Diagnostic Guide: Insufficient Cooling Capacity of Industrial Systems

1. Description and Scope of the Problem

Ce guide de diagnostic technique est conçu pour les techniciens de maintenance et les ingénieurs chargés de l'exploitation et de l'entretien des systèmes de refroidissement industriels. Il aborde la problématique critique de la capacité de refroidissement insuffisante, un dysfonctionnement pouvant entraîner des arrêts de production, des dommages aux équipements et une perte d'efficacité énergétique significative. L'objectif est de fournir une méthodologie systématique pour identifier la cause première de cette défaillance et d'appliquer des solutions correctives efficaces.

Main Symptoms

• Chilled water (or other heat transfer fluid) temperature above set point.
• Process return temperature higher than expected.
• Prolonged production equipment cooling cycle times.
• Abnormal increase in compressor discharge pressure.
• Reduction in apparent refrigeration efficiency.
• Higher electrical consumption of compressors for a given thermal load.

Affected Equipment

This methodology applies to a wide range of industrial cooling systems, including:

• Vapor compression chillers (chillers) (with air or water condensers).
• Cooling towers.
• Heat exchangers (plate, tubular, etc.).
• Secondary heat transfer fluid circuits (chilled water, glycol).
• Specific process refrigeration systems (e.g. food production lines, aeronautical test equipment, chemical reactors).

Severity Classification

• Critical: Production shutdown imminent or in progress. High risk of irreversible damage to primary process equipment. Requires immediate intervention.
• Major: Significant degradation of production performance, increase in energy costs. Requires rapid planning of corrective actions.
• Minor: Slight deviation in operating parameters, limited impact on production but potentially precursor to a major failure. Warrants a planned investigation.

This guide complies with the diagnostic requirements of the NF EN 378 standard relating to refrigeration systems and heat pumps, as well as the maintenance principles defined by the AFNOR NF X 60-010 standard.

2. Mandatory Security Measures

Working on industrial cooling systems presents significant risks related to electrical energy, pressurized fluids, extreme temperatures and refrigerants. Strict compliance with safety procedures is non-negotiable for the protection of personnel and equipment.

CRITICAL WARNING: Before any intervention, it is obligatory to comply with the lockout and untagout procedures (Lockout/Tagout - LOTO) in accordance with standard NF C 18-510 for access to electrical installations, and with the company's internal directives. Failure to do so could result in serious or fatal electric shock.

REFRIGERANTS: Handle refrigerants with extreme caution. Some fluids are toxic, flammable or asphyxiating (especially in confined spaces). Always use appropriate personal protective equipment (PPE) and ensure adequate ventilation. Refer to the safety data sheet (MSDS) of the fluid concerned. Operations on the refrigeration circuit must be carried out by personnel certified according to the F-Gas regulations (Regulation (EU) No. 517/2014).

HIGH PRESSURES: The refrigeration and hydraulic circuits operate under high pressures. Never attempt to open or loosen any fitting or component until pressure has been completely released and checked. Use certified pressure gauges. The rupture of a pressurized component can project fragments and fluids at high velocity, causing serious injury.

EXTREME TEMPERATURES: Surfaces may be extremely hot or cold. Use thermal protective gloves to avoid burns or frostbite.

STORED ENERGY: Components such as electrical capacitors, pressure accumulators, springs and hydraulic systems can store residual energy even after the power is turned off. Check and discharge these energies before any manipulation.

Personal Protective Equipment (PPE) Required

• Protective gloves resistant to chemicals and cuts (compliant with EN 388 and EN 374).
• Safety glasses or face shield (EN 166 compliant).
• Safety shoes (EN ISO 20345 compliant).
• Long-sleeved workwear.
• Hearing protection (plugs or headphones) if the sound level exceeds 80 dB(A).
• Respiratory protection device if there is a risk of refrigerant leak in a confined space (EN 140/143 compliant).

3. Required Diagnostic Tools

Accurate diagnosis of insufficient cooling capacity requires the use of specific and calibrated measuring tools. Reliable measurements are essential for correct analysis and appropriate maintenance decisions. All tools must be checked and calibrated regularly according to EN ISO 9001. standards

4. Preliminary Assessment Checklist

Before undertaking an in-depth diagnosis with specific tools, a visual assessment and collection of contextual information is crucial. This step helps guide the diagnosis and avoid unnecessary investigations. It must be carried out rigorously and the information documented.

