Diagnostics and Troubleshooting Guide: Dew Point Deviation in Compressed Air Dryers

1. Description of the problem and scope of application

This manual is intended for diagnosing and troubleshooting problems associated with abnormally high outlet dew points from refrigerated compressed air dryers. A high dew point indicates the presence of an excessive amount of moisture in the compressed air, which is a critical violation of its quality. Consequences include corrosion of pneumatic equipment, clogging of pipelines, damage to tools, reduced efficiency of production processes, and deterioration of end products, especially in the pharmaceutical, food and chemical industries. This is a critical fault that requires immediate attention to prevent significant production losses and costly equipment repairs.

Field of application: Compressed air refrigerating dryers with direct cooling or cooling with the help of an air-to-air and air-to-refrigerant heat exchanger. The guide covers the following primary causes: insufficient refrigerant charge, heat exchanger contamination, drain valve failure, and load mismatch.

2. Safety measures

ATTENTION! All diagnostic and repair work must be performed by qualified personnel in accordance with DSTU EN ISO 10218-1:2020 and local labor safety regulations.

LOCKOUT/DISABLE! Before starting any work that requires access to the internal components of the dehumidifier or electrical systems, it is necessary to completely de-energize the equipment and apply the lockout/disarm (LOTO) procedures in accordance with DSTU EN 1037:2003.

COMPRESSED AIR AND REFRIGERANT! Compressed air and refrigerant systems are under high pressure. Risk of injury or rupture. Never disconnect components until the system is completely depressurized. Refrigerants can cause frostbite on skin contact and are dangerous if inhaled. Always use personal protective equipment (PPE): safety glasses, gloves, overalls.

ELECTRICAL HAZARD! Dehumidifier components contain dangerous voltage. Before working with electrical parts, make sure that the power is turned off and check that there is no voltage with a multimeter.

3. Necessary diagnostic tools

4. Initial evaluation checklist

5. Systematic diagnostic algorithm

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

1. Initial symptom: High dew point at the outlet of the dehumidifier (> +3°C for refrigerators)

   1. Does the dehumidifier work?

      • IF NOT:
        1. Check the power supply of the dehumidifier (input voltage 380V ±10% / 230V ±10%).
        2. Check fuses and circuit breakers.
        3. Check the control panel for alarms.
        4. PROBABLE CAUSE: No power or alarm.
        5. GO TO: Section 8 (General Power Recovery Procedures).
      • IF YES: Continue diagnostics.

   2. Is the refrigerant compressor working?

      • IF NO:
        1. Check compressor relay/contactor.
        2. Check thermostats and pressure switches (low/high pressure) - are they working?
        3. Check the compressor supply voltage (measure at the terminals).
        4. PROBABLE CAUSE: Compressor electrical problems, tripping of protection (low/high pressure, overheating).
        5. GO TO: Section 6, line "Refrigerant compressor not running".
      • IF YES: Continue diagnostics.

   3. What are the refrigerant pressures (suction/discharge)? (Measure with refrigerant manifold pressure gauges)

      • Typical values for R134a at evaporation temperature +3°C and condensation temperature +40°C:
        • Suction pressure: 2.8 – 3.2 bar (for evaporation temperature +3°C)
        • Discharge pressure: 10.0 – 11.5 bar (for condensation temperature +40°C)
      • IF suction pressure is SIGNIFICANTLY LOW (< 1.5 bar) and/or discharge pressure is LOW (< 8 bar):
        1. Check for frost/freeze on the suction line (usually a low pressure indicator).
        2. Use a refrigerant leak detector throughout the circuit.
        3. PROBABLE CAUSE: Insufficient refrigerant charge due to leakage.
        4. GO TO: Section 7 (Insufficient Refrigerant Charge).
      • IF the delivery pressure is MUCH HIGHER (> 12.5 bar) and/or the suction pressure is HIGHER (> 4.0 bar):
        1. Check the cleanliness of the condenser (dust contamination).
        2. Check the operation of the condenser fan (is it rotating or not blocked).
        3. Measure the temperature of the air leaving the condenser (it should be hot).
        4. PROBABLE CAUSE: Condenser contamination or fan malfunction.
        5. GO TO: Section 7 (Heat Exchanger Fouling: Condenser).
      • IF the pressures appear within normal limits, but the dew point is high:

   4. Does the condensate drain effectively?

      • Visually check the operation of the drain valve.

