Troubleshooting Guide: Insufficient Capacity in Industrial Refrigeration Systems

1. Problem Description and Scope

Insufficient capacity in industrial refrigeration systems manifests itself when the equipment is unable to remove the thermal load necessary to maintain the process temperature within specified limits. This can lead to process failures, degradation of product quality and production losses. This guide covers the symptoms, diagnosis, and resolution of common causes associated with this condition.

Affected Equipment:

• Air or water chillers.
• Cooling Towers.
• Circulation pumps (chilled water, condensation water, process).
• Heat exchangers (evaporators, condensers, process exchangers).
• Expansion valves and other components of the refrigerant circuit.
• Piping and associated instrumentation.

Severity Rating:

• Critical: Process temperature exceeds operational limits, resulting in immediate production shutdown or imminent risk of equipment damage.
• Major: The process temperature is consistently above the setpoint, impacting efficiency, product quality or requiring operation under abnormal conditions (e.g. use of backup equipment, excessive energy consumption).
• Minor: Specific or gradual deviations in the process temperature, without immediate impact, but indicating degradation of performance and the need for preventive intervention.

2. Safety Precautions

ATTENTION: Before starting any diagnostic or maintenance procedure on refrigeration systems, it is CRITICAL to strictly follow the safety procedures of ABNT NBR 5410, NR-10 (Safety in Electrical Installations and Services) and NR-12 (Safety at Work in Machines and Equipment). Failure to follow these guidelines could result in serious injury or death.

• Lockout and Tagout (LOTO): Make sure that all energy sources (electrical, pneumatic, hydraulic) are de-energized and blocked before intervening in any component. Check the absence of voltage with appropriate equipment.
• Stored Energy: Refrigeration systems contain stored energy (refrigerant pressure, electrical capacitors, potential energy in suspended components). Depressurize the system carefully before opening any part of the refrigerant circuit. Discharge electrical capacitors.
• Personal Protective Equipment (PPE): Always use appropriate PPE: safety glasses or face shield, gloves resistant to chemicals and extreme temperatures, safety shoes and protective clothing. When handling refrigerants, a respiratory protection mask may be necessary.
• Refrigerants: Refrigerants can cause frostbite on skin contact and can displace oxygen in confined spaces. Work in well-ventilated areas. Avoid inhaling vapors.
• High Temperatures: Hot surfaces (condensers, compressors) can cause burns.
• High Pressures: Refrigerant circuits operate under high pressure. Never force connections or attempt improvised repairs on pressurized components.

3. Required Diagnostic Tools

The use of calibrated and specific tools is essential for an accurate diagnosis.

4. Initial Assessment Checklist

Before starting in-depth diagnosis, collect the following information for a preliminary view of the situation.

5. Systematic Diagnosis Flowchart

This flowchart guides the technician through a logical sequence to identify the root cause of insufficient capacity. Follow the steps in the order presented.