5. Systematic Diagnostic Scheme

This diagnostic diagram guides the technician through a series of logical checks, from initial observation to identification of the failing subsystem. Each step requires precise measurement or observation. Failure to follow this logic can lead to diagnostic errors and ineffective interventions.

1. Initial Symptom: Cooled Fluid Temperature Above Setpoint
   • Check 1.1: Process Heat Load
     1. Measure or confirm the current process heat load (kW).
        • If the thermal load is greater than the system's rated capacity:
          • Probable Cause: Cooling system overload.
          • Action: Reduce process load or consider increasing cooling capacity.
        • If the thermal load is less than or equal to the nominal capacity :
          • Proceed to Verification 1.2.
   • Check 1.2: Flow rate of heat transfer fluid in the evaporator
     1. Measure the flow rate of heat transfer fluid (water, glycol) through the evaporator (m³/h) using an ultrasonic flow meter.
        • Compare with the nominal flow rate specified by the manufacturer (tolerance ±5%).
        • If the flow is >10% lower than the nominal flow :
          • Probable Cause: Insufficient fluid flow in the secondary circuit.
          • Action: Proceed to Verification 1.3.
        • If the flow is within or slightly above the nominal flow :
          • Proceed to Verification 1.4.
   • Check 1.3: Causes of Insufficient Flow in the Secondary Circuit
     1. Check the differential pressure across the circulation pump terminals (bar).
        • If the differential pressure is low:
          • Probable Cause: Faulty pump (cavitation, weak motor, damaged impeller) or major upstream obstruction.
          • Action: Inspect the pump, check the inlet filters.
        • If the differential pressure is high:
          • Probable Cause: Obstruction downstream of the pump (clogged filter, partially closed valve, clogging of the water side evaporator).
          • Action: Check filters, valves, and consider cleaning the water side evaporator.
     2. Check the condition of the screen filters and isolation valves on the circuit.
   • Verification 1.4: Performance of the Evaporator (Refrigerant Side)
     1. Measure the suction and discharge temperatures and pressures of the compressor (refrigerating manifold).
        • Calculate the useful superheat (real suction temperature - saturation temperature at suction).
          • If the useful superheat is too high (>8 °C):
            • Probable Cause: Lack of refrigerant or insufficient refrigerant flow in the evaporator (expander underpowered, partially blocked).
            • Action: Proceed to Verification 1.5.
          • If the useful superheat is too low (<3 °C) or zero (liquid on suction):
            • Probable Cause: Refrigerant overload, expansion valve stuck open, expansion valve bulb incorrectly positioned or faulty.
            • Action: Check the load, the regulator and its sensor.
          • If the useful superheat is within the nominal range (4-7 °C):
            • Go to Check 1.6.
   • Check 1.5: Identifying a Lack of Refrigerant or Regulator Problem
     1. Check for bubbles in the liquid sight glass (if installed).
        • If bubbles are visible:
          • Probable Cause:Lack of refrigerant charge or restriction in liquid line (partially clogged filter drier).
          • Action: Check for leaks, recharge the system if necessary, check/replace the filter drier.
     2. Measure the superheat at the regulator outlet.
        • If the overheating is abnormal:
          • Probable Cause: Malfunction of the thermostatic expansion valve (defective bulb, blocked orifice, oversizing/undersizing).
          • Action: Check the regulator, clean it or replace it.
   • Check 1.6: Condenser Performance
     1. Measure the compressor discharge temperature and pressure.
        • Calculate the subcooling (condensing temperature - liquid temperature at the condenser outlet).
          • If subcooling is insufficient (<3°C):
            • Probable Cause: Loss of condenser capacity.
            • Action: Proceed to Verification 1.7.
          • If subcooling is excessive (>10°C):
            • Probable Cause: Refrigerant overload or condenser air/water flow rate too high (rarely the primary cause of insufficient capacity).
            • Action: Check the refrigerant charge.
          • If subcooling is within rated range (4-7°C) :
            • Condenser performance is probably OK. The problem lies elsewhere. Review previous steps.
   • Check 1.7: Causes of Condenser Capacity Loss
     1. Air Condenser:
        • Check the condition of the fins: clogging (dust, leaves, pollen).
          • If clogged:
            • Probable Cause: Reduced heat exchange.
            • Action: Clean the fins (compressed air, low pressure water).
        • Check the operation of the fans: rotation speed (rpm), direction of rotation, damaged blades.
          • If low speed or failure:
            • Probable Cause: Insufficient air flow.
            • Action: Repair/replace fan or motor. Check the power supply.
        • Check the ambient air temperature.
          • If very high and unexpected:
            • Probable Cause: Recirculation of hot air to the condenser.
            • Action: Optimize the arrangement of equipment or ventilation of the premises.
     2. Water Condenser (Cooling Tower):
        • Check the cleanliness of the water side exchangers (biological fouling, limescale).
          • If dirty:
            • Probable Cause: Reduced heat exchange.
            • Action: Chemically or mechanically clean the exchanger.
        • Check the flow rate and temperature of the cooling water (inlet/outlet).
          • If the flow is insufficient or the inlet temperature excessive:
            • Probable Cause: Problem with the cooling tower or water circulation pump (low flow, clogging, faulty pump).
            • Action: Diagnose the cooling water circuit separately.

