Diagnostic Guide: Dew Point Excursions on Compressed Air Dryers

1. Description and Scope

This guide covers unexpected increases in pressure dew point (PDP) on refrigeration compressed air dryers. An excursion of the dew point (beyond the nominal limit of 3°C, class ISO 8573-1: 4) indicates a failure of the heat exchange capacity or the evacuation of condensates. In the aerospace and energy industry, this residual moisture causes precision pneumatic components to corrode, control ports to clog, and instrumentation systems to fail. Severity classification: Critical.

2. Safety Precautions

WARNING: ELECTRICAL AND MECHANICAL HAZARD. Before any intervention, isolate the dryer from the power supply (LOTO padlock/tagout). The refrigeration circuit contains fluids under high pressure. Never open the refrigeration circuit without prior recovery by a certified technician. Wear personal protective equipment (fluid-resistant gloves, safety glasses) to avoid cryogenic burns and acid condensate splashes.

3. Required Diagnostic Tools

4. Initial Assessment Checklist

5. Systematic Diagnostic Flow

1. Symptom: Dew point alarm activated (> 5°C)
   1. Step 1: Check the condensate drain.
      Observe the purge cycle. If no condensate is discharged despite the presence of air, the drain is blocked.
      Result A: Faulty drain -> Replace or repair the drain kit.
      Result B: Functional drain -> Go to step 2.
   2. Step 2: Inspection of the condenser (air/ambient exchanger).
      Use the thermal camera to identify uniform hot spots or cold areas. High temperature across entire coil indicates dust clogging or fan failure.
      Result A: Clogged -> Clean with compressed air or dry steam.
      Result B: Fan inoperative -> Check motor and start-up capacitor.
      Result C : Clean exchanger -> Go to step 3.
   3. Step 3: Analysis of the refrigeration circuit (temperatures and pressures).
      Measure the suction and discharge temperature of the refrigeration compressor.
      Result A: Abnormally low suction pressure -> Probable fluid leak or obstructed expansion valve.
      Result B: Stable temperatures -> Go to step 4.
   4. Step 4: Checking the workload.
      Compare the actual compressed air flow with the rated capacity of the dryer. A dryer undersized for the current load will not be able to maintain the PDP.
      Result A: Overload -> Offload or replace the dryer.

6. Symptoms-Causes Matrix

7. Root Cause Analysis

A. Automatic drain failure

The most common cause is the accumulation of oily residue or particles in the drain tank. If the drain does not open, condensate accumulates in the air/freon exchanger, causing water to be entrained in the outgoing air flow. This immediately causes a PDP excursion.

B. Clogging of the heat exchanger

Fouling reduces the heat transfer coefficient. The air/refrigerant exchanger is no longer able to cool the air sufficiently to condense the humidity. The outlet air temperature is directly correlated to the refrigerant saturation temperature.

C. Refrigerant leak

A leak reduces the cooling capacity. The compressor is running, but the evaporator temperature is not dropping low enough. This is a critical cause because it leads to a gradual degradation of performance.

8. Resolution Procedures

1. Drain Replacement (Example: Timed/Electronic Type)
   1. Isolate the pressure (close upstream/downstream valves). 2. Bleed residual pressure. 3. Disconnect the power supply. 4. Unscrew the entire drain. 5. Install the new seal/drain kit with tightening torque of 15 Nm. 6. Reopen the valves slowly.
2. Cleaning the exchanger
   1. Turn off the dryer. 2. Use compressed air at low pressure (< 2 bar) in the opposite direction to the ambient air flow. 3. If very dirty, use a non-corrosive degreaser (type NF EN 1276). 4. Rinse with demineralized water. 5. Dry before returning to service.
3. Cooling Charge Procedure
   1. Carry out a leak test under nitrogen (dry nitrogen, 15 bar, 24 hours). 2. Draw a vacuum (< 500 microns). 3. Charge the refrigerant (type and quantity according to nameplate) in liquid phase.

9. Preventive Measures

10. Spare Parts (UNITEC-D)

To order these components, please consult our online catalog: https://www.unitecd.com/e-catalog/

11. References

• ISO 8573-1:2010 (Compressed air quality)
• NF EN 378 (Refrigerating systems)
• ATEX directives (if applicable to the installation)
• OEM Technical Manuals (Unitec-D X Series Dryers)