Diagnostic and Resolution Guide: Low Capacity in Industrial Cooling Systems

1. Description and Scope of the Problem: Low Industrial Cooling Capacity

Low cooling capacity in an industrial system manifests itself as the inability of the equipment to maintain the desired temperature in the process or conditioned space, resulting in an unacceptable increase in fluid or ambient temperature.

This symptom can affect a wide range of equipment, including air and water chillers, cooling towers, evaporative condensers, vapor compression refrigeration systems, and heat pump systems. The severity of this problem is classified as:

• Criticism: Compromised process safety, risk of damage to sensitive equipment, imminent interruption of production.
• Major: Significant reduction in production efficiency, increase in energy consumption, degradation of product quality.
• Minor: Slight deviations from target temperature, but no immediate impact on production or safety.

This guide focuses on a structured diagnostic approach to identify the root cause of low cooling capacity, allowing for effective and lasting resolution.

2. Critical Safety Precautions

WARNING! Before any intervention on cooling systems, it is IMPERATIVE to follow appropriate safety procedures to protect personnel and prevent damage to equipment.

• Lockout and Tagout (LOTO): Ensure all power sources (electrical, hydraulic, pneumatic) are disconnected and locked out before beginning any maintenance or diagnostic work. Check the absence of voltage with a calibrated voltmeter.
• Stored Energy: Electrical capacitors, pressurized systems (refrigerant, water), springs and actuators can store dangerous energy. Ensure safe discharge of this residual energy before handling components.
• Personal Protective Equipment (PPE): Always use appropriate PPE: chemical resistant gloves (for refrigerants and water treatment fluids), safety glasses or face shields, hard hat, safety footwear and flame retardant work clothing if electrical hazard exists.
• Refrigerants: Refrigerants can cause severe frostbite on contact with the skin and eyes, and asphyxiation at high concentrations due to displacement of oxygen. Work in well-ventilated areas and use a refrigerant leak detector.
• Extreme Temperatures: Hot or very cold surfaces (pipes, compressors) can cause burns or frostbite. Use thermal gloves.
• System Pressure: Never depressurize a cooling system in an uncontrolled manner. Use refrigerant recovery equipment and calibrated pressure gauges to monitor pressure.
• Chemicals: Cooling tower water treatment chemicals can be corrosive or irritating. Consult Safety Data Sheets (SDS) and use recommended PPE.
• Rotating Components: Keep hands, tools and clothing away from moving fans, pumps and belts.

3. Essential Diagnostic Tools

The accuracy of the diagnosis depends directly on the quality and calibration of the tools used. The following table details the essential tools for this investigation:

4. Initial Evaluation Checklist

Before beginning an in-depth diagnosis, complete this checklist to collect critical data that can guide the investigation and avoid unnecessary interventions.

5. Systematic Diagnostic Flowchart

This flow chart guides the technician through a logical process to isolate the root cause of low cooling capacity. Follow the branches based on the results of your measurements and observations.

