Charging a system with the right amount of refrigerant is essential for performance and reliability. There are several recognised methods, and choosing the right one depends on the system type.
Charging by weight
The most accurate method for many systems: evacuate fully, then weigh in the exact charge specified by the manufacturer (adjusting for pipe-run length where required). Ideal for split systems and sealed units with a known charge.
Charging by superheat
Used on fixed-orifice (capillary) systems. You add refrigerant to achieve the target superheat for the operating conditions, often using a charging chart.
Charging by subcooling
Used on systems with a thermostatic expansion valve (TXV/TEV). You charge to the manufacturer’s target subcooling, which indicates the correct liquid charge.
Important practical points
- Always charge zeotropic blends as a liquid (from an upright cylinder) to keep the blend composition correct
- Evacuate to remove air and moisture before charging
- Verify the final charge with superheat and subcooling readings
FAQ
Should I charge refrigerant as liquid or vapour? Blends must be charged as liquid to avoid fractionation; single-component refrigerants are more forgiving, but always follow best practice.
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