Troubleshooting: Exceeding the dew point in compressed air dryers

1. Description of the problem and scope of application

This manual provides systematic procedures for diagnosing and troubleshooting problems associated with exceeding the dew point in compressed air preparation systems. A high dew point is a critical indicator of air quality that can lead to moisture condensation in pneumatic systems, pipelines and process equipment. This, in turn, causes corrosion, tool damage, product contamination, and automation malfunctions.

Symptoms to consider:

• High dew point values exceeding the established norms (for example, +3°C for refrigerator dryers).
• The presence of visible moisture or condensation in pipelines, filters, receivers or final devices of compressed air consumption.
• Premature failure of pneumatic equipment, valves or cylinders due to corrosion or leaching of lubricant.
• Product quality issues in moisture-sensitive processes (e.g. dyeing, packaging, pharmaceuticals).

Equipment types:

The manual focuses on refrigerated compressed air dryers, which are the most common in the industry to achieve a dew point of +2°C to +10°C. Diagnostic methods are applicable to both cyclic and non-cyclic models of dehumidifiers.

Classification of severity:

• Critical: Immediate risk of equipment damage, production stoppage, or significant impact on product quality. Requires immediate intervention.
• Significant: Reduced system performance, increased maintenance costs, potential failures that could lead to downtime. It needs to be eliminated as soon as possible.
• Minor: Periodic or minor deviations that do not affect critical processes, but indicate deterioration of the equipment and can develop into significant problems. Planned detection and elimination is recommended.

2. Precautions

CAUTION: Before starting any diagnostic or repair work on the compressed air dryer, it is necessary to strictly follow the safety rules. Failure to follow these instructions could result in serious injury or death.

Isolation of Power Sources (LOTO): Before opening any panels or accessing internal components, MUST disconnect electrical power to the dehumidifier and lockout/tagout in accordance with DSTU standards EN 10325 and internal plant procedures.

Releasing stored energy: Completely depressurize the compressed air system before working on air lines. Use safety valves and drain plugs. Check the absence of pressure using pressure gauges.

Working with refrigerants: Refrigerants are under high pressure and can cause frostbite in contact with the skin and eyes. Use personal protective equipment: safety glasses (EN 166), chemically resistant gloves (EN 374) and protective clothing. Avoid inhaling refrigerant vapors. Work with the refrigerant should be performed only by certified personnel in accordance with CE and UkrSEPRO requirements.

High temperatures: The components of the compressor part and hot line of the dryer can have high temperatures. Always allow equipment to cool before servicing.

Electrical safety: Any work with electrical components must be performed by a qualified electrician. Check the absence of voltage with a multimeter.

3. Necessary diagnostic tools

The following set of tools is required for accurate diagnosis of compressed air dryer malfunctions:

4. Initial evaluation checklist

Before starting a detailed diagnosis, it is necessary to conduct an initial examination and collect information. This will help narrow down the potential causes of the malfunction.

5. Systematic diagnostic algorithm

This algorithm will help to consistently determine the root cause of exceeding the dew point.

