Diagnostics and troubleshooting: Insufficient performance of an industrial cooling system

1. Description of the problem and scope of application

This manual is designed to diagnose and troubleshoot industrial refrigeration systems that are underperforming, i.e. unable to remove design heat from the process or maintain the desired coolant temperature. Such a situation can lead to reduced production efficiency, equipment damage, increased energy consumption and, in critical cases, to a complete stop of the process. The problem covers a wide range of equipment, including chillers, cooling towers, dry coolers, heat exchangers and associated pumping stations and refrigerant circulation systems. Classification of the severity of the problem:

• Critical: Complete stoppage of the production line, risk of damage to the main equipment, non-compliance of products with quality standards. Requires immediate diagnosis and intervention.
• Significant: Reduction in production line productivity, increased energy consumption, exceeding design process temperatures. Requires urgent attention.
• Minor: Small deviations from optimal temperatures, periodic activation of emergency signals, reduction of energy efficiency. Requires scheduled diagnostics.

2. Precautions

УВАГА: Під час роботи з промисловими системами охолодження існує ризик контакту з високими напругами, рухомими частинами, рідинами під тиском, екстремальними температурами та хімічно агресивними речовинами. Failure to follow safety instructions can result in serious injury or death.

• Lockout/Tagout: Always apply lockout and tagout (LOTO) procedures in accordance with EN ISO 14118 and DSTU EN 1037:2003 before performing any work that requires access to electrical or mechanical components. Check the absence of voltage with a multimeter with the appropriate protection class (CAT III/IV).
• Residual Energy: Make sure all energy storage (capacitors, springs, pressure accumulators) are discharged or locked. In systems with a refrigerant, high pressure is possible even when the equipment is turned off.
• Personal protective equipment (PPE): Always use appropriate PPE: safety glasses or shield, gloves (heat resistant, chemical resistant), protective clothing, protective shoes. When working with refrigerants, use special cryogenic gloves and face protection.
• Refrigerants: Work with refrigerants must be carried out by qualified personnel in compliance with the norms EN 378 and requirements for working with gases under pressure. Provide adequate ventilation.
• Hot surfaces: Some components (compressors, discharge lines) can be extremely hot. Use a thermometer or thermal imager to assess temperature before contact.
• Rotating parts: Avoid contact with fans, belts and pulleys when the equipment is in operation.

3. Necessary diagnostic tools

For accurate diagnosis and troubleshooting, you must have the following set of tools that meet CE and UkrSEPRO standards:

4. Initial evaluation checklist

Before starting a detailed diagnosis, it is critical to collect preliminary information and conduct a visual inspection. This will localize the problem and avoid unnecessary measurements.

5. Systematic diagnostic algorithm

This algorithm provides a consistent approach to diagnosing the problem of insufficient performance of the cooling system.

