Diagnosis and Troubleshooting Guide for Industrial Refrigeration Systems with Insufficient Capacity

1. Problem Description and Scope

The insufficient capacity of an industrial refrigeration system manifests itself when the equipment is unable to remove the necessary thermal load, resulting in temperatures of the refrigerated fluid or process environment above the design or setpoint values. This can lead to a series of operational impacts, from reduced efficiency and increased energy consumption to interrupted production and compromised product quality.

This guide addresses common symptoms and causes associated with inadequate capacity in refrigeration systems, covering:

• Chillers: Liquid chillers (water or glycol solutions), whether air or water condensed.
• Cooling Towers: Essential heat rejection equipment for water-condensed chillers and other industrial processes.
• Heat Exchangers: Critical components for heat transfer between fluids.
• Pumps and Fans: Fundamental elements for the circulation of fluids and air.

Severity Rating:

• Critical: Total failure or drastic reduction in capacity that prevents production from continuing. Requires immediate intervention.
• Majority: Reduced capacity that affects process efficiency, increases operating costs and/or compromises product quality. Requires priority solution.
• Minor: Small variation in capacity that does not directly impact production, but indicates loss of efficiency and potential for future failures. Requires planning for correction.

2. Safety Precautions

IT IS CRITICAL to strictly follow safety procedures before any intervention in refrigeration systems. Noncompliance may result in serious injury or death.

• Lockout and Tagout (LOTO - Lockout/Tagout):

  In accordance with NR-10 and NR-12, isolate all energy sources (electrical, mechanical, hydraulic, pneumatic) and apply blocking devices and warning labels. Check the absence of voltage with a calibrated voltmeter.

• Personal Protective Equipment (PPE):

  Always wear safety glasses or a face shield, chemical and thermal resistant gloves, a helmet, safety shoes and ear protection. When handling refrigerant fluids, use cryogenic gloves.

• Stored Energy:

  Valves, pipes and compressors can contain fluids under high pressure. Relieve pressure from hydraulic or pneumatic systems before dismantling components. Electrical capacitors can retain a dangerous charge even after power is disconnected; download them properly.

• Fluid Soft Drinks:

  Many refrigerants are asphyxiating, irritating or flammable. Operate in well-ventilated areas. Avoid direct contact with skin and eyes. Never heat refrigerant cylinders directly with a flame.

• Extreme Temperatures:

  System components may be extremely hot (compressor discharge) or cold (suction line, expansion). Wear appropriate gloves to prevent burns or frostbite.

3. Required Diagnostic Tools

Diagnostic accuracy depends on the use of calibrated measuring equipment suited to the task. Below is a list of essential tools:

4. Initial Assessment Checklist

Before beginning any in-depth diagnosis, collect the following information. This step is CRITICAL to correctly direct the investigation and avoid wasting time on secondary failures.

5. Systematic Diagnosis Flowchart

This flowchart guides the technician through a logical process to identify the root cause of insufficient capacity. Follow the sequence for an efficient approach.

1. Initial Symptom: Temperature of the cooled fluid above the setpoint or excessive cooling time.
1. Check Cooled Fluid Flow (Water/Glycol):
1. Is there adequate flow? (Use an ultrasonic flow meter or pressure gauges before/after the pump and heat exchanger)
• If NO:
  1. Check circulation pump: Noise, vibration, electric current.
  2. Check blocking/control valves: Position, locking.
  3. Check filters: High differential pressure across filter.
  4. Check for obstructions in the piping: Freezing points, deformations.
  5. Probable Cause: Pump failure, closed/defective valves, clogged filters, obstruction in the piping.
• If YES: Proceed to the next step (Heat Exchanger Analysis).
2. Check Heat Exchanger (Evaporator) Efficiency:
1. Is Delta T (cooled fluid inlet-outlet) within the expected range? (Use an immersion thermometer)
• If NO (Delta T too low for the load):
  1. Check for dirt/scale in the evaporator: High fluid pressure drop, high approach temperatures.
  2. Check refrigerant flow in the evaporator: Inadequate distribution on the fins (thermographic camera).
  3. Probable Cause: Fouling in the evaporator, restricted/poorly distributed refrigerant flow.
• If YES (normal Delta T for the load): Proceed to the next step (Refrigerant Circuit Analysis).
3. Analyze Refrigerant Circuit (Compressor, Condenser, Expansion Valve):
1. Refrigerant Pressures and Temperatures (Digital Manifold):
• Abnormally Low Suction Pressure:
  1. Check Thermostatic Expansion Valve (VET): Very high superheat (VET undersized, clogged or failing).
  2. Check Restriction in the Suction Line/Dryer Filter: Large pressure drop before the compressor.
  3. Check Refrigerant Charge: Low charge (undercharge).
  4. Probable Cause: Faulty/incorrectly adjusted VET, clogged filter drier, refrigerant undercharge.
• Abnormally High Discharge Pressure:
  1. Check Condenser Cleanliness: Dirty coils (air chillers), clogged nozzles/dirty basins (cooling towers).
  2. Check Air/Water Flow in the Condenser: Failure of fans, tower pumps, clogging of pipes.
  3. Check Refrigerant Charge: Excessive charge (overload) or presence of non-condensable gases.
  4. Probable Cause: Dirty condenser, insufficient air/water flow, refrigerant overload, non-condensable gases.
• Abnormally High Suction and Discharge Pressures:
  1. Check Compressor: Defective valves, mechanical failure.
  2. Probable Cause: Inefficient compressor.
• Abnormally Low Suction and Discharge Pressures:
  1. Check Compressor: Defective valves, mechanical failure.
  2. Probable Cause: Inefficient compressor.