1. Initial Symptom: Process temperature above setpoint.
   1. Check Process Thermal Load:
      • Measure flow and inlet/outlet temperatures of the process fluid in the heat exchanger.
        • Measurement: Contact thermometer and flow meter.
        • Analysis: Compare with project values.
        • IF Current thermal load is SIGNIFICANTLY greater than design:
          1. Probable Cause: Process thermal overload.
          2. Action: Investigate additional heat sources in the process or operation outside design parameters.
             • IF Identified and corrected → Check system performance.
             • IF Not identified or corrected → Continue cooling system diagnosis.
        • IF Current heat load is WITHIN design limits:
          1. Action: Proceed to check refrigeration system.
   2. Check Chilled Water/Glycol Flow:
      • Measure the fluid flow in the chilled water circuit (evaporator).
        • Measurement: Ultrasonic flow meter on the evaporator inlet/outlet piping.
        • Analysis: Compare with the nominal flow rate of the chiller. (Ex: For a 100 TR chiller, typical flow of 1200 L/min).
        • IF Flow is BELOW 90% of nominal:
          1. Probable Cause: Low chilled water flow.
          2. Sub-diagnosis:
             • Check Chilled Water Pump:
               • Measure electrical current of the pump (Ammeter).
                 • IF Low current in relation to the nominal → Cause: Clogged rotor, closed discharge valve, low rotation.
               • Check pump suction and discharge pressure (Manometers).
                 • IF Low discharge pressure, normal suction → Cause: Worn pump or cavitation.
                 • IF Very low suction pressure (vacuum) → Cause: Obstruction in suction, isolation valve partially/fully closed, low level in the chilled water tank.
             • Check Isolation and Control Valves:
               • Visually inspect the position of the valves.
               • IF Valves not fully open or failed actuators → Cause: Flow restriction.
             • Check Y/Basket Filters:
               • Visually inspect or check pressure drop in the filter.
               • IF Pressure drop > 0.5 bar → Cause: Filter clogged.
             • Check Evaporator:
               • Measure pressure drop in the evaporator.
               • IF Pressure drop > 0.8 bar above nominal → Cause: Internal fouling in the evaporator (water side).
        • IF Flow is WITHIN design limits:
          1. Action: Proceed to check the quality of the thermal exchange.
   3. Check Thermal Exchange Efficiency (Evaporator and Condenser):
      • Check Evaporator (refrigerant side):
        • Measure superheat at the evaporator outlet.
          • Measurement: Digital manifold (suction pressure) and contact thermometer (suction line temperature).
          • Calculation: Suction line temperature - Saturation temperature corresponding to the suction pressure.
          • Expected Value: 5-8°C (depending on refrigerant and design).
          • IF Very HIGH superheat (> 10°C):
            1. Probable Cause: Low refrigerant charge or Thermostatic Expansion Valve (VET) underfeeding the evaporator.
            2. Action: Check refrigerant charge and VET operation.
          • IF Very LOW or NEGATIVE superheat (< 3°C):
            1. Probable Cause: VET overfeeding the evaporator (liquid returning to the compressor - risk of liquid shock) or overheating due to low thermal load (less likely for the symptom).
            2. Action: Adjust VET or check thermal load.
        • Measure pressure drop in the evaporator (refrigerant side).
          • Measurement: Digital manifold.
          • IF Significantly high pressure drop → Cause: Internal fouling in the evaporator (refrigerant side) or restrictive VET.
      • Check Condenser:
        • Measure subcooling at the condenser outlet.
          • Measurement: Digital manifold (discharge pressure) and contact thermometer (liquid line temperature).
          • Calculation: Saturation temperature corresponding to discharge pressure - Liquid line temperature.
          • Expected Value: 5-8°C (depending on refrigerant and design).
          • IF Very LOW subcooling (< 3°C):
            1. Probable Cause: Low refrigerant charge.
          • IF Very HIGH subcooling (> 10°C):
            1. Probable Cause: Excess refrigerant charge or restriction in the condenser/liquid line (e.g. clogged filter dryer).
        • Air Condenser:
          • Visually inspect the fins for obstruction (dirt, leaves, debris).
          • Measure the temperature of the inlet and outlet air. The difference must be consistent with the design.
          • Check the operation of the fans (current, rotation, noise).
          • IF Clogged fins or poorly performing fans → Cause: Poor thermal exchange.
        • Water Condenser (Cooling Tower):
          • Measure condensation water flow.
            • IF Flow below nominal → Investigate tower pump, valves, filters, fouling in pipes.
          • Check the inlet and outlet temperature of the condensation water in the condenser.
            • IF Very low or very high temperature difference in relation to the design → Indications of low flow or fouling.
          • Check for scale in the condenser pipes (water side).
            • Measure pressure drop in the condenser (water side).
            • IF Pressure drop > 0.5 bar above nominal → Cause: Fouling.
          • Check tower water parameters (pH 7.0-8.5, conductivity < 1500 µS/cm).
            • IF Out of range → Cause: Problems in water treatment, leading to scale or corrosion.
   4. Check Refrigerant Charge:
      • Use the electronic refrigerant scale to check the amount of refrigerant in the system.
        • Measurement: Collect and weigh the refrigerant, comparing it with the nominal load of the equipment.
        • Alternative (less accurate): Evaluate superheating and subcooling together.
        • IF Load significantly BELOW nominal (> 10% difference):
          1. Probable Cause: Refrigerant leak.
          2. Action: Locate and repair leak (electronic leak detector, soap suds), evacuate and recharge system.
        • IF Load significantly ABOVE nominal (> 5% difference):
          1. Probable Cause: Excess refrigerant charge.
          2. Action: Remove excess refrigerant.
        • IF Charge WITHIN nominal:
          1. Action: Rule out refrigerant charge as primary cause. Reevaluate other factors.

