Restriction in the Refrigerant Circuit
Recognising a plugged drier, a kinked line or a failing metering device from the readings they produce.
Safety
Compressor: Low pressure vapor is compressed into hot, high pressure discharge gas.
Symptom
Symptom
Poor cooling with low suction pressure and high superheat, while subcooling is normal or high.
Symptom
A noticeable temperature drop, sweating or frost at one point in the liquid line.
Possible causes
- Plugged filter drier, often after a compressor failure or a system that was left open.
- Moisture freezing at the metering device, which comes and goes as the system cycles.
- Kinked or crushed liquid line.
- Metering device failing closed or partially blocked by debris.
- Closed or partially closed service valve after previous work.
What to check
Superheat and subcooling together
High superheat with high subcooling is the classic restriction signature. High superheat with low subcooling is undercharge instead
Temperature across the filter drier
A measurable drop, condensation or frost at the drier confirms a restriction there
Whether the problem is intermittent and clears after an off cycle
Strongly suggests moisture freezing at the metering device
The full length of the liquid line for kinks and damage
Mechanical damage is easy to miss behind equipment and at the line set entry
Service valve positions
A partially back seated or closed valve creates an artificial restriction
System history
A prior compressor failure or open system points to contamination and acid
Next step
- 1Recover the charge to an approved cylinder.
- 2Correct the mechanical cause, replacing the drier, metering device or damaged line as required.
- 3Pressure test with dry nitrogen and confirm the system holds.
- 4Evacuate to the target micron level and confirm the vacuum is stable.
- 5Weigh in the manufacturer specified charge and verify with superheat or subcooling.
- 6Record the readings so the next visit has a baseline.
Refrigerant handling
Symptoms
Practice & Mastery
- Restriction in the Refrigerant Circuit Troubleshooting Scenarios2
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