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Flash gas in liquid line (bubbles in sight glass with full charge) / frost-back on suction
What is going on
Possible causes and checks for: flash gas in liquid line (bubbles in sight glass with full charge) / frost-back on suction.
Likely causes
- Warm liquid line, no subcooling, SLHX missing or piped parallel-flow
Check in this order
- Liquid line temperature vs saturation, SLHX piping counterflow
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Source: General HVAC service practice — verify per model. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.