        1. Listen for the characteristic reset sounds.
        2. Check if the drain valve is constantly leaking (air leakage).
        3. Collect condensate over a period of time (e.g. 10 minutes) - does it correspond to the expected amount?
      • IF the drain valve does not drain, drains constantly, or is blocked:
        1. PROBABLE CAUSE: Drain valve failure (blocked, defective).
        2. GO TO: Section 7 (Drain Valve Failure).
      • IF the drain valve is working correctly: Continue diagnostics.

   5. What are the temperatures at the inlet and outlet of the "air-refrigerant" heat exchanger?

      • Measure the air temperature at the entrance to the heat exchanger of the dryer.
      • Measure the air temperature at the outlet of the heat exchanger of the dryer.
      • Measure the surface temperature of the heat exchanger with a thermal imaging camera.
      • Expected difference: The outlet temperature should be 2-3°C higher than the refrigerant evaporation temperature.
      • IF THE TEMPERATURE DIFFERENCE IS SMALL OR THE SURFACE OF THE HEAT EXCHANGER HAS A NON-HOGENEOUS TEMPERATURE DISTRIBUTION:
        1. PROBABLE CAUSE: Contamination of the heat exchanger (from the air side).
        2. GO TO: Section 7 (Heat Exchanger Fouling: Air Side).
      • IF all the previous items are normal, but the dew point is high:

   6. Does the load of the dehumidifier correspond to its design capacity?

      • Compare the current compressed air flow with the maximum capacity of the dehumidifier.
      • Check that there are no significant load fluctuations (periodic peaks).
      • Compare the inlet air and ambient temperature with the dehumidifier's data sheet.
      • IF the load exceeds the nominal parameters or there are significant fluctuations:
        1. PROBABLE CAUSE: Load mismatch (overload, incorrect selection).
        2. GO TO: Section 7 (Load Mismatch).

6. Matrix of malfunctions and causes

7. Root cause analysis for each malfunction

7.1. Insufficient refrigerant charge

Explanation: A reduction in the amount of refrigerant in the system is usually caused by leaks through connections, seals, or microcracks in piping or components. Refrigerant is a working fluid that absorbs heat from the air in the evaporator heat exchanger. If there is an insufficient amount, its cooling capacity decreases, which leads to inefficient cooling of compressed air.

How to confirm:

• Measure the refrigerant suction and discharge pressure. With insufficient charge, both pressures will be lower than normal, especially the suction pressure (can drop to negative values).
• Check for frost or ice on the suction line or on the evaporator.
• Use an electronic refrigerant leak detector (sensitivity from 3 g/year) to pinpoint the location of the leak.

Damage if left unaddressed: Persistently high dew point causing corrosion and damage to pneumatic equipment. Overheating and failure of the refrigerant compressor is possible due to the lack of proper cooling of its engine with refrigerant.

7.2. Contamination of the heat exchanger

Explanation: Heat exchangers (condenser and evaporator) play a key role in the cooling process. The condenser dissipates the heat of the refrigerant into the environment, and the evaporator absorbs heat from the compressed air. Contamination of the outer surfaces of the ribs (dust, oil, dirt) or the inner surfaces (scaling, deposits) creates a thermal barrier that prevents effective heat exchange. This leads to an increase in condensation pressure and evaporation temperature.

How to confirm:

• Condenser (air side): Visual inspection. Use a thermal imaging camera - contaminated areas will be colder. Measure the air temperature difference at the inlet/outlet of the condenser - in case of contamination, the difference will be smaller than normal.
• Evaporator (air side): Visual inspection (sometimes possible). Measure the surface temperature of the evaporator with a thermal imaging camera - non-uniform temperatures may indicate internal contamination or partial blockage.

Unfortunate if left unsolved: Refrigerant compressor overload, which leads to its overheating and premature wear. Increased electricity consumption. Constantly high dew point.

7.3. Drain valve failure

Explanation: The drain valve is responsible for draining the condensate formed in the dryer. If the valve is locked in the closed position, condensate accumulates in the evaporator, reducing the effective heat transfer area and preventing further condensation. If the valve is stuck in the open position, it results in a constant loss of compressed air, reducing system pressure and increasing the load on the air compressor.

How to confirm:

• Valve blocked (closed): No condensate discharge during the operating cycle. Flooding of the evaporator is possible.
• Valve blocked (open) or faulty (leaking): Constant flow of air from the drain, even when condensate does not drain. Measure air loss (you can use an ultrasonic leak tester).
• Manual test: If the valve has a manual opening button, check that it opens and drains condensate.

It would be a shame if left unsolved: Moisture accumulation in the compressed air system. Significant loss of compressed air and increased energy costs for the air compressor. Dehumidifier overload and subsequent damage is possible.