1. INITIAL SYMPTOM: Elevated Process or Environment Temperature.
   1. Verification of Thermal Load and Operating Parameters:
      • Measure inlet and outlet temperatures: Of the cooled fluid (e.g. water, glycol) in the evaporator and of the heat rejection fluid (e.g. tower water, ambient air) in the condenser.
        • Thresholds: Temperature differentials out of specification (e.g. ΔT process water < 3°C o > 6°C for a chiller designed for 5°C) indicate problems.
      • Evaluate the actual load: Has the thermal load demanded by the process increased recently?
        • If the load is significantly greater than design: The system capacity may be insufficient for the current demand. Consider process optimization or capacity addition.
        • If the load is normal or less: Proceed with the cooling system diagnosis.
      • Measure refrigerant pressures and temperatures: Use pressure gauges and contact thermometers on the compressor suction and discharge lines, evaporator inlet/outlet, and condenser.
        • Thresholds: Pressures and temperatures outside the manufacturer's operating ranges. Excessive superheating (>10°C) or insufficient subcooling (<3°C) are key indicators.
   2. If the refrigerant parameters are abnormal (low suction pressures, high discharge pressures, or both):
      1. Refrigerant Circuit:
         • Refrigerant Charge Verification:
           • Symptom: Low suction pressure, high discharge pressure (slight), low subcooling, high discharge temperature. Possible frost on the suction line or evaporator.
             1. Diagnosis: Use pressure gauges and thermometers. Calculate superheating and subcooling. Use an electronic leak detector (UNE EN 14624:2019 sensitivity) to track leaks.
             2. Expected Results:
                • Confirmed Leak: Abnormal pressures, low subcooling, possible detection of refrigerant at specific points.
                • Excess Load: Very high discharge pressure, low superheat, high subcooling. Risk of liquid hitting the compressor.
                • Correct Load: Pressures and temperatures within adequate ranges, superheating and subcooling.
         • Presence of Non-Condensable Gases:
           • Symptom: Persistently high discharge pressure, condensation temperatures higher than expected for ambient/condensation water temperature.
             1. Diagnosis: Compare the actual condensation temperature with the saturation temperature corresponding to the discharge pressure. A difference > 3°C indicates non-condensables.
         • Compressor Operation:
           • Symptom: Abnormal noises, excessive vibrations (> 4.5 mm/s RMS), current consumption below or above expected, abnormal discharge temperature.
             1. Diagnosis: Perform a vibration analysis. Measure the current consumption with a current clamp. Visually inspect the compressor.
         • Thermostatic Expansion Valve (VET) / Electronic (VEE):
           • Symptom: Excessive or insufficient superheating at the evaporator outlet. Frozen VET or poorly attached sensor bulb.
             1. Diagnosis: Measure temperatures in the suction line and sensing bulb. Physically inspect the VET/VEE.
   3. If the coolant parameters are correct but the capacity is still low:
      1. Water/Glycol Circuit (Cooled Side):
         • Insufficient Chilled Fluid Flow:
           • Symptom: Temperature delta (ΔT) between the evaporator inlet and outlet excessively high or low for the nominal flow. Low pressure in the circulation pump.
             1. Diagnosis: Measure the flow rate with an ultrasonic flow meter. Check differential pressure across evaporator and filters.
             2. Expected Results:
                • Restriction: Flow rate below the design value. Dirty filters, partially closed valves, faulty pumps, air in the system.
                • Defective Pump: Low flow rate, abnormal current consumption, vibrations.
         • Fouling in Evaporator:
           • Symptom: Large temperature ΔT across the evaporator, normal refrigerant pressures but elevated chilled fluid temperatures.
             1. Diagnosis: Evaluate the pressure drop on the water side of the evaporator. Visual inspection if possible.
      2. Heat Rejection Circuit (Condensing Side):
         • Insufficient Air Flow (Air Condenser):
           • Symptom: Discharge pressure too high. Fans not working or running at low speed. Clogged condenser fins.
             1. Diagnosis: Inspect fins visually. Measure fan motor current.
         • Insufficient Water Flow (Water Condenser / Cooling Tower):
           • Symptom: Very high discharge pressure. High condensation water temperatures.
             1. Diagnosis: Measure the water flow in the condenser with a flow meter. Check condensate water pumps. Inspect the cooling tower for blockages or deposits.
         • Fouling in the Condenser:
           • Symptom: Very high discharge pressure, high condensing water temperature ΔT, higher than normal condensation temperatures.
             1. Diagnosis: Evaluate the pressure drop on the water side of the condenser. Visual inspection if possible.
      3. Control or Instrumentation Problems:
         • Symptom: The system does not respond to load demands, incorrect setpoints, erroneous sensor readings.
           1. Diagnosis: Verify calibration of temperature and pressure sensors with reference equipment. Check the control logic in the PLC/BMS. Ensure contactors and relays are working correctly.

6. Matrix of Failures and Probable Causes

This table correlates the observed symptoms with the most probable causes, the recommended diagnostic test, and the expected result confirming the cause.

7. Root Cause Analysis for Each Failure

7.1. Insufficient Refrigerant Charge / Leaks

Explanation: Low refrigerant charge is one of the most common causes of low capacity. It causes a reduction in the mass of refrigerant circulating, which decreases heat transfer in the evaporator and condenser. The system works with incorrect suction and discharge pressures, affecting the efficiency of the compressor and its useful life.