6. Defects-Probable Causes Matrix

This matrix correlates observed symptoms with probable causes, ranked in order of likelihood, as well as key diagnostic tests and expected results if the cause is confirmed. It serves as a quick reference to refine the diagnosis after the preliminary assessment.

7. Detailed Analysis of Root Causes of Failure

A thorough understanding of failure mechanisms is fundamental for effective diagnosis and implementation of sustainable solutions. Each probable cause previously identified is examined here in detail.

7.1. Insufficient Refrigerant Charge (Leak)

Explanation: A refrigerant charge lower than the nominal value results in a reduction in the mass of fluid circulating in the refrigeration circuit. The evaporator can no longer absorb the intended amount of heat, and the compressor must work longer or more intensely to try to reach the set temperature, often without success. Superheat at the evaporator increases, suction pressure decreases, and overall efficiency drops.

Confirmation:

• Use of an electronic leak detector (NF EN 14624 sensitivity) on all connections, welds, valves, cable glands and joints.
• Application of a foaming solution to suspect areas.
• Prolonged observation of the liquid indicator: presence of persistent bubbles, even after stabilization of the system.
• Checking subcooling at the condenser outlet: value lower than nominal (e.g.: <3°C).

Damage if not resolved: Prolonged operation with insufficient load can lead to compressor overheating due to lack of liquid refrigerant return, oil degradation (carbonization), and ultimately mechanical failure of the compressor (seizing, engine breakdown). Overconsumption of energy is also significant.

7.2. Insufficient Heat Transfer Fluid Flow (Evaporator or Condenser Side)

Explanation: Whether in the primary (refrigerant) or secondary (water/glycol) circuit, insufficient flow limits heat transfer. On the evaporator side, the heat exchange between the process fluid and the refrigerant is reduced, decreasing the cooling capacity. On the condenser side, heat rejection is hindered, increasing the condensing pressure and compressor load.

Confirmation:

• Flow measurement using an ultrasonic flow meter and comparison with manufacturer's specifications. A deviation of more than 10% from the nominal flow rate is critical.
• Measurement of differential pressures across the exchanger terminals: a high differential pressure for a low flow rate indicates an obstruction.
• Visual inspection of screen filters and strainers: visible clogging.
• Checking the amperage and rotational speed of circulation pumps: A drop in amperage or speed may indicate a mechanical or electrical failure of the pump.

Damage if not resolved:

• Evaporator side: freezing of water in the evaporator (risk of tube rupture), excessive thermal stress on the exchanger.
• Condenser side: increase in discharge pressure, triggering of high pressure safety devices, overconsumption of the compressor, reduction of its lifespan.

7.3. Clogging of Heat Exchangers

Explanation: The accumulation of deposits (limestone, sludge, biofilm, dust, leaves) on the heat exchange surfaces (fins of the air condenser, tubes of the evaporator or water condenser) creates an insulating barrier. This barrier reduces the efficiency of heat transfer, forcing the system to compensate through increased power consumption or degradation in performance.