6. Failure and Cause Matrix

This matrix correlates observed symptoms with probable causes, diagnostic tests and expected results.

7. Root Cause Analysis for Each Failure

Understanding the why of failure is crucial to preventing recurrence.

7.1. Low Refrigerant Charge

Explanation: The amount of refrigerant in the system is below the design level, usually due to a leak. This reduces the mass of circulating refrigerant, reducing the heat absorption capacity in the evaporator and heat rejection capacity in the condenser. Consequently, superheating increases in the evaporator and subcooling decreases in the condenser.

Confirmation: Weigh the refrigerant charge and compare it with the nominal. Visual inspection and use of an electronic leak detector or foam/soap water solution on connections and welds to locate the leak point. Abnormal suction and discharge pressures (generally lower than expected). Subcooling less than 3°C.

Unresolved Damage: Inefficient operation, increased energy consumption. The compressor may overheat due to lack of refrigerant to cool the windings and bearings, leading to premature compressor failure.

7.2. Scaling/Fouling in Heat Exchangers (Evaporator/Condenser)

Explanation: Accumulation of dirt, minerals (limestone), algae, sludge or other deposits on the internal or external surfaces of heat exchangers. This creates a thermal barrier that prevents efficient heat transfer between the coolant/water and the process fluid/ambient air. In air condensers, dirty fins prevent air from passing through. In shell and tube (water) exchangers, fouling reduces the overall heat exchange coefficient and increases the pressure drop.

Confirmation:

• Air Condenser: Visual inspection of the fins. Measurement of inlet and outlet air temperature.
• Water Condenser/Evaporator: Measurement of the pressure drop across the exchanger (if significantly greater than the design value, it indicates internal obstruction). Analysis of water quality (pH, conductivity, suspended solids) to identify problems in water treatment. Disassembly and visual inspection of pipes.
• Thermographic Camera: Can reveal irregular temperature patterns on exchanger surfaces, indicating areas of fouling.

Unresolved Damage: Drastic decrease in efficiency, increase in discharge pressure (in the condenser), increase in process temperature. Suction pressure can drop (in the evaporator), increasing the compression ratio and overloading the compressor, resulting in early failure. Increased energy consumption to compensate for inefficiency.

7.3. Low Fluid Flow (Chilled Water, Condensation Water, Air)

Explanation: Inadequate flow of any of the working fluids (chilled water in the evaporator, condensation water in the water condenser, or air in the air condenser) limits the amount of heat that can be transferred. A failed pump, poorly positioned valves, clogged filters or poorly performing fans are common causes. Low chilled water flow reduces the heat absorption capacity of the evaporator, while low condensing water/air flow makes it difficult for the condenser to reject heat, both resulting in insufficient capacity.

Confirmation:

• Direct Flow Measurement: Use an ultrasonic flow meter for water, or anemometer for air (in air condensers).
• Pump Check: Measure electrical current, suction and discharge pressures. Vibration analysis.
• Fan Check: Measure current, rotation, inspect blades.
• Inspection of Filters and Valves: Visual inspection for obstructions in filters, position and operation of valves. Measure pressure drop across filters.

Unresolved Damage: Operational inefficiency, increase in process temperature. Low water flow in the evaporator can cause the evaporator to freeze, damaging the heat exchanger. In the condenser, low flow leads to high discharge pressure and compressor overheating.

7.4. Failed Thermostatic Expansion Valve (VET)

Explanation: The VET is responsible for controlling the refrigerant flow to the evaporator, maintaining adequate superheat at the outlet. A failed VET can underfeed (too little refrigerant) or overfeed (too much refrigerant) the evaporator.