6. Matrix of Failures and Probable Causes

The following table presents common symptoms, their likely causes (ranked by frequency), specific diagnostic tests and expected results to confirm the cause.

7. Root Cause Analysis for Each Failure

7.1. Dirty/Clogged Condenser

• Detailed Explanation: The condenser is responsible for rejecting heat from the refrigerant into the environment (air or water). Accumulation of dirt, dust, scale or biofilm formation in your coils (air chillers) or tubes (water chillers/cooling towers) prevents efficient thermal exchange. This causes an increase in condensation temperature and pressure, reducing the temperature differential available to the evaporator, and consequently the refrigeration capacity.
• How to Confirm: Visual inspection of the coils (air) or filling the Delta T test on the condenser (air: air inlet/outlet; water: water inlet/outlet). In water chillers, checking the approach temperature between the condenser leaving water and the refrigerant condensing temperature (ideally < 5°C) is CRITICAL. A high Delta P (differential pressure) between the water inlet and outlet in the condenser indicates clogging.
• Damage if Unresolved: Increased energy consumption due to higher discharge pressure, premature compressor wear (operating under greater load), and eventual compressor failure.

7.2. Refrigerant Undercharge

• Detailed Explanation: Insufficient quantity of refrigerant in the system due to leaks or incorrect recharging leads to lower mass flow through the evaporator. This results in excessive superheating of the refrigerant at the evaporator outlet as there is less liquid to evaporate and absorb heat. The suction pressure will be low, and the compressor will have to work harder to move the same amount of heat, but with lower efficiency.
• How to Confirm: Use the digital manifold to measure suction and discharge pressures and temperatures. Calculate superheat (actual suction line temperature minus suction saturation temperature) and subcooling (discharge saturation temperature minus actual liquid line temperature). For underloading, superheating will be high (>8°C) and subcooling low (<3°C). An electronic leak detector is essential to identify the source of the problem.
• Damage if not resolved: Excessive compressor overheating, oil burning (reducing lubrication), wear of internal components and eventual compressor failure.

7.3. Scale/Fouling in the Evaporator

• Detailed Explanation: Similar to the condenser, the evaporator can accumulate mineral scale, biofilm or dirt on the heat exchange surface. This creates a thermal barrier that prevents the refrigerant from efficiently absorbing heat from the fluid to be cooled. The result is insufficient Delta T (low heat exchange) in the evaporator, even with adequate refrigerant and fluid flow.
• How to Confirm: Monitor Delta P across the evaporator. A significant increase (>0.5 bar) over design values ​​indicates fouling. Internal visual inspection (if possible) will confirm buildup.
• Damage if not resolved: Drastic reduction in capacity, increased energy consumption, and in severe cases, freezing of the evaporator due to low heat transfer, which can cause structural damage to the equipment.

7.4. Insufficient Chilled Fluid Flow

• Detailed Explanation: If the flow of water or glycol solution through the evaporator is less than designed, the ability to absorb heat from the process will be compromised. This can be caused by pump failure, partially closed or clogged valves, clogged filters, or restrictions in the piping. Low flow results in a high Delta T in the evaporator (the passing fluid has time to absorb more heat), but the total amount of heat removed is low.
• How to Confirm: Use an ultrasonic flow meter to check the actual flow. Measure the differential pressure across the pump (Delta P) and discharge line. Check the electrical current of the pump. A clogged filter will have a high Delta P across it.
• Damage if Unaddressed: Reduced efficiency, risk of evaporator freezing, premature pump wear due to off-curve operation.

