Compressor Liquid Slugging — Liquid Refrigerant Ingestion
A field reference for compressor 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
- Suction superheat 0–3°C (normal 4–8°C)
- Suction line frost/heavy condensation
- Compressor body cool during off (liquid pooled)
- Startup knocking sound
- Liquid trace in suction line
Root causes
- TXV overfeeding — superheat too low
- Off-cycle liquid migration — crankcase heater not working
- Startup liquid ingestion — no/inadequate accumulator
- TXV stuck open
- Bulb fell off
- Refrigerant overcharge
If you leave it unrepaired
- Incompressible liquid → instant destructive impact
- Discharge reed valve breaks → 50%+ efficiency drop
- Connecting rod bend/break → stop
- Oil pump damage → bearing wear
- Even mild slugging cuts bearing life to 1/4
How to fix it
- Adjust TXV superheat to 4–8°C
- Verify bulb position/insulation
- Verify crankcase heater operation
- Install/upgrade accumulator
- Check refrigerant charge
- Existing damage: inspect valves/bearings → replace decision
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What causes compressor liquid slugging — liquid refrigerant ingestion?
TXV overfeeding — superheat too low Off-cycle liquid migration — crankcase heater not working Startup liquid ingestion — no/inadequate accumulator TXV stuck open Bulb fell off Refrigerant overcharge
How do I diagnose compressor liquid slugging — liquid refrigerant ingestion on site?
Suction superheat 0–3°C (normal 4–8°C) Suction line frost/heavy condensation Compressor body cool during off (liquid pooled) Startup knocking sound Liquid trace in suction line
How do I fix compressor liquid slugging — liquid refrigerant ingestion?
Adjust TXV superheat to 4–8°C Verify bulb position/insulation Verify crankcase heater operation Install/upgrade accumulator Check refrigerant charge Existing damage: inspect valves/bearings → replace decision
What happens if compressor liquid slugging — liquid refrigerant ingestion is left unrepaired?
Incompressible liquid → instant destructive impact Discharge reed valve breaks → 50%+ efficiency drop Connecting rod bend/break → stop Oil pump damage → bearing wear Even mild slugging cuts bearing life to 1/4