1. Scope and Objective

This guide details preventative maintenance procedures for refrigeration compressed air dryers used in industrial facilities, particularly in the aerospace and energy sectors. The objective is to guarantee the quality of the compressed air (dew point compliant) and to ensure the longevity of the equipment. The procedures cover checking the refrigerant charge, testing the condensate trap and cleaning the heat exchanger.

WARNING: This guide is intended for use by qualified and authorized service technicians. Any intervention on the refrigeration circuit requires certification (capacity certificate) in compliance with current regulations (e.g. F-Gas Regulation in Europe).

2. Safety Precautions

DANGER: Before any intervention, apply the lockout procedure (Lockout/Tagout - LOTO) on the main power supply of the dryer.
DANGER: The refrigeration circuit is under pressure. Contact with refrigerant can cause severe frostbite or eye damage. Always wear safety glasses and insulated gloves.
CAUTION: Internal parts of the compressor can reach high temperatures. Allow the unit to cool before intervention.

3. Tools and Materials Required

Tool	Specification	Quantity
Refrigeration manifold	R134a/R407c compatible	1
Digital multimeter	True RMS, CAT III 600V	1
Torque wrench	Range 5-50 Nm	1
Winged comb	Pitch 12-16 fins/inch	1
Leak detector	Electronic (sensitivity 5g/year)	1
Industrial vacuum cleaner	With soft brush tip	1
PPE (gloves, glasses, shoes)	Standards EN 388, EN 166	1 game

4. Pre-Maintenance Checklist

Item	Verification	Criteria
Suction pressure	Pressure gauge/Display	In OEM range (bar)
Discharge pressure	Pressure gauge/Display	In OEM range (bar)
Drainage	Visualization	No permanent leak
Fan	Rotation	No abnormal noise
Leaks	Visual/Detector	No trace of oil

5. Step by Step Procedure

Preparation: Apply LOTO to the 400V/230V power supply. Wear required PPE. Remove the camber panels using a suitable screwdriver.
Checking the refrigerant:
- Connect the refrigeration manifold to the service connections (low and high pressure). Never force the connections.
- Check the pressures when stopped and in operation. Compare with nameplate.
- Check for superheating and subcooling. A value out of tolerance often indicates a lack of charge or a clogged exchanger.
- Look for traces of oil on the solder (leak indicator).
Cleaning the heat exchanger (Condenser):
- Dust the condenser fins with the vacuum cleaner. Do not use high pressure compressed air to avoid bending the fins.
- Use the fin comb to straighten distorted fins to restore nominal airflow.
Testing the condensate trap:
- Mechanically isolate the trap.
- Disassemble the purge valve, clean the seat and needle.
- Reassemble and perform a manual operating test by forcing the purge cycle. Check water drainage.

6. Post-Maintenance Checklist

Test	Expected result	Current	Pass/Fail
Circuit sealing	No leaks detected
Operating pressure	Plate compliant
Purge	Manual cycle validated
Temperatures	Stable (delta T)

7. Troubleshooting Guide

Symptom	Probable Cause	Corrective Action
High dew point	Dirty condenser / Lack of fluid	Clean condenser / Check for leak
Compressor does not start	Start relay / HS capacitor	Test with multimeter
Ice on the evaporator	Insufficient air flow	Check fan / Clean

8. Recommended Maintenance Schedule

Task	Frequency	Duration	Level
Condenser cleaning	Quarterly	30 mins	Technician
Trap test	Monthly	15 mins	Operator
Refrigerant charge control	Annual	60 mins	Expert

9. Spare Parts Reference

Description	Specification	Category
Trap Kit	Timed/Level	Dryer Accessories
Capacitor	Capacity/Voltage	Electrical Components
Fan	Flow/Voltage	Cooling

To order spare parts, please consult our e-catalog: https://www.unitecd.com/e-catalog/

10. References

NF standard EN 378-2 (Safety and environment of refrigeration systems)
Dryer OEM Documentation
F-Gas Regulation (EU) 517/2014