7.5. Excess Refrigerant Charge

• Detailed Explanation: An excessive amount of refrigerant in the system (overload) causes part of the liquid to accumulate in the condenser. This reduces the heat exchange area available for condensation, increasing the discharge pressure and, consequently, the condensation temperature. Superheat will be low and subcooling will be high, indicating that the refrigerant is remaining too long in the condenser and liquid line.
• How to Confirm: The digital manifold will indicate abnormally high discharge pressure and high subcooling (>10°C). Superheat will typically be low (<3°C).
• Damage if Unresolved: Increased discharge pressure, compressor overload, increased energy consumption, and possible damage to the compressor due to high pressure.

7.6. Non-Condensable Gases in the System

• Detailed Explanation: The presence of non-condensable gases (such as air, nitrogen) in the refrigeration system creates an insulating layer on the surface of the condenser, making heat transfer from the refrigerant difficult. This results in a high discharge pressure for the corresponding condensing temperature, as the total pressure is the sum of the pressure of the refrigerant and the non-condensable gases.
• How to Confirm: Use the digital manifold and compare the actual condensing temperature with the saturation temperature corresponding to the discharge pressure. A significant difference (more than 1.5 bar pressure above the expected saturation pressure) indicates the presence of non-condensable gases.
• Damage if Unaddressed: Dangerously high discharge pressure, increased energy consumption, and overload and eventual compressor failure.

7.7. Inefficient Compressor

• Detailed Explanation: A compressor can become inefficient due to wear on valves, piston rings (in reciprocating compressors) or rotors (in screw compressors). This results in the inability to move the required volume of refrigerant, leading to suction and discharge pressures closer together than normal, or lower electrical currents than expected for the load.
• How to Confirm: Measure suction and discharge pressures. If both are abnormal (e.g., both low or both high) in relation to the load conditions and temperatures, and the compressor electrical current is lower than expected, or if there are abnormal noises (knocking, scraping) and excessive vibration (RMS > 7.1 mm/s for bearings), the compressor may be inefficient.
• Damage if Unresolved: Total loss of refrigeration capacity, catastrophic compressor failure, generating high repair costs and downtime.

8. Step-by-Step Resolution Procedures

After identifying the root cause, follow the specific procedures for correction. REMEMBER TO APPLY THE LOTUS AND USE APPROPRIATE PPE AT ALL STEPS.

8.1. Dirty/Clogged Condenser

1. Lockout and Tagout (LOTO):

   De-energize and isolate the chiller or cooling tower.

2. Air Condenser Cleaning:

   1. Use compressed air (max. 6 bar) to remove loose dirt in the opposite direction to the normal air flow.
   2. Apply a specific cleaning product for coils (biodegradable and non-corrosive) with a low pressure sprayer.
   3. Leave it on for the time recommended by the manufacturer (usually 10-15 minutes).
   4. Rinse thoroughly with low pressure water.

3. Water Condenser/Cooling Tower Cleaning:

   1. Drain the water from the condenser circuit or tower basin.
   2. Perform mechanical cleaning with suitable brushes (for shell and tube condensers) or low pressure hydrojetting (for filling towers).
   3. For severe scale, apply a chemical descaler (citric acid, sulfamic acid) following the manufacturer's recommendations and neutralizing after cleaning.
   4. Rinse and refill the system with treated water.

4. Post-cleaning Check:

   Energize system, monitor Delta T, pressures and temperatures to confirm efficiency improvement.

8.2. Refrigerant Undercharge

1. Lockout and Tagout (LOTO):

   De-energize the chiller.

2. Leak Detection:

   Use an electronic leak detector to locate the source of the leak.

3. Leak Repair:

   Carry out the repair in accordance with the best practices of ABNT NBR 15830 (Refrigeration and Air Conditioning Systems - Maintenance Procedures).

4. System Evacuation:

   Connect the vacuum pump to the system through the manifold and evacuate until a deep vacuum (250 microns or 0.33 mbar) is reached, maintaining it for at least 30 minutes to ensure the removal of moisture and non-condensable gases.

5. Coolant Refill:

   With the system evacuated, recharge the refrigerant in the liquid phase (for zeotropic mixtures) using a precision electronic balance (tolerance of ± 10g) up to the charge specified by the manufacturer. Monitor superheating and subcooling during charging.

6. Post-reload Check:

   Turn on the chiller and monitor pressures, temperatures, superheating and subcooling. Make sure the parameters are within the manufacturer's specifications.

8.3. Scale/Fouling in the Evaporator

1. Lockout and Tagout (LOTO):

   De-energize and isolate the chiller.

2. Evaporator Drainage:

   Drain the cooled fluid from the evaporator.

3. Chemical Cleaning (for plate or shell and tube evaporators):

   1. Circulate an acidic cleaning solution (e.g. 5-10% citric acid, or specific descaling agent) heated to 40-50°C, using an auxiliary pump.
   2. Maintain circulation for the recommended time (generally 4-8 hours), monitoring the pH of the solution.
   3. Drain the cleaning solution and rinse thoroughly with clean water until the pH of the rinse water is neutral.
   4. Neutralize the cleaning solution before disposal, in accordance with environmental legislation.