Confirmation: Confirmed by measuring superheat and subcooling. Excessive superheating at the compressor suction (> 10°C) and/or very low subcooling at the condenser outlet (< 3°C) are clear indicators. The positive location of a leak with an electronic detector (minimum sensitivity of 3 g/year according to UNE EN 14624:2019) corroborates the diagnosis. Visual inspection may reveal oil stains at leak points.

Damage if not resolved: Prolonged low-load operation can lead to compressor overheating, lubricating oil degradation, premature bearing and winding failures, and excessive energy consumption due to low cycle efficiency.

7.2. Dirty Condenser (Fouling)

Explanation: The accumulation of dust, dirt, leaves or mineral deposits (in the case of water condensers or cooling towers) on the condenser surfaces acts as a barrier to heat transfer. This raises the condensing pressure and temperature, forcing the compressor to work harder and reducing its effective capacity.

Confirmation: Confirmed by high discharge pressure and significantly higher than normal condensing temperature, despite adequate air/water flow and correct refrigerant charge. Visual inspection of the coil fins or cooling tower fill will clearly show the obstruction. For water condensers, an increase in the water pressure drop across the condenser (> 0.5 bar above the design value) indicates internal fouling.

Damage if not resolved: Leads to overstressing of the compressor, current peaks, activation of high pressure protections, and eventual compressor failure. Drastically increases the electrical consumption of the system.

7.3. Dirty Evaporator (Fouling)

Explanation: Similar to the condenser, dirt (dust, ice, algae deposits, sludge) on the surfaces of the evaporator prevents the absorption of heat from the cooled fluid. This results in low suction pressure and low temperature differential in the cooled fluid, since the evaporator cannot efficiently transfer heat.

Confirmation: It is verified by a low suction pressure and a temperature differential of the cooled fluid (ΔT) lower than expected for the flow rate. Visual inspection of the evaporator fins or surfaces will reveal any buildup of dirt or ice. For water evaporators, an increase in the water pressure drop across the evaporator (> 0.5 bar above the design value) indicates internal fouling.

Damage if not resolved: May cause freezing of water in the evaporator (with risk of burst pipes), excessive overheating of the compressor due to lack of adequate cooling of the suction gases, and failure of the TEV due to a sensing bulb that does not receive a stable overheating signal.

7.4. Insufficient Fluid Flow (Air or Water)

Explanation: An insufficient flow of air over the condenser or evaporator (due to defective fans, clogged filters, restricted ducts) or of water/glycol through the exchangers (due to failing pumps, dirty filters, closed valves, air in the system) limits the heat transfer capacity of the equipment. The system cannot dissipate or absorb the necessary heat.

Confirmation: Confirmed by directly measuring the flow with an ultrasonic flowmeter (accuracy ±1%). A flow rate less than 80% of the design value is unacceptable. Verification of the pressure drop in filters (> 0.3 bar differential) or inspection of fans and pumps for mechanical or electrical damage (abnormal current measured with a current clamp) corroborates the diagnosis. An unusual air level in water system drains.

Damage if not resolved: High energy consumption, compressor overheating (due to low flow in the evaporator) or high discharge pressure (due to low flow in the condenser), cavitation in pumps, and premature wear of hydraulic or ventilation components.

7.5. Non-condensable Gases

Explanation: Non-condensable gases (mainly air or nitrogen) within the refrigerant circuit do not condense at normal operating pressures and temperatures. They accumulate in the condenser, taking up space that should be used by the refrigerant and increasing the partial pressure, which raises the discharge pressure of the compressor. This reduces efficiency and capacity.

Confirmation: The main indication is an abnormally high discharge pressure for the measured condensation temperature. If the condensation temperature is significantly higher (for example, > 3°C) than the saturation temperature corresponding to the discharge pressure, non-condensables are present. Contact thermometers and pressure gauges are essential for this verification.

Damage if not resolved: Significant increase in electrical consumption, overstress and overheating of the compressor, frequent high pressure cycles, and eventual compressor failure. Drastically reduces cooling capacity.