• Undersupply: Sensor bulb with loss of charge, incorrect adjustment, orifice partially blocked. Causes excessive overheating and low suction pressure.
• Overpower: Sensor bulb poorly positioned or with poor insulation, incorrect adjustment, orifice excessively open. Causes very low or negative superheat, with risk of liquid hitting the compressor.

Confirmation: Accurate superheat measurement. Inspection of the sensor bulb (position, contact, insulation). Checking the VET adjustment (if adjustable). Use a thermometer to compare the suction line temperature with the saturation temperature at the suction pressure. A differential that is too high or too low indicates failure.

Unresolved Damages: Inefficiency. Underfeeding causes loss of capacity. Overcharging can lead to liquid shock and severe damage to the compressor (valves, pistons, bearings).

7.5. Non-Condensable Gas in the System

Explanation: The presence of gases such as air, nitrogen or moisture (which vaporizes) in the refrigerant system. These gases do not condense under the condenser's operating conditions, taking up space that should be the refrigerant, increasing the discharge pressure and condensation temperature without contributing to the refrigeration capacity.

Confirmation: Measure the discharge pressure and the temperature of the saturated liquid at the condenser outlet. If the liquid temperature is significantly below the saturation temperature corresponding to the discharge pressure, or if the discharge pressure is abnormally high for the ambient temperature, non-condensables are likely present. Refrigerant analysis can confirm.

Unresolved Damage: Extreme increase in discharge pressure, compressor overload, increase in compressor discharge temperature, risk of activation of high pressure switches, reduction in compressor useful life and increased energy consumption.

8. Step-by-Step Resolution Procedures

Always perform Lockout and Tagout (LOTO) and use appropriate PPE before beginning any repair. ATTENTION: HANDLING REFRIGERANTS REQUIRES CERTIFIED PROFESSIONALS.

8.1. Resolution for Low Refrigerant Charge (Leak)

1. SAFETY: Lockout and Tagout (LOTO) of the chiller. Use full PPE.
2. Locate Leak: Use an electronic leak detector and/or foam/water and soap solution on all connections, welds, seals and piping in the system. Pay special attention to valves, sight glasses, flanged joints and where there is vibration.
3. Repair Leak: After locating, isolate the affected section (if possible). Collect the remaining refrigerant into a recovery cylinder. Carry out the repair (welding, gasket/sealing ring replacement, retightening).
4. Tightness Test (Pressurization): Pressurize the repaired section (or the complete system if necessary) with Dry Nitrogen (N2) at 10-15 bar. Check leaks again with detector. Maintain the pressure for at least 24 hours (ABNT NBR 16655).
5. Evacuation: Connect the vacuum pump and evacuate the system until a deep vacuum of 250 microns (approximately 0.33 mbar) is reached, maintaining this vacuum for 30 minutes after isolating the pump. This removes moisture and non-condensables.
6. Refrigerant Recharge: With the system in vacuum, charge the refrigerant in the liquid phase using the electronic scale. Load the exact amount specified by the manufacturer. For R-410A, always charge in the liquid phase.
7. Post-Repair Check: Turn on the system, monitor pressures (suction/discharge), temperatures (superheat, subcooling), and overall performance to ensure capacity has been restored.

8.2. Resolution for Fouling/Fouling in Heat Exchangers

1. SECURITY: Locking and Tagging (LOTO). Wear chemical-appropriate PPE (if applicable).
2. Air Condenser:
   • External Cleaning: Turn off fans and compressor. Use compressed air or a low-pressure water jet with specific fin descaling detergent. Rinse thoroughly. Make sure the fins are not damaged.
3. Water Condenser/Evaporator (Shell and Tubes):
   • Chemical Cleaning (CIP - Cleaning In Place): Isolate the exchanger from the main circuit. Circulate an acidic (for mineral scale) or alkaline (for organic deposits/sludge) cleaning solution, as recommended by the chemical and exchanger manufacturer. Monitor pH and temperature of the solution.
   • Mechanical Cleaning (if detachable): Remove the exchanger covers. Use specific brushes or high pressure water blasting to remove internal deposits from the pipes. Inspect pipes for corrosion or erosion.
   • Rinse: After cleaning, rinse the exchanger completely until the pH of the leaving water is neutral.
4. Post-Clean Scan: Restore the system. Measure the pressure drop across the exchanger again and compare with the design values. The pressure drop should return to normal levels. Monitor overall chiller performance.

