Filter Drier Moisture Saturated — Free Water in System
A field reference for filter drier faults — what causes it, how to confirm it on the unit, how to repair it, and what fails next if you leave it. Written for working HVAC & refrigeration technicians.
How to confirm it on site
- Moisture indicator yellow/pink (normal blue/green)
- TXV frost — warm cloth releases temporarily
- Oil TAN > 0.05 mgKOH/g
- Compressor winding insulation < 1MΩ
- Refrigerant moisture > 50 ppm
Root causes
- Insufficient vacuum (>500 micron or <30 min)
- Pipework left open without N2 purge
- Moisture-contaminated refrigerant
- Undersized drier
- Inadequate cleanup after burn-out
If you leave it unrepaired
- Drier exceeds moisture capacity → free water circulates
- TXV moisture freeze → flow blockage
- Acid formation — moisture + R-22 → HCl
- Acid attacks compressor winding → progressive burn-out
- Oil acidity rises → bearing wear
How to fix it
- Recover → vacuum ≤500 micron + Triple Evacuation (3x)
- Install larger or burn-out-specific drier
- Check oil TAN → replace if acidic
- Check winding insulation → replace compressor if damaged
- Standardize vacuum procedure + monitor moisture indicator
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What causes filter drier moisture saturated — free water in system?
Insufficient vacuum (>500 micron or <30 min) Pipework left open without N2 purge Moisture-contaminated refrigerant Undersized drier Inadequate cleanup after burn-out
How do I diagnose filter drier moisture saturated — free water in system on site?
Moisture indicator yellow/pink (normal blue/green) TXV frost — warm cloth releases temporarily Oil TAN > 0.05 mgKOH/g Compressor winding insulation < 1MΩ Refrigerant moisture > 50 ppm
How do I fix filter drier moisture saturated — free water in system?
Recover → vacuum ≤500 micron + Triple Evacuation (3x) Install larger or burn-out-specific drier Check oil TAN → replace if acidic Check winding insulation → replace compressor if damaged Standardize vacuum procedure + monitor moisture indicator
What happens if filter drier moisture saturated — free water in system is left unrepaired?
Drier exceeds moisture capacity → free water circulates TXV moisture freeze → flow blockage Acid formation — moisture + R-22 → HCl Acid attacks compressor winding → progressive burn-out Oil acidity rises → bearing wear