Confirmation:

• Visual inspection: obstructed condenser fins, inspection of internal tube surfaces after disassembly (if possible).
• Measurement of surface temperatures using a thermal camera: detection of abnormal cold/hot zones indicating localized fouling.
• Calculation of the overall heat transfer coefficient (U) of the exchanger and comparison with the nominal values. A 20% decrease is significant.
• Differential pressure measurement: An increase indicates resistance to flow due to fouling.

Damage if not resolved: Reduced efficiency, excess energy consumption, corrosion under deposits, increased mechanical and thermal stresses, premature failure of the exchanger.

7.4. Regulator malfunction

Explanation: The expansion valve regulates the supply of refrigerant to the evaporator. If it is faulty (blocked open, stuck closed, poorly positioned/defective bulb), it seriously disrupts the power supply to the evaporator. A stuck closed or underpowered expansion valve causes excessive overheating and a lack of refrigerant to the evaporator. A stuck open or overcharged expansion valve can send liquid to the compressor, causing a liquid surge.

Confirmation:

• Precise measurement of useful superheat at the evaporator and superheat at the expansion valve outlet.
• Checking the positioning and insulation of the regulator bulb.
• Comparison of regulator inlet and outlet temperatures.
• Visual inspection: frost on the suction line (if liquid returning to the compressor).

Damage if not resolved: Drastic reduction in capacity, liquid blow on the compressor (serious mechanical damage), cavitation, premature wear of the compressor.

7.5. Presence of Incondensable Gases

Explanation: Non-condensable gases (air, nitrogen, etc.) can enter the refrigerant circuit during maintenance work, an incorrect vacuum extraction procedure, or a leak on the low pressure side. These gases typically accumulate in the condenser, occupying volume intended for the refrigerant and increasing the condensing pressure, thereby reducing effective subcooling and system capacity.

Confirmation:

• Abnormally high discharge pressure compared to ambient temperature (for an air condenser) or tower water temperature (for a water condenser). The condensing temperature calculated from the pressure will be significantly higher than the condenser surface temperature.
• Low or no subcooling even though the refrigerant charge is correct.
• Slow and repeated purge of the high points of the condenser (to be carried out with extreme caution and in accordance with the procedures).

Damage if not resolved: Compressor overload, excess electricity consumption, triggering of high pressure safety devices, deterioration of the oil (oxidation), internal corrosion of the circuit.

7.6. Compressor Issues

Explanation: The compressor is the heart of the refrigeration cycle. A failing compressor (worn valves, weak motor, partial seizure) can no longer provide adequate compression of the refrigerant, resulting in a drop in pumping capacity and discharge pressure, or an inability to maintain suction pressure.

Confirmation:

• Measurement of compressor motor amperage and comparison with nominal value.
• Vibration analysis: detection of bearing defects, imbalance or misalignment (according to ISO 10816-3).
• Compressor volumetric efficiency test (by comparison of mass flow rates or thermal performances).
• Abnormal noises (knocking, squeaking).

Damage if not resolved: Total compressor failure, contamination of the refrigerant circuit by metal debris, very high repair costs.

8. Step-by-Step Resolution Procedures

The following procedures detail corrective actions for each identified root cause. It is imperative to follow these steps precisely and to scrupulously respect the safety instructions mentioned at the beginning of this guide.

8.1. Resolution: Insufficient Refrigerant Charge (Leak)

1. SECURITY: Perform a complete registration (LOTO) of the equipment. Wear appropriate PPE (gloves, protective glasses, long-sleeved clothing).
2. Location of the Leak:
   • Use a high sensitivity electronic leak detector (minimum 3g/year for R410A) to systematically scan all connection points, welds, service valves, liquid sight glasses and joints.
   • In case of positive detection, confirm the leak with a foaming solution.
3. Repair of the Leak:
   • Depending on the nature of the leak, carry out the repair (tightening of the connection, replacement of the joint, welding, replacement of the component). Ensure that the repair complies with EN ISO 17670 brazing or EN ISO 9692. welding standards
4. Vacuum Draw:
   • Once the leak has been repaired, connect a powerful vacuum pump (minimum capacity 5 CFM) to the system via a manifold.
   • Pull the vacuum until reaching a level of 500 microns (0.67 mbar) or less, maintained for at least 30 minutes without pressure build-up. This guarantees the elimination of humidity and non-condensables. Check with an accurate digital vacuum gauge.
5. Recharge of Refrigerant:
   • Determine the exact mass of refrigerant required according to the manufacturer's nameplate or technical specifications.
   • Connect the refrigerant bottle (on an NF certified precision balance) to the manifold and recharge the system in liquid phase (via the liquid line) or gas (via suction if the compressor is running, carefully to avoid liquid shock), until reaching the specified mass with a tolerance of ±2%.
6. Functional Check:
   • Return the equipment to power (decommissioning).
   • Start the system and carefully monitor pressures, temperatures, superheat and subcooling. Ensure values ​​conform to design specifications.
   • Confirm there are no bubbles in the sight glass.