1. Exceeding the dew point at the outlet of the dehumidifier (> +3°C):
   1. Checking the electrical supply and operation of the refrigerant compressor:
      • If the compressor does not start:
      • Check the supply voltage and fuses with a multimeter. (<strong>ATTENTION: Live work should only be performed by a qualified electrician!</strong>) Expected result: 380V ±10%.
      • Check the pressure switch (high/low) - whether they have worked. Measure the contact resistance. Expected result: closed (for normal operation).
      • Check the start capacitor and compressor windings. Expected result: Winding resistance according to specification, capacitor capacity within tolerance.
      • If the compressor starts but runs intermittently or makes noise:
      • Check the operating current of the compressor with pliers. Expected result: within the rated current. An excess indicates mechanical problems or excessive stress.
      • Listen for unusual noises (knocking, grinding). This may indicate mechanical wear.
   2. Evaluation of refrigerant parameters:
      • Connect pressure gauges to the service ports of the compressor.
      • If the suction pressure (low) is significantly lower than normal (for example, < 2 bar for R-134a at +3°C evaporation):
        1. Probable cause: Insufficient amount of refrigerant (leakage) or partial blockage of the TRV (thermoregulation valve).
        2. Diagnosis:
           • Use an electronic refrigerant leak detector to search for leaks in all connections, heat exchangers, compressor seals.
           • Check the temperature of the pipelines before and after the TRV. A significant temperature difference may indicate clogging.
      • If the discharge pressure (high) is significantly higher than normal (eg > 18 bar for R-134a):
        1. Probable cause: Excess refrigerant, condenser clogging, condenser fan malfunction or high ambient temperature.
        2. Diagnostics:
           • Check the cleanliness of the condenser fins (visually).
           • Check the operation of the condenser fan (revolutions, power supply).
           • Measure the temperature at the inlet and outlet of the condenser.
   3. Checking heat exchangers:
      • Measure the temperature of the compressed air at the entrance to the cooling circuit of the dryer.
      • Measure the temperature of the compressed air at the outlet of the cooling circuit of the dryer (in front of the condensate separator). Expected result: The temperature should be around +3°C. If it is significantly higher, the heat exchanger is not working efficiently.
      • Check the surface temperature of the refrigerant heat exchanger (evaporator) with an infrared pyrometer. Expected result: Uniformly low temperature, without icing zones (icing indicates insufficient heat exchange or problems with the refrigerant).
      • Visually assess the external cleanliness of heat exchanger fins (evaporator and condenser).
      • Measure the pressure drop of the compressed air through the heat exchangers. Expected result: drop no more than 0.2 bar. A larger difference indicates internal clogging (oil, particles).
   4. Drain valve diagnostics:
      • Visually observe the operation of the valve.
      • If the drain valve is constantly open (continuous air leakage):
        1. Probable cause: Mechanical blockage, worn seals, solenoid valve or controller failure.
        2. Diagnosis: Turn off the air supply, disassemble the valve, check for foreign particles, wear of seals. Check the electrical signal on the solenoid coil.
      • If the drain valve does not open (condensate does not drain):
        1. Probable cause: Discharge hole blockage, solenoid valve failure, controller failure or no signal.
        2. Diagnosis: Check the electrical signal on the coil. Try to open manually (if provided). Check the presence of condensate in the separator.
   5. Assessment of compliance with the load:
      • Compare the actual parameters of the inlet air (pressure, temperature, flow rate) with the nominal characteristics of the dehumidifier.
      • If the inlet air temperature exceeds +45°C or the pressure is below 6 bar:
        1. Probable cause: Dehumidifier overload due to inconsistency in the parameters of the compressor station or a change in the technological process.
        2. Diagnostics: Check the passport data of the dehumidifier and compare with real operating conditions. Assess the presence of sufficient volume of the receiver to stabilize the load.
      • If the air consumption exceeds the nominal capacity of the dehumidifier:
        1. Probable cause: System overload.
        2. Diagnosis: Measure the actual air flow at the entrance to the dehumidifier.
      • For cycle dehumidifiers: If the dehumidifier turns on/off frequently or runs continuously:
      1. Probable cause: Load mismatch. Too frequent cycles indicate too much performance of the dehumidifier, continuous operation - insufficient.
      2. Diagnostics: Analyze the cycles of the dehumidifier according to the controller logs.

6. Matrix of malfunctions and causes

This table presents the likely causes of malfunctions, ranked by probability, diagnostic tests, and expected results.

7. Root cause analysis for each malfunction

7.1. Problems with the amount of refrigerant

Insufficient amount of refrigerant (underfilling/leakage)

• Why this happens: Over time, even the smallest leaks can lead to refrigerant loss. Leaks often occur at joints, compressor shaft seals, or through microcracks in pipelines and heat exchangers. An insufficient level of refrigerant leads to a decrease in the heat-absorbing capacity of the system.
• How to confirm: Low refrigerant suction pressure (<2 bar for R-134a) and increased suction superheat (+8-12°C above saturation temperature). Partial icing of the evaporator or TRV is often observed. The use of an electronic refrigerant leak detector is critical to accurately locating the leak.
• What damage does it cause: Reduced dehumidification efficiency, overheating of the compressor due to insufficient cooling of its motor by the refrigerant flow, increased wear of the moving parts of the compressor and potential failure of the compressor.