7.6. Inefficient or Defective Compressor

Explanation: A compressor that is not operating at its optimal performance cannot move the volume of refrigerant necessary to satisfy the thermal load. This may be due to defective valves, worn piston rings (in piston compressors), or deterioration of rotors (in screw or scroll compressors).

Confirmation: It is confirmed through a detailed analysis of the refrigeration cycle (P-h diagram) showing low volumetric efficiency. Clamp-on current consumption measurements that do not correspond to the load or pressures (e.g. normal current with low capacity), abnormal internal noises or vibration analysis that reveal internal mechanical failures (> 4.5 mm/s RMS in bearings or gears).

Damage if not resolved: Total loss of cooling capacity, excessive electrical consumption for the work performed, catastrophic damage to the compressor that can contaminate the entire system with metal particles.

7.7. Problems in the Thermostatic Expansion Valve (VET) / Electronic (VEE)

Explanation: The VET/VEE is critical for regulating the flow of refrigerant to the evaporator, maintaining optimal superheat. A defective valve (stuck, poorly adjusted, loose sensor bulb or loss of pressure) can cause excessive overheating (little refrigerant supply) or insufficient overheating (flooding of the evaporator and risk of liquid shock in the compressor).

Confirmation: It is verified by measuring the superheat at the evaporator outlet and comparing it with the design value (generally 4-7°C). A TEV that delivers a constant and very high superheat indicates that it is not opening enough. A TEV flooding the evaporator (low or negative superheat) may be stuck open or have the sensing bulb installed incorrectly. Visual inspection of the bulb and its contact with the suction line is critical.

Damage if not resolved: Compressor overheating due to lack of cooling of the suction gases (VET closed), or liquid slam into the compressor (VET open), both leading to premature compressor failure and low capacity.

8. Step-by-Step Resolution Procedures

8.1. Refrigerant Leak Resolution and Recharge

1. WARNING! Apply LOTO before any intervention. Use full PPE (cryogenic gloves, goggles).
2. Location: Using the electronic leak detector (sensitivity 3 g/year), systematically trace all joints, welds, valves, glands and pipe connections. Use detector foam on suspicious areas.
3. Repair: Once located, repair the leak (welding, component replacement, connection tightening). Ensure that the repair complies with UNE regulations EN 378.
4. Evacuation: Perform a complete evacuation of the system to a deep vacuum (< 500 microns, monitored with calibrated digital vacuum gauge) using a suitable vacuum pump. This eliminates moisture and non-condensable gases. Keep the vacuum for at least 30 minutes to check the tightness.
5. Recharge: Charge the system with the type and amount of refrigerant specified by the manufacturer (see data plate or OEM manual). Use a coolant scale calibrated to an accuracy of ±10 grams. Recharge in liquid phase on the high pressure side or in vapor phase on the low pressure side (with the compressor running, slowly, to avoid liquid shock).
6. Verification: Monitor pressures, temperatures, superheat and subcooling. Ensure they are within normal operating ranges. Perform a new leak detector check on the entire repaired and adjacent area.

8.2. Cleaning of Condensers and Evaporators

WARNING! Apply LOTUS. Use appropriate PPE for chemical handling if applicable (nitrile gloves, safety glasses, face shield).

8.2.1. Air Condensers and Air Evaporators

1. Dry Cleaning: With dry, clean compressed air (max. 3-4 bar pressure, do not exceed to avoid damaging fins!) blow the fins from the inside to the outside.
2. Chemical Cleaning (if necessary): Apply a specific coil cleaner, alkaline for grease or acidic for mineral deposits (follow manufacturer's instructions). Leave to act and rinse thoroughly with low pressure water.
3. Fin Straightening: Use a fin comb to straighten bent fins, improving airflow.

8.2.2. Water Condensers (Shell & Tube, Plates) and Water Evaporators

1. Isolation and Drainage: Isolate the exchanger from the water circuit and drain it completely.
2. Mechanical Cleaning: If they are tube and shell, use mechanical brushes or high pressure hydrocleaning. For plates, separate and clean plates individually if soiling is severe.
3. Chemical Cleaning: Circulate a chemical cleaning solution (acidic for lime, alkaline for biofilm) through the exchanger (per manufacturer's recommendations and SDS). Monitor pH.
4. Rinse and Neutralization: Rinse thoroughly with clean water. If acids were used, neutralize the system before returning it to service.
5. Verification: Measure the pressure drop across the exchanger to confirm reduction in clogging (< 0.2 bar).