7.4. Load mismatch

Explanation: The compressed air dryer is designed for a certain maximum performance (air consumption, inlet air temperature, ambient temperature). If any of these parameters consistently exceeds the design values, the dehumidifier will not be able to provide the desired dew point. This may be the result of increased production needs without upgrading the dryer, changing operating conditions, or incorrect initial selection of equipment.

How to confirm:

• Compare the current average and peak compressed air flow (as measured by the air meter) with the dehumidifier's rated capacity.
• Measure the temperature of the incoming compressed air.
• Measure the ambient temperature.
• Compare all measured parameters with the passport data of the dehumidifier.

Unfortunate if left unsolved: Constantly high dew point, despite all components being in good working order. Increased energy consumption. Reduction of the service life of the dehumidifier due to constant operation in overload conditions.

8. Step-by-step troubleshooting procedures

8.1. Refrigerant charge recovery

1. SECURITY: Apply LOTO procedures. Put on PPE (safety glasses, gloves, overalls).
2. Identify and repair refrigerant leaks with an electronic detector. Replace damaged components or seals.
3. Pump the residual refrigerant from the system into a special cylinder for recovery.
4. Deep vacuum the system to a pressure of no more than 0.3 mbar (225 microns Hg) and hold for 30 minutes to remove moisture and non-condensable gases.
5. Charge the system with new refrigerant (same type as specified on the dehumidifier nameplate) to the nominal weight (e.g. 1.2 kg for R134a) or until the refrigerant's nominal pressures are reached at operating temperature.
6. Start the dryer, check pressures and temperatures. Make sure the dew point has stabilized at +3°C ±1°C.

8.2. Cleaning the heat exchanger

1. SECURITY: Apply LOTO procedures. Put on PPE. Provide adequate ventilation.
2. Cleaning the Condenser (Air Side):
   1. Remove covers and access panels.
   2. Use compressed air (no more than 3 bar oil-free) or a soft brush to gently remove dust and dirt from the fins. The direction of cleaning is opposite to the direction of the air flow during operation.
   3. For heavy contamination, use special detergents for cleaning heat exchangers that do not cause aluminum corrosion, according to the manufacturer's instructions. Rinse thoroughly with clean water after use.
3. Evaporator (air side) and air-to-air heat exchanger cleaning:
   1. Follow the dehumidifier manufacturer's instructions as access to these heat exchangers may be restricted.
   2. Usually, washing with special means or careful blowing with air is used.
4. After cleaning, replace the panels, restore power and test the dehumidifier.

8.3. Drain valve repair/replacement

1. SECURITY: Apply LOTO procedures. Unplug the dehumidifier. Depressurize the compressed air system.
2. If the valve is blocked, try to clean it. Unscrew the valve body, check for dirt, rust or foreign particles.
3. Clean all valve components using an appropriate solvent or cleaner. Check the seal for damage.
4. If the valve is electric, check its solenoid coil with a multimeter for resistance (should match the manufacturer's data, usually 500-1500 ohms). Check the voltage applied to the coil.
5. If cleaning and electrical checks do not help, replace the drain valve with a new one that matches the specifications (size, type, voltage, material).
6. After replacement/maintenance, restore air pressure, power and check valve operation (regular reset, no constant air leaks).

8.4. Correction of load mismatch

1. Score: Accurately determine current average and peak air flow, inlet air temperature and ambient temperature.
2. Analysis: Compare these data with the passport data of the dehumidifier. If the available parameters constantly exceed the nominal ones, there are several options:
1. Load Reduction: Review the process of using compressed air to identify and eliminate unnecessary costs (such as distribution system leaks).
2. Improving operating conditions: Provide better ventilation in the room where the dehumidifier is installed to reduce the ambient temperature. Install an after-cooler after the compressor if the intake air temperature is excessive.
3. Upgrade: If load reduction or improvement is not possible, consider replacing the dehumidifier with a higher performance model that meets current needs.
3. After implementing changes, regularly monitor dew point and load parameters to confirm effectiveness.

9. Precautions

10. Spare parts and components

More spare parts and components can be found in our e-catalog: https://www.unitecd.com/e-catalog/

11. Links

• DSTU EN 1037:2003 (EN 1037:1995, IDT) Machine safety. Prevention of unexpected start.
• DSTU EN ISO 10218-1:2020 (EN ISO 10218-1:2011, IDT; ISO 10218-1:2011, IDT) Robotic systems for the industrial environment. Security requirements.
• ISO 8573-1:2010 Compressed air. Part 1: Contaminants and purity classes.
• Operation and maintenance manuals from OEM dehumidifier manufacturers (eg Atlas Copco, Parker, SMC).
• Relevant sections of the UNITEC-D service manuals.