4. Mechanical Cleaning (for shell and tube evaporators):

   Use appropriate nylon or metal brushes to remove scale from the pipes.

5. Post-cleaning Check:

   Recharge the system with fluid, energize the chiller, and monitor evaporator Delta P, Delta T, and capacity.

8.4. Insufficient Chilled Fluid Flow

1. Lockout and Tagout (LOTO):

   De-energize and isolate the pump and relevant valves.

2. Pump Check:

   1. If the pump is inoperative: Check the electrical supply (multimeter), fuses/circuit breakers, and motor integrity.
   2. If the pump is operating at low flow: Check the direction of rotation, obstructions in the volute, impeller wear, shaft alignment (visual inspection and vibration analyzer).

3. Valve Check:

   Confirm that all shutoff valves are fully open. Inspect control valves for sticking or failure.

4. Filter Cleaning:

   Clean or replace Y or basket filters that show high Delta P.

5. Pipe Inspection:

   Check for deformations, dents or sedimentation in the piping that could be causing restriction.

6. Post-intervention Check:

   Energize the system, monitor the flow with an ultrasonic meter, Delta P of the pump and Delta T of the evaporator.

8.5. Excess Refrigerant Charge

1. Lockout and Tagout (LOTO):

   De-energize the chiller.

2. Refrigerant Collection:

   Connect a refrigerant recovery station and an empty recovery cylinder to the system through the manifold. Collect excess refrigerant, monitoring pressure and subcooling to manufacturer's ideal values.

3. Refrigerant Weighing (optional, but recommended):

   If there is any doubt about the correct amount, collect all the refrigerant, weigh it, and refill the exact amount specified by the manufacturer.

4. Post-collection Verification:

   Turn on the chiller and monitor pressures, temperatures, superheat, and subcooling to ensure they are within specifications.

8.6. Non-Condensable Gases in the System

1. Lockout and Tagout (LOTO):

   De-energize the chiller.

2. Partial/Complete Collection:

   If the quantity is small, you can try to vent small quantities through the condenser service valve (with care and environmental responsibility). For large quantities, collect all refrigerant in a recovery cylinder, evacuate the system and recharge with virgin refrigerant.

3. System Evacuation:

   Connect the vacuum pump and evacuate the system up to 250 microns (0.33 mbar), maintaining it for a long time (minimum 1 hour).

4. Coolant Refill:

   Recharge the system with the exact amount of refrigerant specified by the manufacturer.

5. Post-intervention Check:

   Turn on the chiller and monitor pressures and temperatures, checking the relationship between discharge pressure and condensing temperature.

8.7. Inefficient Compressor

1. Lockout and Tagout (LOTO):

   De-energize and isolate the compressor.

2. Refrigerant Collection:

   Collect all the refrigerant from the circuit where the compressor is inserted.

3. Compressor Uninstallation:

   Disconnect piping, electrical wiring and assemble lifting tools. Safely remove the compressor.

4. Replacement or Repair:

   Install a new or remanufactured compressor, or send your existing compressor for repair to a specialized workshop. For replacement, make sure the new compressor is the same model and specifications.

5. Evacuation and Recharge:

   After installation, evacuate the system and recharge with the specified amount and type of refrigerant and oil.

6. Post-replacement check:

   Turn on the chiller, monitor pressures, temperatures, electrical currents and vibrations. The alignment of the engine and compressor (if separated) is CRITICAL and must be checked with a laser aligner (maximum tolerance of 0.05 mm).

9. Preventive Measures

Preventative maintenance is key to preventing insufficient capacity issues from recurring and ensuring the longevity of refrigeration systems. The table below details monitoring strategies and methods.

10. Spare Parts and Components

Having quick access to quality replacement parts is essential to minimize downtime. UNITEC-D GmbH offers a wide range of components for industrial refrigeration systems.

For high-quality original or equivalent spare parts and components, visit our e-catalog: www.unitecd.com/e-catalog/

11. References

• ABNT NBR 16401-1:2008 - Air conditioning installations - Centralized and unitary systems - Part 1: Projects.
• ABNT NBR 15830:2010 - Refrigeration and air conditioning systems - Maintenance procedures.
• NR-10: Safety in Electricity Installations and Services - Ministry of Labor and Employment.
• NR-12: Occupational Safety in Machinery and Equipment - Ministry of Labor and Employment.
• Operation and Maintenance Manuals from the Manufacturer (OEM) of the chiller/refrigeration system.
• ASHRAE Handbook - Refrigeration (technical reference for refrigeration engineering).