Industrial chillers serve as the core power equipment in refrigeration systems, widely applied in chemical, pharmaceutical, food processing, data center, and HVAC sectors. Their operating state directly determines production process temperature precision, operational continuity, and energy efficiency. A well-maintained chiller unit operates with high efficiency, low energy consumption, and an extended lifespan of 30%-50%. Conversely, lack of maintenance leads to capacity decay, frequent compressor failures, and soaring power bills. This article provides a comprehensive, practical guide across six critical dimensions.

Ⅰ. Daily Operational Inspection: Establishing Preventive Maintenance

1. Operating Parameter Logging & Trend Monitoring 

Log core operating parameters at least once per shift: suction/discharge pressure and temperature, chilled water in/out temperatures and flow, cooling water in/out temperatures, compressor current, oil level, and oil temperature. The key lies in long-term trend changes. A monthly rise in discharge pressure indicates condenser scaling; dropping suction pressure signals leakage or expansion valve abnormality; dropping oil level indicates system oil carryover.

2. Visual & Sensory Inspection 

Conduct daily inspections using "Look, Listen, Touch": 

•  Look: Check pipe joints, valves, and sight glasses for oil stains (oil stain = refrigerant leak); verify compressor oil level is within 1/3-2/3; check condenser fins for clogging.
•  Listen: Ensure smooth compressor operation without abnormal knockings (liquid slugging); verify expansion valves exhibit steady throttling sounds. 
• Touch: Compressor suction line should feel cool, discharge line warm/hot (not burning hot); check for normal temperature drops across heat exchangers.

3. Periodic Testing of Safety Devices 

Test high/low pressure switches, oil differential pressure switches, water flow switches, and temperature cut-outs monthly. Inactive protection devices can fail over time due to contact oxidation or spring fatigue.

Ⅱ. Periodic Maintenance of Key Components

1. Compressor Maintenance 

•  Refrigerant Oil Management: Inspect oil quarterly. Dark or burnt-smelling oil indicates carbonization and must be replaced immediately. Replace oil and oil filters at least once a year (every 6 months for heavy-duty applications). 
•  Motor Insulation Testing: Measure motor winding insulation resistance semi-annually using a megohmmeter (standard: ≥50 MΩ). 
• Vibration & Shaft Seal Inspection: Check mechanical shaft seals for oil leakage quarterly and measure vibration levels (generally ≤7.1 mm/s).

2. Condenser Maintenance 

Scale thermal conductivity is extremely low. A 0.8mm scale layer reduces heat transfer efficiency by ~7%, while 3.2mm reduces efficiency by ~18%, leading to high discharge pressure and excessive power consumption. 

• Air-Cooled Condensers: Clean dust monthly using compressed air (≤0.4 MPa) or soft brushes. Clean stubborn grease quarterly with special fin cleaners. Never use high-pressure water jets as they bend the fins. 
•  Water-Cooled Condensers: Inspect water quality and in/out temperature difference quarterly (normal: 4-6°C). Perform mechanical tube cleaning (bullet cleaning/brushing) at least once a year to remove scale and bio-slime.

3. Evaporator Maintenance 

• Flow Rate Assurance: Clean Y-strainers monthly and verify water flow switch responsiveness to prevent evaporator starving or compressor liquid slugging. 
•  Anti-Freeze Protection: In winter or shutdown periods below 0°C, drain all water from evaporators and piping, or keep chilled pumps circulating with electric anti-freeze heaters active. Evaporator freeze-cracking causes severe financial loss.

Ⅲ.  Water Quality Control: Maintaining the "Blood" of the System

1. Cooling Water Control (Open Loop) 

•  Cycles of Concentration (CoC): Maintain CoC between 2-4 through controlled blowdown (conductivity ≤4000 μS/cm). High CoC forms calcium scale; low CoC wastes water and chemicals. 
•  Chemical Dosing: Add corrosion/scale inhibitors and biocide. Alternate between oxidizing and non-oxidizing biocides weekly during summer to prevent bacterial resistance. 
• Control Parameters: pH 7.0-9.0, Total Hardness ≤800 mg/L (as CaCO₃), Chloride ≤700 mg/L (stainless steel exchanger).

2. Chilled Water Control (Closed Loop)

 Use softened or purified water for makeup. Maintain pH between 8.0-9.5 to inhibit carbon steel corrosion. Test water samples annually.

Ⅳ. Refrigerant & System Sealing Management

1. Leak Detection 

"Oil stains mean leaks". Focus inspections on shaft seals, pipe joints, flanges, and valve stems. Confirm suspect areas with electronic leak detectors or soap bubble solutions.

2. Operating Parameter Indicators 

Continuous bubbles in the sight glass during full load indicate low refrigerant or moisture presence. Low subcooling (normal: 4-8°C) and high superheat also signal refrigerant shortage.

3. Pressure Testing & Charging 

Perform a system pressure test annually with dry nitrogen for 24 hours (pressure drop should not exceed 1%). Always charge refrigerant incrementally while monitoring superheat, subcooling, and sight glass indicators to avoid overcharging.

Ⅴ. Electrical and Control System Maintenance

1. Electrical Cabinet & Wiring 

Re-tighten all terminal screws quarterly (loose terminals cause phase loss and electrical fires). Perform infrared thermography to check for hot spots (terminals should not exceed ambient temperature by >30°C). Clear cabinet dust.

2. Control Systems 

Check PLC memory battery voltage monthly. Calibrate temperature sensors and pressure transmitters annually against standard instruments.

3. Pumps & Motors Measure 

pump motor insulation semi-annually. Replace pump mechanical seals every 8,000-10,000 operating hours or upon leakage.

Ⅵ. Seasonal Operation & Shutdown Maintenance

1. Pre-Start Checks 

Perform leak tests, electrical insulation checks, valve positioning, pump rotation checks, and cooling tower inspections before seasonal commissioning. Monitor parameters continuously for the first 30 minutes of operation.

2. Long-Term Shutdown Care 

For shutdowns exceeding 1 month: Drain all water from water-cooled condensers and piping. Keep crankcase heaters energized to prevent refrigerant migration into compressor oil. Close suction/discharge stop valves. Replace refrigerant oil prior to restarting.

Ⅶ. Maintenance Cycle Quick Reference Table

•  Daily / Shift: Log parameters; perform visual/audible/tactile checks; inspect sight glass. 
• Weekly: Test cooling water quality; check cooling tower float valves; check pipe joints for leaks. 
• Monthly: Test safety switches (HP/LP, flow switch); clean chilled water Y-strainers; clean air-cooled fins. 
•  Quarterly: Check compressor oil quality/color; tighten electrical terminals; check condenser temperature drop. 
• Semi-Annually: Measure motor insulation resistance; check evaporator water-side scaling; calibrate sensors; perform leak detection. 
• Annually: Replace compressor oil and oil filters; replace filter driers; perform condenser mechanical tube cleaning (bullet cleaning); execute 24h nitrogen pressure hold test.

Ⅷ. Conclusion

Chiller maintenance is a systematic preventive framework. Follow four principles:

1. Parameter-Driven: Long-term data trends reveal developing faults.
2. Water Quality First: Controlling water quality prevents the majority of condenser scaling and efficiency loss.
3. Periodic Execution: Stick strictly to maintenance schedules for oil replacement, tube cleaning, and terminal tightening.
4. Attention to Detail: Resolve minor leaks or loose wiring immediately before they evolve into major equipment breakdowns.