R-Pro › Field cases › Refrigerators & showcases
Zero Subcooling — Continuous Bubbles in Liquid Sight Glass
Likely causes
Severe undercharge — active leak in progress
Check: If sight glass shows continuous bubbles/flash gas with subcooling at 0°C and superheat over 20°C, an active leak is highly suspected. Document pressure drop rate per hour of operation.
What to do: 1) Stop immediately — continued operation overheats compressor and causes abnormal wear. 2) Trace leak — use electronic detector on condenser coil, flares, brazes, service valves. 3) On finding leak: recover → repair → evacuate 30 min → recharge by weight. 4) Photograph leak location for service history.
Condenser not fully flooded — non-condensable gas (NCG) or excess oil in condenser coil
Check: High-side pressure abnormally high + after shutdown, condensing pressure remains 0.5 MPa above ambient saturation → strong NCG suspicion. Possible causes: inadequate evacuation or air ingress after a leak.
What to do: 1) Recover all refrigerant. 2) Evacuate with vacuum pump to ≤500 microns (3+ hours, dual-stage pump recommended). 3) Hold vacuum 30 min — rise within 50 microns acceptable. 4) Recharge by weight. For excess oil, install oil separator or perform full system flush.
Bubbles do not always mean undercharge. Condenser blockage, NCG, drier restriction, and other liquid-line flow defects also produce bubbles. Always combine leak check with high-side pressure analysis.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
Open R-Pro →Related cases
- Abnormal Superheat — Low / High Diagnosis
- Superheat Hunting — TXV Oscillation
- Superheat Cannot Be Measured — Gauge or Thermometer Reliability Failure
- Abnormal Subcooling — Low / High Diagnosis
- PT Chart Usage — Pressure↔Temperature Conversion Diagnosis
- Refrigerant Type Cannot Be Identified — Missing Nameplate or Painted Over