Excess refrigerant (refilling)

• Why this happens: Usually the result of improper charging of the system, when too much refrigerant is added.
• How to confirm: High refrigerant injection pressure (>18 bar for R-134a) and low or negative liquid supercooling at the condenser outlet. The compressor works with increased load.
• What damage it causes: An increase in pressure in the system can cause high-pressure safety relays to trip, compressor malfunctions, and excessive stress on electrical components.

7.2. Contamination of the heat exchanger

Internal contamination (air side)

• Why this happens: The air circuit of the dehumidifier can become contaminated with oil, dust and other particles that come with the compressed air if there is no or ineffective pre-filtration system. This creates an insulating layer on the internal surfaces of the heat exchanger, preventing efficient heat transfer.
• How to confirm: Increased pressure drop of compressed air through the heat exchanger (exceeds 0.3 bar). The temperature of the air at the outlet of the evaporator is increased, despite the normal parameters of the refrigerant.
• What damage does it cause: Decreased heat exchange efficiency, increased dew point, increased load on the refrigerant compressor, and potential clogging of the heat exchanger channels, requiring its replacement.

External contamination (air side of the condenser)

• Why this happens: Dust, dirt, fibers and other environmental contaminants can settle on the fins of the condenser, reducing its ability to dissipate heat to the atmosphere.
• How to confirm: High refrigerant injection pressure. A visual inspection shows clogging of the condenser fins. The temperature of the air leaving the condenser is much higher than the ambient temperature.
• What damages it causes: Refrigerant compressor overload, frequent activation of high pressure protection, reduction of dryer efficiency and shortening of compressor life.

7.3. Malfunction of the drain valve

The valve is always open

• Why this happens: Mechanical wear of the seals, foreign particles getting under the valve seat or malfunction of the electromagnetic drive.
• How to confirm: Constant leakage of compressed air from the drain, accompanied by a characteristic noise. Increased compressor energy consumption due to air loss.
• What damage it causes: Constant loss of compressed air, which leads to significant energy losses and increased load on the air compressor. It can also lead to unstable pressure in the system.

The valve is permanently closed

• Why this happens: Clogging of the exhaust channel, malfunction of the electromagnetic drive (broken winding, jamming of the rod) or a failure in the controller that controls its operation.
• How to confirm: No condensate discharge during the cycle. The presence of visible moisture in the drain pipes of the dryer. Checking the electrical signal on the valve coil with a multimeter.
• What damage is caused by: Condensation accumulation in the dryer, its subsequent entry into the compressed air system, which directly leads to a high dew point, corrosion and damage to pneumatic equipment.

7.4. Load mismatch

Dehumidifier overload

• Why this happens: If the actual consumption of compressed air, its inlet temperature or pressure exceeds the nominal values for which the dryer was designed. This may be the result of increasing production capacity without upgrading the air conditioning system, or extremely high ambient temperatures.
• How to confirm: Comparison of actual parameters (consumption, temperature, pressure) with passport data of the dehumidifier. The air temperature at the outlet of the dehumidifier is constantly higher than the target dew point, despite the correct operation of the refrigerant.
• What damage does it cause: Constantly high dew point, which leads to all the consequences of having moisture in the system. It also causes an increased load on all components of the dehumidifier, shortening their service life.

8. Step-by-step troubleshooting procedures

8.1. Restoring the normal amount of refrigerant

The refueling procedure should be performed only by a certified specialist.

1. CAUTION: Before starting work with the refrigerant, provide LOTO and wear personal protective equipment (safety glasses, chemically resistant gloves).
2. Detect and repair the leak: Using an electronic detector, locate and repair the leak (replace seals, solder, tighten connections).
3. Vacuuming the system: Connect the vacuum pump to the service ports. Pump out air and moisture to a residual pressure of no more than 0.3 mbar (250 microns of mercury) within 30-60 minutes. Hold the vacuum for 15 minutes without increasing the pressure.
4. Refrigerant charging: Connect a cylinder with a suitable refrigerant (e.g. R-134a) to the service port. Fill according to the nameplate of the dehumidifier (for example, 1.5 kg ± 50 g). Refuel in the liquid phase through the high-pressure line or in the gaseous phase through the suction line (with a slow feed to avoid hydraulic shock of the compressor).
5. Checking the operating parameters: Start the dehumidifier. Control the refrigerant suction and discharge pressure, outlet air temperature and dew point. Bring the suction pressure to 3.5-4.5 bar for R-134a at an evaporation temperature of +3°C. Superheat on suction should be 4-7°C.

