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Low superheat, floodback, suction line sweating/frosting to compressor, compressor knock
What is going on
Possible causes and checks for: low superheat, floodback, suction line sweating/frosting to compressor, compressor knock.
Likely causes
- Superheat set too low
- Oversized valve (hunting)
- Bulb picking up warm air (not insulated / bad contact → reads warm → overfeeds)
- Valve stuck open or leaking seat
- Pin/seat damaged by debris
Check in this order
- Superheat
- Hunting pattern over time
- Bulb contact/insulation
- External equalizer
- Close the valve and see if flow stops (off-cycle frost at start-up indicates leak-through)
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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.