1. Heat load check:
   1. Determine the actual heat load of the process.
      • IF the actual load significantly exceeds the design THEN possible reason: exceeding the design parameters of the system.
      • IF the actual load is equal to or less than the design THEN go to point 1b.
   2. Check the temperature and flow sensors measuring the heat load.
      • IF sensors are faulty or show incorrect data THEN reason: malfunction of measuring devices.
      • IF sensors are working THEN go to point 2.
2. Assessment of fluid circulation (water, brine):
   1. Measure the pressure and temperature drop across the evaporator/condenser.
      • IF pressure drop is high and temperature drop is low THEN possible cause: low fluid flow or heat exchanger contamination.
      • IF pressure and temperature difference are normal THEN go to point 2b.
   2. Check the circulation pumps.
      • Measure the current consumption of the pump motor.
      • Measure the discharge and suction pressures of the pump.
      • IF current is below normal and pressure is low THEN possible cause: cavitation, impeller wear, or air in system.
      • IF current is higher than normal and pressure is low THEN possible cause: jamming, engine malfunction.
      • IF pump is working normally THEN go to 2c.
   3. Check the filters and piping.
      • IF filters are dirty or valves are partially closed THEN reason: clogging or incorrect setting.
      • IF fluid circulation system is normal THEN go to point 3.
3. Refrigerant and refrigeration cycle analysis:
   1. Connect the manometric station.
      • Measure suction and discharge pressure.
      • Measure the compressor suction and evaporator outlet temperatures (for overheating).
      • Measure the temperature at the condenser outlet and at the TRV inlet (for subcooling).
   2. Diagnostics based on readings:
      • IF low suction pressure, low discharge pressure, high superheat THEN probable cause: insufficient refrigerant charge.
      • IF high suction pressure, high discharge pressure, low superheat THEN probable cause: refrigerant overload or presence of non-condensable gases.
      • IF high discharge pressure, high superheat, low subcooling THEN probable cause: Condenser contamination or insufficient coolant flow through the condenser.
      • IF low suction pressure, high superheat, low subcooling THEN probable cause: TRV malfunction (blocked, closed) or partially clogged filter drier.
      • IF refrigerant is normal THEN go to point 3c.
   3. Check the condition of the compressor.
      • Listen for unusual noises.
      • Measure the vibration.
      • Measure the current consumption.
      • IF unusual noises, high vibration or abnormal current THEN cause: compressor failure.
      • IF the compressor is working THEN go to point 4.
4. Assessment of heat exchange efficiency (evaporator, condenser, cooling tower):
   1. Overview of heat exchangers.
      • IF clear signs of contamination (dust, scale, biological deposits) on the condenser fins or inside the evaporator tubes THEN reason: contamination of the heat exchange surfaces.
      • Using a thermal imager to detect cold/hot zones that indicate clogging.
      • IF no obvious contamination THEN go to point 4b.
   2. Checking the fans of the cooling room/condenser.
      • Measure the rotation speed and current consumption.
      • Check the condition of the fan blades, belts, engine.
        • IF reduced rotation speed, damaged blades, high vibration THEN reason: fan group malfunction, insufficient air flow.
        • IF fans are working fine THEN go to 4c.
   3. Analysis of water quality in the cooling tower.
      • IF high hardness, high conductivity, presence of biological deposits THEN reason: ineffective water treatment, which leads to the formation of scale and biofouling.
      • IF all previous steps failed to find the cause THEN a thorough review of design data and a possible system audit.

6. Matrix of malfunctions and causes

The following table presents typical symptoms, likely causes (ranked by likelihood), diagnostic tests needed, and expected results.

7. Root cause analysis for each malfunction

7.1. Insufficient filling of refrigerant

Explanation: This is one of the most common causes of system performance degradation. Refrigerant leakage can be caused by mechanical damage to pipelines, leaky connections, worn seals or porous welds. Even small but constant leaks lead to a significant loss of refrigerant over time. Reducing the amount of refrigerant reduces the mass flow through the system, which leads to a drop in suction pressure, increased superheat and reduced cooling capacity.

Confirmation: Measuring refrigerant pressures and temperatures with a gauge station will show abnormally low suction pressure (below 2 bar for R-134a at 0 °C evaporating) and typically high superheat (above 10-12 °C). The use of an electronic leak detector with a sensitivity of up to 3 g/year (according to EN 14624) will allow to localize the location of the leak.

Consequences: If left unchecked, this leads to compressor overheating (due to insufficient refrigerant vapor cooling of the motor), increased mechanical wear, damage to motor insulation, and eventually compressor failure.

7.2. Contamination of heat exchange surfaces (evaporator, condenser)

Explanation: Reduction of heat exchange efficiency due to the accumulation of impurities. In air-cooled condensers, it can be dust, fluff, insects on the outer surface of the lamellas. In water cooling condensers and evaporators, this is scale, biological deposits, corrosion products on the inner surfaces of the tubes. Contamination creates thermal resistance, which prevents the efficient transfer of heat between the refrigerant and the cooled medium.

Confirmation: Visual inspection of available surfaces. Measurement of the temperature difference between the refrigerant and the coolant: for the water cooling condenser ΔT can exceed 5-7 °C, for the evaporator - 3-5 °C. The thermal imager will detect "cold" or "hot" areas, indicating local clogging. Increased discharge pressure (for a dirty condenser) or reduced suction pressure (for a dirty evaporator).

Consequences: Increased power consumption (compressor works with increased load), reduced cooling capacity, premature wear of the compressor due to increased discharge pressure or insufficient suction pressure. In extreme cases, high/low pressure protection is activated.

