1. Problem description and scope
This guide addresses the systematic diagnosis of loss of cooling capacity in chillers, heat exchangers and industrial refrigeration systems. Symptoms include elevated process temperatures, increased cycle time, high condensing pressure or low suction pressure alarms. This procedure applies to vapor compression chillers, chilled water systems and cooling towers. Classification: Critical if the process is continuous; Higher if it affects productivity.
SAFETY WARNING
Diagnosis of refrigeration systems involves electrical, mechanical and chemical risks. Before starting any inspection:
1. Apply Lockout Tagout (LOTO) procedures on the main power source before opening electrical panels.
2. Use appropriate PPE: safety glasses, chemical resistant gloves and safety shoes.
3. Contact with refrigerants can cause freeze burns. Never bleed coolant directly to the atmosphere.
4. Make sure there is no energy stored in capacitors or pressurized systems.
2. Diagnostic tools required
| Tool | Specification/Model | Measurement range | Purpose |
|---|---|---|---|
| digital multimeter | RMS, Fluke or similar | Up to 1000V AC/DC, 10A | Check motor voltages and currents |
| thermal imaging camera | Min resolution 160x120 | -20°C to +150°C | Detect hot spots in connections and obstructions |
| Ultrasonic flowmeter | Portable, clamp type | 0.1 to 10m/s | Measure real flow in pipes without cutting |
| Refrigeration pressure gauges | Analog/digital manifold | -1 to 30 bar | Check high and low pressures |
| vibration analyzer | Piezoelectric accelerometer | 10Hz to 10kHz | Evaluate mechanical health of compressors/pumps |
3. Initial checklist (Before diagnosing)
| Element | Action | Reference value |
|---|---|---|
| Suction pressure | Record pressure (bar) | See coolant P/T table |
| discharge pressure | Record pressure (bar) | Depends on ambient/water temperature |
| Process flow | Measure flow (m3/h or l/min) | Compare with nominal design |
| ΔT process water | Measure input and output | 5°C to 7°C nominal |
| Electrical consumption | Measure compressor amperage | Compare with nameplate |
4. Diagnostic flow chart
- Is the process fluid flow rate adequate?
- YES: Go to step 3.
- NO: Check line filter, partially closed valves or pump failure. Correct and verify.
- Is the temperature difference (ΔT) in the exchanger correct?
- YES: The physical system is correct; investigate external thermal load.
- NO: Suspect fouling or insufficient heat exchange.
- Are cooling pressures within design limits?
- Low Suction Pressure + High Superheat: Possible leak or restriction.
- High Suction Pressure + Low Subcooling: Inefficient compressor or excessive thermal load.
5. Matrix of failures and causes
| Symptom | Probable Causes (Ordered) | Diagnostic Test | Expected Result (Confirmed Cause) |
|---|---|---|---|
| High Temp. Process | Fouling, High thermal load, Low flow | Measure ΔT and flow | ΔT low + normal flow = Fouling |
| Low Pressure Suction | Refrigerant leak, Filter restriction, Low charge | Measure superheat | High superheat (>10K) = Lack of coolant |
| High Pressure Discharge | Dirty condenser, Air in system, Overload ref. | Cleaning/purging | Low pressure after cleaning = Dirty condenser |
6. Root cause analysis
Fouling: Accumulation of mineral scale or biofilm on the water side of the heat exchanger. Dramatically reduces the heat transfer coefficient. It is confirmed by an approach temperature greater than 3°C.
Low flow: Caused by worn pumps or clogged filters. It results in an abnormally high ΔT (>10°C) on the process side, as the fluid remains longer in the exchanger.
Inadequate refrigerant charge: A low charge reduces evaporation capacity. It is detected with low suction pressures and excessive superheat (measured at the compressor suction).
7. Step-by-step resolution procedures
- Cleaning of exchangers: Perform chemical cleaning (CIP) using mild (inhibited) acids or mechanical cleaning if the design allows it. Check pressures before and after.
- Refrigerant charge adjustment: Use precision scale. Recover, vacuum (<500 microns) and load by weight according to plate.
- Flow optimization: Clean filters (Y-strainers), verify pump alignment and review performance curves against the operating point.
8. Preventive measures
| Root Cause | Prevention Strategy | Monitoring | Interval |
|---|---|---|---|
| Fouling | Chemical water treatment | Water quality analysis | Monthly |
| Coolant leaks | Visual inspection/detector | Pressure analysis | Quarterly |
| Low flow | Preventive filter change | difference pressure gauges | Semester |
9. Spare parts and components
| Component Description | Specification | When to replace | UNITEC Category |
|---|---|---|---|
| Filter drier | Threaded/weld type | After system opening or every 2 years | Filters-HVAC |
| circulation pump | Centrifuge, Q=XX m3/h | According to vibration analysis (>6 mm/s) | Pumps-Hydraulics |
| Temperature sensors | PT100/NTC | If the deviation exceeds 1°C | Sensors-Control |
| Expansion valve | Thermostatic/Electronic | If it does not regulate overheating | Valves-Regulation |
To obtain original and compatible spare parts, visit our e-catalog: https://www.unitecd.com/e-catalog/
10. References
- UNE-EN 378: Refrigeration systems and heat pumps.
- ISO 10816: Evaluation of mechanical vibrations.
- OEM service manuals for industrial chillers.
