To change the compressor on a system containing R-410A, you must isolate the compressor then evacuate the isolated section of the system to ______ ______ and hold. If the system pressure does not rise, remove the compressor.

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When changing the compressor on an R-410A system, you want to be sure the section you’re working on is completely free of pressure before you disconnect the lines. The test concept here is to evacuate the isolated portion to atmospheric pressure and hold. This means bringing that isolated pocket of refrigerant down to ambient pressure so nothing in that section is pushing back into the compressor as you remove it.

Why this matters: if the isolated side is at atmospheric pressure and remains there, there’s no refrigerant under pressure in that pocket that could vent or blow out when you take the compressor out. If the pressure in that pocket rises during the hold period, it indicates there’s still refrigerant or a leak feeding into that isolated portion, and removing the compressor could release refrigerant unexpectedly. In that case, you’d stop and address the leak or the pressure buildup before proceeding.

Atmospheric pressure is the standard way to describe the condition you aim for in this step. Other ways of expressing the same idea, like a specific vacuum or a gauge pressure, would not reflect the procedure described here.