7.3. Insufficient flow of cooling liquid or medium

Explanation: This can refer to either water/brine flow through the evaporator or air/water flow through the condenser. Reasons: partially closed shut-off or regulating valves, dirty filters, malfunction of circulation pumps (impeller wear, cavitation, air in the system) or fans (broken belts, engine malfunction, blade contamination). Insufficient flow reduces the efficiency of heat transfer, limiting the amount of heat that can be transferred.

Confirmation: Flow measurement using an ultrasonic flowmeter (compare with design 1-3 m/s for water). Evaporator/condenser pressure drop measurement (significant increase in drop indicates clogging or low flow). Checking the current consumption of pumps/fans (deviation from nominal). Visual inspection of filters and valves.

Consequences: Decreased cooling capacity, exceeding the permissible temperatures of the refrigerant and cooled liquid, increased discharge pressure (due to insufficient cooling of the condenser) or low suction pressure (due to freezing of the evaporator). Risk of damage to the compressor, freezing of the evaporator.

7.4. The presence of non-condensable gases in the system

Explanation: Non-condensable gases (usually air or nitrogen) can enter the system during installation, repair, through leaks on the suction side (when operating under vacuum) or due to refrigerant decomposition. They accumulate in the condenser, occupying the volume intended for the condensation of the refrigerant, which leads to an increase in the injection pressure and the condensation temperature at a given temperature of the refrigerant.

Confirmation: Comparison of the actual injection pressure with the condensation pressure corresponding to the temperature of the refrigerant at the condenser outlet. If the actual pressure is significantly higher (by 1-2 bar), this indicates the presence of non-condensable gases. This pressure does not correspond to the "pressure-temperature" relationship for a pure refrigerant. Using a refrigerant analyzer (if available).

Consequences: Significant increase in energy consumption, increased wear of the compressor, overheating of the compressor, reduction in cooling capacity. In the long term, it can lead to system acids, corrosion and compressor failure.

7.5. Malfunction of the thermoregulating valve (TRV)

Explanation: TRV regulates the flow of refrigerant to the evaporator, maintaining constant overheating. If the TRV is stuck in the closed position, the refrigerant flow is reduced, resulting in low suction pressure, high superheat and insufficient cooling. If it is locked in the open position, too much refrigerant enters the evaporator, which can cause the compressor to "flood" with liquid refrigerant.

Confirmation: With closed TRV – very low suction pressure, very high overheating (above 15 °C), possible icing of liquid refrigerant line to TRV. With the TRV open - low overheating (below 3 °C), possible icing of the compressor suction line, liquid shocks in the compressor. Visual inspection of TRV tubes, listening.

Consequences: Depending on the type of malfunction – overheating of the compressor, destruction of the valve group of the compressor due to hydraulic shocks, reduction of system performance.

8. Step-by-step troubleshooting procedures

8.1. Refrigerant leak elimination and refueling

1. Leak detection: Using an electronic leak detector (EN 14624), carefully inspect all connections, valves, solder joints, welds, seals, capillary tubes. Pay special attention to connections subject to vibration.
2. Усунення витоку: Залежно від характеру витоку: підтягнути різьбові з'єднання (момент затягування відповідно до рекомендацій виробника, наприклад, 20-30 Нм для стандартних гайок), замінити ущільнення, виконати ремонт пайки або зварювання.

   CAUTION: Before any repair work that requires depressurizing the system, make sure the system is de-energized and locked out (LOTO) and the refrigerant pressure is reduced to atmospheric or pumped to the receiver.

3. Evacuate the system: After the leak is fixed, connect the vacuum pump to the service ports. Evacuate air and moisture to a deep vacuum of 0.3-0.5 mbar (200-350 micron Hg) and hold for a minimum of 30 minutes to test for tightness.
4. Refrigerant charging: Charge the system with new refrigerant according to the equipment data sheet using an accurate electronic scale. Usually, refueling is carried out in the liquid phase in the liquid line or in the receiver (if the system is working).
5. Check operation: After refueling, start the system and check the pressures, superheat (4-8 °C at the compressor suction) and subcooling (4-7 °C at the condenser outlet).

