility
• Coil Cleaning Chemical Safety — Neutral / Alkaline / Acidic Selection
• AC Warranty Claim Process — Coverage / Exclusions / Evidence
• AC Pre-Installation Site Survey — 8-Item Checklist + Quote
• PCB Killed by Lightning/Surge — SPD Install & Protection
• Post-Install Commissioning — 10-min Run, Pressure, ΔT Check
• AC Capacity Shortage — Install vs Leak vs Coil Blockage Diagnosis
• Outdoor Unit Sun Shielding — Efficiency & Compressor Protection
• Inverter vs Fixed-Speed — Diagnosis Priority Differences
• Refrigerant Recovery — No Venting, Use Recovery Machine
• 3-Phase Wiring Reversal — Compressor Rotation Check
• User Self-Check Card — 5 Steps Before Service Call
• VRF/Multi System — One Indoor Not Working (Addressing/Comm)
• Condensate Pump Noise & Failure — Vibration/Backflow/Diagnosis
• Flare vs Brazing — Field Selection Criteria
• Bird Nest / Wasp Nest in Outdoor Unit — Safe Removal & Prevention
• Outdoor Cabinet Resonance — Low-Speed Vibration/Noise Fix
• Handling Elderly Customers — Explanation/Demo/Paperwork
• Night/Quiet Mode Malfunction — User Reports & Diagnosis
• Rooftop Install Safety — Harness/Anchor/Fall Prevention
• Pipe Length Extra Charge — g/m Calc Beyond 7m
• Indoor Unit Water Leak — 5 Causes (Drain/Level/Insulation)
• BLDC Fan Motor Replacement — Inverter Outdoor Precision Diagnosis
• AC Tech Essential 30 Tools + Price Guide
• Receipt & Tax Invoice — Sole Proprietor Procedure
• Customer Complaint Script — 5-Step Dispute Prevention
• Self-Install vs Manufacturer Warranty — Dispute Avoidance
• R-32 Charging Procedure — A2L Safety, Ventilation, Ignition Source
• Condenser/Evaporator Fin Straightening — Comb & Compressed Air
• Indoor Mold/Smell Removal — Chemical Clean + UV-C Sanitize
• Setpoint ≠ Actual Temp — Control Algorithm Explained
• Window vs Split AC — Selection for Older Korean Homes
• 5 Power-Saving Myths — Customer Response
• Tropical Night Operation Strategy — When 25°C+ Disrupts Sleep
• Extreme Cold Defrost — Outdoor Heating Mode <-15°C
• R-22 Legacy Systems — Repair vs Replace Decision
• Sizing AC BTU by Room — Measure + Correction Factors
• Install Handover — 15-Photo Checklist
• On-Site Energy Audit — Current/Power/Run-Time Measurement
• Extended Warranty & Maintenance Package — Tech Revenue Model
• LG ThinQ / Samsung SmartThings Diag Mode — Remote 1st Diagnosis
• System Replacement Timing — 10-yr vs 15-yr Decision
• Cleaning Tool Sanitation — Prevent Cross-House Mold Transfer
• Water Hammer / Flare Leak — Vibration & Pulsating Pressure
• Multi-Split Load Balancing — 4+ Indoor Unit Optimization
• Pre-Season Marketing — Apr-May Booking Campaign
• Ceiling Cassette Install — Shops/Offices 4-Way Airflow
• Pet Household — Filter Management, Shorter Cleaning Cycle
• R-134a refrigerant handling — medium-temp & automotive (A1)
• R-290 (propane) handling — flammable A3 safety rules
• Compressor oil overcharge — slugging & compressor damage
• Walk-in cooler/freezer — not-cooling diagnosis
• Cascade system: high stage runs but low stage does not start (no cooling at all)
• Cascade unit will not reach -80°C, holds at -50 to -60°C
• Cascade unit: low running pressures on both sides (no cooling) — how to confirm a leak
• Two-stage compressor discharge gas temperature too high (oil carbonisation, viscosity loss)