8.2. Cleaning of heat exchangers

External cleaning of the condenser

1. CAUTION: Turn off power to dehumidifier (LOTO).
2. Remove large dirt: Use a soft brush or vacuum cleaner to remove dust and cobwebs from the condenser fins.
3. Washing: Carefully wash the fins of the condenser with compressed air (pressure up to 4 bar) or water under low pressure (using special detergents for air conditioners, if the contamination is strong). Rinse against the direction of air flow.
4. Drying: Ensure that the condenser is completely dry before starting the dryer.

Internal cleaning of the air-air heat exchanger (for oil contamination)

1. CAUTION: Disconnect power to dehumidifier (LOTO) and release air pressure.
2. Dismantling: Disconnect and, if necessary, dismantle the heat exchanger from the dryer.
3. Flushing: Flush the heat exchanger with special solvents for cleaning oil, strictly following the solvent manufacturer's instructions. Ensure complete removal of solvent and oil residues.
4. Drying: Thoroughly dry the heat exchanger with compressed nitrogen or dry air.
5. Installation: Install the heat exchanger in place, check the tightness of the connections.
6. Verification: After start-up, check the air pressure drop across the heat exchanger (must be <0.2 bar) and the dew point.

8.3. Replacement or repair of the drain valve

1. CAUTION: Disconnect power to dehumidifier (LOTO) and release air pressure.
2. Dismantling: Disconnect the electrical wires and dismantle the faulty drain valve.
3. Inspection: Carefully inspect the valve seat and seal for wear or obstruction. For valves with a float - check its mobility.
4. Cleaning/Replacement: If the valve is clogged, clean it. If there is wear or malfunction of the electric coil, replace the valve or its components with original spare parts.
5. Installation: Install new/repaired valve, connect electrical connections. Make sure the valve is installed in the correct position.
6. Adjustment and verification: After starting the dryer, check the valve cycle. For electronic valves, check the opening and closing time settings (eg 3-5 second opening every 3-5 minutes). Make sure that the condensate is completely discharged without excessive air loss.

8.4. Correction of load mismatch

1. System Audit: Perform a complete audit of the compressed air system, including measurements of actual air flow, dryer inlet temperature, and pressure.
2. Consideration of options:
   • If the overload is temporary, consider installing an additional receiver to stabilize the load.
   • If the overload is constant due to increased consumption, consider upgrading the air conditioning system: installing a higher performance dehumidifier or an additional dehumidifier in parallel.
   • Installing an air pre-cooler can lower the temperature of the air entering the dehumidifier, reducing its load.
3. Dehumidifier settings (for cycle models): Check hysteresis settings and duty cycle time to ensure optimal cooling without excessive on/off cycles.
4. Verification: After adjustment, perform long-term monitoring of the dew point and operating parameters of the dehumidifier.

9. Preventive measures

Regular maintenance is key to preventing the dew point from exceeding.

10. Spare parts and components

It is recommended to have the following spare parts available for quick elimination of typical malfunctions. All components can be found in the UNITEC-D electronic catalog at the link: https://www.unitecd.com/e-catalog/

To order or consult spare parts, please refer to the UNITEC-D e-catalogue: www.unitecd.com/e-catalog/

11. Links

• DSTU ISO 8573-1:2018 (ISO 8573-1:2010, IDT): Compressed air. Part 1: Classes of purity. This standard specifies requirements for compressed air quality, including dew point.
• DSTU EN 378 (series): Refrigeration systems and heat pumps. Safety and environmental requirements. Regulates requirements for the design, production, installation, maintenance and disposal of refrigeration systems.
• Operating and maintenance instructions from the dehumidifier manufacturer: Always refer to the original documentation for specific model parameters.
• Manuals for the maintenance of refrigeration equipment: General recommendations for working with refrigerants and refrigeration circuits.
• Accompanied UNITEC-D maintenance manuals: Other manuals related to compressor stations and filtration systems.