8.2. Resolution: Insufficient Heat Transfer Fluid Flow

1. SAFETY: Electrically lock out the pumps concerned. Insulate the sections of the hydraulic circuit.
2. Filter Inspection:
   • Check and clean all screen filters and strainers on the affected circuit. Regular cleaning (frequency to be defined depending on the contamination observed) is essential.
3. Valve Check:
   • Ensure that all isolation valves are in the fully open position and that the control valves modulate correctly (if automatic).
4. Pump Inspection:
   • If the flow rate remains low despite the previous checks, stop and isolate the pump.
   • Check the correct operation of the motor (bearings, power supply).
   • Inspect the pump impeller for any signs of fouling, wear or damage (cavitation). Replace defective parts.
   • Check the alignment of the coupling (if direct coupling) according to tolerances ISO 1940-1.
5. Air Purge:
   • Carefully bleed air from high points in the hydraulic circuit, as air can reduce pump efficiency and heat transfer.
6. Functional Verification:
   • Return the system to service. Measure the flow rate and the differential pressure across the exchangers to confirm the restoration of the nominal flow rate (tolerance ±5%).

8.3. Resolution: Clogging of Heat Exchangers

1. SECURITY: Lock out equipment. Wear appropriate PPE (gloves, glasses, respiratory protection if chemical cleaning).
2. Cleaning the Air Side (Air Condensers):
   • Use clean, dry compressed air or a high pressure cleaner (low pressure, max 50 bar, with a wide spray angle so as not to damage the fins) to clean the condenser fins. Always clean against the direction of normal air flow.
   • Straighten bent fins using a fin comb.
3. Cleaning the Water Side (Evaporators, Water Condensers):
   • Mechanical cleaning: If the exchanger is removable (plate type), dismantle it and clean the plates manually or by brushing. If tubular, use brushes or scrapers.
   • Chemical cleaning: If the exchanger is not easily removable or if the clogging is stubborn (limescale, biofilm), carry out chemical cleaning in circulation. Use specific products (inhibited acids for limescale, biocides for biofilm) compatible with the exchanger materials. Respect the recommended contact times and temperatures. Neutralize and rinse thoroughly after cleaning. (Ex: 5% citric acid solution for limescale, hydrogen peroxide solution for biofilm).
4. Functional Check:
   • After cleaning, return the system to service. Check the differential pressure across the exchanger terminals and the inlet/outlet temperatures to confirm the improvement in heat transfer.

8.4. Resolution: Regulator Malfunction

1. SECURITY: Lock out equipment. Recover the refrigerant from the circuit in an approved recovery bottle.
2. Checking the Bulb:
   • Ensure that the regulator bulb is securely fixed on the suction line, just after the evaporator outlet, and correctly thermally insulated. Replace insulation if damaged.
3. Adjustment or Replacement:
   • If the regulator is adjustable, try to adjust the useful superheat according to the manufacturer's specifications (generally 4-7 °C). Proceed with small adjustments (1/4 turn) and wait for the system to stabilize.
   • If the adjustment is ineffective or if the regulator is blocked, replace it with a new model of identical specifications (capacity, type of refrigerant, external balancing pressure if applicable). Regulators must be selected according to the EN 12284. standard
4. Vacuum and Recharge:
   • Perform a deep vacuum and precise recharge of the system as described in section 8.1.
5. Functional Check:
   • Monitor pressures, temperatures and superheat/subcool to confirm proper operation of the new regulator or proper adjustment.