8.2. Cleaning of heat exchange surfaces

1. Air cooling condenser contamination:

   1. CAUTION: Before cleaning the air cooling condenser, make sure all fans are off, de-energized and locked (LOTO).

   2. Remove large dirt (leaves, fluff) by hand.
   3. Wash the lamellas with a stream of water under pressure (max. 10-15 bar) or compressed air from the inside to the outside. Use special detergents to clean the slats if the contamination is severe. Follow the detergent manufacturer's instructions.
   4. Check the condition of the slats. Crumpled lamellas can be carefully straightened with a special comb.
2. Water Cooling Condenser and Evaporator Contamination:

   1. CAUTION: Before chemical cleaning or disassembly, make sure the system is de-energized and locked out (LOTO) and the coolant is drained.

   2. Drain the coolant from the circuit.
   3. Wash the heat exchanger with a solution of a special chemical agent to remove scale or biological deposits. The procedure should be carried out in accordance with the instructions of the manufacturer of the heat exchanger and detergent, using a circulation pump and controlling the pH of the solution. Solutions based on citric or sulfamic acid are used to remove scale, and biocides are used for biofouling.
   4. After washing, neutralize the solution and thoroughly rinse the heat exchanger with clean water until the pH is neutral.
   5. Check the quality of washing visually or using an endoscope.

8.3. Restoration of fluid flow

1. Check and Adjust Valves: Make sure all stop valves are fully open and control valves are operating correctly and set to design flow rate.
2. Cleaning the filters:

   CAUTION: Before opening the filter, make sure that the pressure in the circuit is relieved.

   Open and clean the coarse and fine filters. Replace the filter elements if they are heavily soiled or damaged.
3. Bleeding the system: Use air vents at the highest points of the system. Start the pump and gradually open the air vents until water flows without bubbles.
4. Diagnosis and repair of pumps:
   1. If the measured parameters of the pump (current, pressure, vibration) indicate a malfunction, disassemble it (after LOTO and draining the liquid).
   2. Inspect the impeller for wear, damage, or clogging.
   3. Check the condition of bearings and seals.
   4. Repair or replace faulty components. Assemble the pump, check the alignment of the shafts (misalignment tolerance no more than 0.05 mm).

8.4. Removal of non-condensable gases

CAUTION: This procedure requires knowledge of refrigeration techniques and may release refrigerant into the atmosphere unless special recovery equipment is used.

1. Connect the service station to the highest point of the capacitor.
2. Cool the condenser (if possible) to reduce the refrigerant pressure.
3. Slowly open the valve to vent non-condensable gases. This procedure is critical, as refrigerant will also be lost during rapid digestion. Use the temperature/pressure control method to determine when pure refrigerant begins to bleed.
4. Using automatic non-condensable gas separators or contacting a specialized service company for professional cleaning is recommended.

8.5. Repair or replacement of TRV

1. CAUTION: Before replacing the TRV, it is necessary to pump the refrigerant from part of the system or completely into the receiver, and then block the equipment (LOTO).

2. Drain the refrigerant from the evaporator circuit.
3. Disassemble the faulty TRV. Pay attention to the correct position of the thermal balloon and its fastening.
4. Install the new TPR, making sure the flow direction is correct and the thermoball is securely attached (in a horizontal position, on the top of the suction line, preferably after the heat exchanger, if applicable).
5. Vacuum the circuit and fill in the refrigerant (see point 8.1).
6. Adjust the TRV superheat according to the manufacturer's recommendations (typically 4-8 °C).

9. Preventive measures

Prevention is a key element in the reliable operation of the cooling system.

10. Spare parts and components

The availability of critical spare parts in the warehouse is a guarantee of quick restoration of the equipment's operability. Refer to UNITEC-D e-catalog to order.

11. Links

• DSTU EN 1037:2003 Machine safety. Unexpected Start Prevention (EN 1037:1995, IDT).
• EN ISO 14118:2018 Safety of machinery — Prevention of unexpected start-up.
• EN 378 (all parts) Refrigerating systems and heat pumps — Safety and environmental requirements.
• EN 14624:2012 Performance of leak detectors and leak testing methods for refrigerants.
• Operation and maintenance manuals from refrigeration manufacturers (eg Daikin, Carrier, Trane, Bitzer).
• Relevant sections ISO 50001 (Energy Management Systems) and ISO 14001 (Environmental Management Systems) regarding energy efficiency and refrigerant management.
• UNITEC-D recommendations for optimal selection of components for cooling systems.