8.3. Restoration of Fluid Flow (Air or Water)

1. WARNING! Apply LOTO for pumps and fans.
2. Clogged Filters: Clean or replace all air and water filters. Measure pressure drop across filters after maintenance.
3. Defective Pumps: Inspect the pump for abnormal noises, vibrations. Measure the current consumption with a current clamp and compare it with the data plate. Check the coupling and condition of the impeller. Repair or replace as necessary.
4. Defective Fans: Check that the fan motors rotate freely and that the blades are not damaged. Measure the motor current. Repair or replace if necessary. Ensure that the belts are correctly tensioned (deflection of 1.5 cm for each meter of distance between pulley centers with 10 N of force).
5. Closed/Partially Closed Valves: Visually inspect and manually operate all isolation and balancing valves in the circuit to ensure they are fully open.
6. Air in the Water/Glycol System: Systematically purge air from high points in the system using the air bleeders.
7. Verification: Measure the flow rate of the fluid (air or water) with the appropriate instruments (anemometer, ultrasonic flowmeter) to confirm that it has returned to the design values ​​(±5%).

8.4. Non-condensable Gas Purge

1. WARNING! Use appropriate PPE. Work in a ventilated area.
2. Isolation: Isolate the liquid receiver or condenser from the rest of the system.
3. Purge: With the compressor off and pressures stabilized (preferably with the system cooling so that the liquid refrigerant settles at the bottom and non-condensables at the top), slowly open a bleed valve at the top of the receiver or condenser. Use a hose connected to a recovery tank to minimize emission.
4. Monitoring: Monitor system pressure. Close the valve as soon as the pressure begins to drop rapidly, indicating that pure refrigerant is beginning to escape.
5. Repeat: Repeat the process several times with intervals of a few minutes until the difference between the condensation temperature and the saturation temperature is less than 2°C.

8.5. Adjustment or Replacement of VET/VEE

1. WARNING! Apply LOTUS. Refrigerant recovery required if valve needs to be replaced.
2. Superheat Diagnosis: Measure the refrigerant superheat at the evaporator outlet.
3. Adjustment (if possible): If the TEV has an adjustment screw, turn it in small increments (1/4 turn) to increase (turn clockwise) or decrease (turn counterclockwise) the superheat. Wait 15-20 minutes between adjustments for the system to stabilize.
4. Sensing Bulb Inspection: Ensure the TEV bulb is firmly attached to the evaporator suction line in a correct position (generally at 4 or 8 o'clock on horizontal pipes) and thermally insulated.
5. Replacement: If the desired superheat is not achieved or the valve is physically damaged, recover the refrigerant, unsolder the old valve and solder a new one of identical or equivalent specifications (UNE EN 378). Perform an evacuation and recharge of the affected section.
6. Check: Monitor overheating and ensure stable operation.

9. Preventive Measures

Implementing a preventive maintenance program is critical to avoid the recurrence of low capacity failures.

10. Spare Parts and Critical Components

Having critical spare parts available significantly reduces downtime. The following are key components that should be considered for the inventory, along with their reference in the UNITEC-D catalogue:

To purchase these and other critical components, visit our E-UNITEC-D Catalog, where you will find parts with CE and AENOR certifications that meet the most demanding industrial standards.

11. References

• UNE EN 378:2018 - Refrigeration systems and heat pumps. Safety and environmental requirements.
• ISO 10816-3:2009 - Measurement and evaluation of mechanical vibration of machines.
• ASHRAE Handbook - Refrigeration, HVAC Systems and Equipment - Technical guide for the design and operation of air conditioning and refrigeration systems.
• OEM Service and Operation Manuals: Always refer to the specific documentation for your equipment.
• Related UNITEC-D Maintenance Guides: For specific topics on components or equipment.