Filter Drier Blocked — Liquid Line ΔP Causes Starvation
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
- ΔT across drier ≥3°C (normal 0–1°C)
- ΔP > 0.5 bar abnormal
- Drier surface frost/condensation
- Sight glass bubbles increase
- Suction superheat rising
Root causes
- Moisture saturation — molecular sieve at limit
- Acid sludge after burn-out
- Debris accumulation — copper chips, flux
- Oil sludge — mineral oil oxidation
- Long service life without replacement
If you leave it unrepaired
- Pressure drop across drier (ΔP > 0.5 bar) → TXV inlet starved
- TXV hunting → superheat variation
- LP trip possible (partial blockage)
- Sight glass bubbles increase — flash gas in liquid line
- Capacity drops 30–50%
How to fix it
- Recover refrigerant → replace drier (same cu in size)
- Vacuum ≤500 micron for 30+ min
- If burn-out caused: full system flush + new oil
- Prevention: monitor with moisture indicator sight glass
- Replace every 5–10 years
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What causes filter drier blocked — liquid line δp causes starvation?
Moisture saturation — molecular sieve at limit Acid sludge after burn-out Debris accumulation — copper chips, flux Oil sludge — mineral oil oxidation Long service life without replacement
How do I diagnose filter drier blocked — liquid line δp causes starvation on site?
ΔT across drier ≥3°C (normal 0–1°C) ΔP > 0.5 bar abnormal Drier surface frost/condensation Sight glass bubbles increase Suction superheat rising
How do I fix filter drier blocked — liquid line δp causes starvation?
Recover refrigerant → replace drier (same cu in size) Vacuum ≤500 micron for 30+ min If burn-out caused: full system flush + new oil Prevention: monitor with moisture indicator sight glass Replace every 5–10 years
What happens if filter drier blocked — liquid line δp causes starvation is left unrepaired?
Pressure drop across drier (ΔP > 0.5 bar) → TXV inlet starved TXV hunting → superheat variation LP trip possible (partial blockage) Sight glass bubbles increase — flash gas in liquid line Capacity drops 30–50%