Preventive maintenance means reading the operating trends and fixing the cause before the chiller trips on high pressure or stops the production line. A chiller that is only repaired after it breaks down wears out its compressor sooner and uses more electricity all year. This is a practical plan for technical managers and operators, from the daily log sheet to the annual service. If you are still choosing a chiller, start with the buying guide.
The five actions with the biggest effect
- Log the readings every day: supply and return water temperature, suction and discharge pressure, compressor current, superheat and condenser approach.
- Keep heat transfer surfaces clean: scale and dust lower heat transfer, raise condensing pressure and increase power use.
- Protect the compressor: treat falling oil level as a symptom and find the cause; topping up alone is not enough.
- Control superheat and freeze protection: expansion valve setting, flow switch and glycol concentration.
- Service on a schedule: follow a plan and the compressor manufacturer's instructions, not only after a fault.
The daily log sheet: your first early-warning tool
A simple daily log is the cheapest diagnostic tool there is. Record these values at the same time each day:
- Evaporator entering and leaving water temperature
- Condenser entering and leaving water temperature (water-cooled units)
- Suction and discharge pressure and the matching saturation temperatures
- Superheat and subcooling
- Current of each compressor and the oil level
- Pressure drop across the water strainer and the filter drier
The key indicator is the condenser approach: the difference between the condensing temperature and the water (or air) leaving the condenser. A slow rise means fouling. The reason is in the heat transfer equation Q = U · A · ΔTlm with 1/U = 1/Uclean + Rf: scale increases the fouling resistance Rf and lowers U, so the temperature difference has to grow to move the same heat. Condensing pressure rises, the compressor works harder and COP falls. Without a log, this loss stays hidden for months.
Service schedule
| Interval | Tasks |
|---|---|
| Daily | Log sheet readings, listen for unusual noise, check for alarms |
| Monthly | Clean strainers, inspect the condenser coil or tower, check fans and belts, look for oil traces (leaks) |
| Quarterly | Check electrical connections and contactors, test the flow switch and safety switches, check glycol concentration |
| Before summer | Clean the condenser coil or tower thoroughly, make sure the air path is clear |
| Annually | Full service: heat exchanger cleaning, leak test, filter drier check, controller and sensor calibration |
This is a general plan. For each unit, the compressor manufacturer's instructions and the operating conditions (continuous duty, dust, water quality) decide the final intervals.
Cleaning the condenser and evaporator correctly
The right method depends on the heat exchanger, and the wrong one can damage the machine.
- Shell-and-tube condenser (water-cooled): brush the tubes mechanically or clean them with an acid solution containing a corrosion inhibitor. How often depends on the hardness of the tower water.
- Shell-and-tube evaporator: usually on a closed loop with less scale. Use controlled chemical cleaning; never use a high-pressure water jet on the tubes.
- Air-cooled condenser coil: switch off the power first, then wash with water or low-pressure compressed air against the direction of air flow, taking care not to bend the fins.
Much of the scale can be prevented by controlling water quality. See shell-and-tube heat exchangers and cooling towers.
Compressor and oil: find the cause, do not just add oil
In scroll and screw compressors, the oil lubricates and also carries heat and wear particles away from moving parts. A falling oil level usually has one of these causes: a leak, poor oil return to the compressor, low superheat or liquid refrigerant returning. Adding oil without fixing the cause does not solve the problem, and too much oil can make it worse.
- Read the oil level in the sight glass with the chiller running and stable.
- On semi-hermetic compressors, regular oil analysis (acidity, metal particles) and vibration monitoring reveal wear before you can hear it.
- Use only the oil type and grade specified by the compressor manufacturer and never mix oils.
Superheat and freeze protection
The expansion valve controls superheat. Too little superheat risks liquid returning to the compressor; too much reduces capacity. The target is usually a few kelvin; set it according to the manufacturer's datasheet.
- Flow switch: loss of chilled water flow is the fastest way to freeze an evaporator. Test the switch regularly.
- Leaving water set point: without glycol, do not set the leaving water temperature close to 0 °C.
- Glycol: for temperatures below the range of plain water, measure the glycol concentration with a refractometer.
Frequent fault codes and fixes are in common chiller faults and error codes.
Air and moisture in the refrigerant circuit
Air (non-condensable gas) in the circuit raises condensing pressure without any real increase in load. Moisture combines with refrigerant and oil to form acid. Warning signs: discharge pressure too high for the condenser water temperature, the moisture indicator on the filter drier showing wet, and darkening oil. The fix is a leak test, evacuation with a vacuum pump during service and a new filter drier, carried out by a qualified technician.
Water flow and ΔT
Water flow must match the design capacity and temperature difference: Q = ṁ · cp · ΔT. For example, 100 kW with a 5 K ΔT needs about 17 m³/h of water (cp of water ≈ 4.18 kJ/kg·K). In imperial units, flow per ton of refrigeration is about 24 ÷ ΔT (°F) US gallons per minute. Too little flow lowers the evaporator temperature and increases the freezing risk; too much raises pump power and tube erosion. Variable speed drives on pumps and fans are a common way to save energy at part load.
Seasonal care
In summer the main risk is high condensing pressure and high-pressure trips: before the hot season, clean the coil or tower, check the fans and make sure the air path is free. In winter the main risk is water freezing in the pipes and the evaporator: drain unused circuits or protect them with glycol and trace heating.
What to leave to a qualified technician
Operators can log readings, clean the outside of the coil and inspect visually. Refrigerant charging and recovery, replacing refrigerant circuit parts, adjusting the expansion valve and controller parameters, work on the power panel and compressor repairs belong to a qualified technician. Mistakes here are a safety risk and can void the warranty.
Frequently asked questions
How often should an industrial chiller be serviced?
Readings daily, inspections monthly and quarterly, a full service once a year, plus a check before summer. Continuous duty or a dusty site needs shorter intervals; the manufacturer's instructions are the final reference.
What are the first signs that service is needed?
Rising compressor current, rising discharge pressure or condenser approach, leaving water temperature drifting, unusual compressor noise or vibration, and repeated controller alarms.
Can we service the chiller ourselves?
Logging and external cleaning, yes. Work on the refrigerant circuit, the electrical panel and the compressor should be done by a qualified technician.
How do I choose a reliable service company?
Check experience with your compressor brand, proper measuring equipment, a written report after each visit, access to spare parts and a warranty on the work.
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