8.5. Resolution: Presence of Incondensable Gases

1. SECURITY: Lock out equipment. Wear appropriate PPE.
2. Non-condensable drain:
   • Use an automatic or manual non-condensable drain. The process involves cooling the refrigerant/non-condensable gas mixture to condense the refrigerant and allow the non-condensable gases to escape.
   • For manual purging, connect an empty, evacuated recovery bottle (submerged in an ice bath if possible) to the high pressure service connection on the condenser. Open the valve very slowly to allow non-condensable gases to escape, monitoring the pressure and temperature. Close the valve as soon as the liquid refrigerant begins to flow. Repeat the operation several times.
3. Leak Check:
   • After purging, find the source of the introduction of non-condensables (leak on the low pressure circuit in depression, poor previous maintenance procedure) and repair it as described in section 8.1.
4. Vacuum and Recharge (if necessary):
   • Perform a deep vacuum and precise recharge if the amount of refrigerant has been significantly reduced during purging or repair.
5. Functional Check:
   • Recommission and monitor discharge pressure and subcooling to confirm reduction of non-condensables.

8.6. Resolution: Compressor Issues

1. SAFETY: Fully lockout the equipment, including shutting off electrical power to the compressor and isolating service valves. Collect all refrigerant from the compressor.
2. Deep Diagnosis:
   • If abnormal vibrations have been detected, carry out a more in-depth spectral analysis of the vibrations to precisely identify the nature of the fault (unbalance, misalignment, damaged bearing, loosening).
   • Check the resistance values ​​of the motor windings (according to the manufacturer's specifications).
   • Perform a dielectric test for motor insulation.
3. Repair or Replacement:
   • For minor defects (bearings, coupling), carry out repairs on site. Respect the alignment tolerances (e.g.: 0.05 mm) and tightening torques (specified by the manufacturer).
   • For major failures (seizing, motor out of order, worn internal valves), replacing the compressor is generally the most effective solution. Choose a replacement compressor with identical specifications.
4. Cleaning the Circuit (in the event of a seizure):
   • If a compressor seizure has occurred, it is imperative to clean the refrigeration circuit to remove metal residues and contaminated oil. Use specific cleaning kits (flush kits) and replace the filter drier, sight glass and system oil.
5. Vacuum and Recharge:
   • Perform a deep vacuum (target 250 microns, held for 1 hour) and precise recharge of the system with the specified type and quantity of oil and refrigerant.
6. Functional Check:
   • Recommission and monitor compressor amperage, pressures, temperatures and vibration levels. The values ​​must be stable and within specifications.

9. Preventive Measures and Surveillance

Implementing robust preventive measures and a rigorous monitoring program is essential to avoid recurrence of failures and ensure optimal and sustainable performance of industrial cooling systems. A proactive approach reduces corrective maintenance costs and minimizes unplanned production downtime.

10. Spare Parts and Critical Components

The availability of quality spare parts that meet Original Equipment Manufacturer (OEM) specifications is a critical factor in minimizing equipment downtime. UNITEC-D GmbH offers a comprehensive range of certified industrial components for cooling systems.

To order your certified spare parts and guarantee the reliability of your equipment, visit our online catalog: www.unitecd.com/e-catalog/

11. Applicable References and Standards

This guide is based on good maintenance engineering practices and recognized industrial standards. Compliance with these references ensures compliance, safety and effectiveness of interventions.

• NF EN 378: Refrigeration systems and heat pumps - Safety and environmental requirements.
• NF C 18-510: Operations on electrical installations or in their vicinity - Prevention of electrical risks.
• AFNOR NF X 60-010: Maintenance - Functions and definitions.
• EN ISO 10816-3: Mechanical vibrations - Evaluation of machine vibrations by measurements on non-rotating parts - Part 3: Industrial machines with a nominal power greater than 15 kW and nominal speeds between 120 rpm and 15,000 rpm operating on a rigid foundation.
• EN ISO 17670: Brazing - Guidelines for quality in brazing.
• EN ISO 9692: Welding and related techniques - Joint preparation.
• EN 12284: Refrigerating appliances and heat pumps - Thermostatic expansion valves - Classification, specifications and tests.
• EN 14624: Leak detection of refrigeration and air conditioning systems containing fluorinated refrigerants.
• Regulation (EU) No. 517/2014: Relating to fluorinated greenhouse gases and repealing Regulation (EC) No. 842/2006. (F-Gas Regulation).
• Specific operating and maintenance manuals from your equipment manufacturer (OEM).