1. Problem Description and Scope
This guide addresses the diagnosis of loss of capacity in industrial refrigeration systems (chillers, condensing units, direct expansion systems). Common symptoms include process temperature above the setpoint, compressor operating in a continuous cycle (100% duty cycle), frequent activation of high discharge pressure or low suction pressure alarms, and high energy consumption without a corresponding increase in load.
The severity of this failure is classified as critical, as it can result in production stoppage, raw material deterioration or permanent damage to the compressor due to overheating or liquid backflow.
2. Safety Precautions
WARNING: Maintenance operations on refrigeration systems involve risks of high voltage, high pressures and dangerous chemical fluids. It is mandatory to use full PPE: safety glasses, chemical-resistant thermal gloves and protective boots. Always perform lockout and tagout (LOTO - Lockout/Tagout) of power sources before removing any panel or carrying out mechanical intervention. Operating pressures can exceed 25 bar; handle hoses with extreme caution.
3. Required Diagnostic Tools
| Tool | Specification/Model | Measuring Range | Purpose |
|---|---|---|---|
| Digital Manifold | Accuracy ±0.5% | -1 to 50 bar | Measure suction and discharge pressures, calculate superheat/subcooling. |
| True RMS Multimeter | Class CAT III 600V | 0-600V / 0-100A | Check voltage, current of the compressor and fans. |
| Thermographic Camera | Minimum thermal resolution 160x120 | -20°C to 300°C | Identify areas of high electrical resistance or thermal exchange failures. |
| Ultrasonic Flow Meter | Clamp-on type | 0.1 to 10 m/s | Check the secondary fluid flow (water/glycol) in the evaporator and condenser. |
4. Initial Assessment Checklist
| Verification | Observation Required |
|---|---|
| Process setpoint | Record current value vs. nominal value. |
| suction pressure | Compare with the fluid saturation table for the load regime. |
| Discharge pressure | Check if it is within the manufacturer's curve. |
| Current (Amperage) | Check for unbalance between phases or current above nominal (FLA). |
| Alarm history | Identify recurrence of high/low pressure switch. |
| Ambient temperature | Record dry bulb temperature at the condenser inlet. |
5. Systematic Diagnosis Flow
- Check Compressor Condition: Does the compressor operate?
- NO: Check control failures, safety pressure switch, contactor.
- YES: Go to step 2.
- Pressure Analysis:
- Low Suction + Low Discharge: Probable restriction in the filter drier or lack of fluid (leak).
- Low Suction + Normal/High Discharge: Possible fouling in the evaporator or insufficient thermal load flow.
- High Suction + Low Discharge: Compressor with low compression (internal damage to the valves).
- High Suction + High Discharge: Clogged condenser, excess fluid or non-condensables in the system.
- Check Thermal Exchange:
- Measure Delta-T at the inlet and outlet of the evaporator and condenser. If Delta-T is well below design, check for fouling or lack of secondary fluid flow.
6. Failure-Cause Matrix
| Symptom | Probable Cause | Diagnostic Test | Expected result (if cause confirmed) |
|---|---|---|---|
| Low suction, normal discharge | Fouling in the evaporator | Measure Delta-T (water) | Very low Delta-T |
| High suction, high discharge | Condenser obstruction | Visual inspection/Thermography | High thermal gradient on the surface |
| Low capacity, low current | Lack of refrigerant | Superheat | Overheating above 12K |
| Low capacity, high current | Excess fluid or incondensables | Subcooling | Very low or high subcooling |
7. Root Cause Analysis
7.1 Fouling
The accumulation of salts, sediments or biofilm on the internal surfaces of exchangers creates thermal resistance (fouling factor) that prevents efficient heat transfer. Confirmation: Measurement of pressure drop (differential pressure) in the exchangers greater than that specified by the manufacturer.
7.2 Incorrect Refrigerant Charge
Leaks reduce the mass of circulating fluid, reducing the heat extraction capacity. Excess refrigerant increases the discharge pressure, forcing the compressor. Confirmation: Rigorous calculation of superheating (at the compressor suction) and subcooling (at the condenser outlet).
8. Resolution Procedures
- Chemical Cleaning of Exchangers:
- Isolate the exchanger.
- Use an external circulation pump with a specific cleaning solution depending on the exchanger material (copper/stainless steel).
- Neutralize the system and wash with clean water.
- Check pressure drop after cleaning.
9. Preventive Measures
| Cause | Prevention Strategy | Monitoring | Interval |
|---|---|---|---|
| Fouling | Chemical water treatment | Conductivity analysis | Weekly |
| Fluid Loss | Tightness test | Leak sensor | Monthly |
10. Spare Parts and Components
| Description | Specification | When to Replace | UNITEC category |
|---|---|---|---|
| Filter Dryer | liquid line | Always after opening the system | Maintenance |
| Refrigerant Fluid | As per board specification | After leak correction | Consumable |
For original parts and detailed technical manuals, visit: https://www.unitecd.com/e-catalog/
11. References
- ABNT NBR 16401: Air conditioning installations - Central and unitary systems.
- NR-10: Safety in electrical installations and services.
- NR-12: Work safety on machines and equipment.
- OEM manuals for compressors and heat exchangers.