8.3. Resolution for Low Fluid Flow

1. SAFETY: Locking and Tagging (LOTO) of the pump/fan.
2. For Clogged Filters:
   • Isolate the filter section. Drain the fluid (if it is water). Remove and clean or replace the filter element. Reinstall and bleed the system of air (if water).
3. For Poorly Positioned/Failed Valves:
   • Inspect control valve actuators. Check that the isolation valves are completely open. Repair or replace failed actuators or valves.
4. For Low Performance Pumps/Fans:
   • Pump: Disassemble the pump. Inspect rotor for damage or fouling. Check bearings and mechanical seal. Repair or replace worn components. Reinstall and align the pump. (See ABNT NBR 14644).
   • Fan: Inspect blades for damage or dirt buildup. Check engine bearings. Clean or replace.
5. Post-Repair Check: Measure the fluid flow again. Ensure that pump suction/discharge pressures and exchanger inlet/outlet temperatures are within design parameters.

8.4. Resolution for Failed Thermostatic Expansion Valve (VET)

1. SECURITY: Locking and Tagging (LOTO). Wear full PPE. Collect refrigerant from the VET section.
2. Check Sensor Bulb: Make sure the bulb is firmly attached to the suction line in the correct position (normally between 9 and 3 o'clock), well insulated and in good thermal contact.
3. Adjust Superheat (if VET adjustable): If superheat is consistently high (underfeeding), turn the adjustment screw clockwise in small increments (1/4 turn at a time) and wait for the system to stabilize (15-20 minutes) before measuring again. If superheat is too low (overcharging), turn counterclockwise. Target superheat is generally 5-8°C.
4. Replace VET: If, after checks and adjustments, the VET does not operate correctly, it is likely to have an internal failure (obstruction, loss of charge in the bulb). Collect the refrigerant from the evaporator and liquid line, replace the VET with a new one of the same model and capacity. Evacuate and recharge the system.

8.5. Resolution for Non-Condensable Gas in the System

1. SECURITY: Locking and Tagging (LOTO). Wear full PPE.
2. Collection and Evacuation: Collect all refrigerant from the system into a recovery cylinder. Complete withdrawal is essential to remove all non-condensables.
3. Locate Point of Entry (Air Leak): After evacuation, unsustained vacuum indicates an inward leak. Locate and repair this leak according to item 8.1.
4. Deep Evacuation: Perform a deep and prolonged evacuation with a high capacity vacuum pump, reaching a minimum of 250 microns (0.33 mbar), sustaining the vacuum for several hours to ensure complete removal of moisture and air.
5. Recharge: Recharge the system with virgin refrigerant, weighed with an electronic scale, according to the manufacturer's nominal charge.

9. Preventive Measures

Implementing a robust preventative maintenance program is essential to prevent the recurrence of these failures and ensure the longevity of the equipment.

10. Spare Parts and Components

Having critical replacement parts in stock reduces downtime and maintenance costs. For availability and detailed specifications, please consult the UNITEC-D e-catalog.

To purchase these parts and many others, visit our complete e-catalog at: www.unitecd.com/e-catalog/

11. References

• ABNT NBR 5410: Low voltage electrical installations.
• NR-10: Safety in electrical installations and services.
• NR-12: Work safety on machines and equipment.
• ABNT NBR 16655: Refrigeration and air conditioning systems - Inspection and maintenance.
• ASHRAE Handbook: Refrigeration.
• Service and Operation Manuals from chiller and component manufacturers (Carrier, Trane, York, Danfoss, Emerson, etc.).
• Good Practice Guides in Industrial Refrigeration Systems (ABRAVA, SENAI).