HVACopediaVacuum decay test
Leak or moisture? Read the micron rise after isolating the pump.
Good to know
- Deep vacuum method: pull to 250 microns, isolate the pump, and watch for one to three minutes.
- Triple evacuation: pull to about 1500 microns three times, breaking each with dry nitrogen to 0 to 3 psig.
More refrigeration calculators
Superheat (fixed orifice / cap tube)Actual superheat and the target from the outdoor and indoor temperaturesSubcooling (TXV systems)Subcooling from the head pressure and the liquid line tempRecovery cylinder max fillThe 80% rule: how much refrigerant a cylinder may holdVacuum pump sizePump size and vacuum targets by system sizeWalk-in cooler / freezer loadWall, door-air, product and extra heat loads; suggested capacityDefrost heater energykWh and heat added per day from the defrost cycles
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Calculation aids and reference figures for licensed technicians. Always follow the manufacturer’s data plate and manual for the exact model, and local codes. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Pressures are typical saturation values and change with load and airflow.