After a repair, why is a system evacuated with a vacuum pump before it is charged?
Dehydration and evacuation · EPA 608 Core. The correct answer, and the reasoning behind it.
Evacuating to remove air and moisture at the end of service.
The question
After a repair, why is a system evacuated with a vacuum pump before it is charged?
- To cool the compressor before startup
- To remove air and moisture from the systemCorrect answer
- To measure how much refrigerant leaked out
- To mix the new oil with the refrigerant
Why “To remove air and moisture from the system” is correct
Evacuation removes air (non-condensables) and moisture that entered while the system was open. Leaving them in causes high pressures, poor cooling, acid and sludge, so the system is evacuated before refrigerant is added.
Source: EPA: Test Topics
Why the other answers are wrong
- To cool the compressor before startup — Evacuation is not a cooling step for the compressor.
- To measure how much refrigerant leaked out — Leak amount is measured by recovery weight or charge records, not by evacuation.
- To mix the new oil with the refrigerant — Oil and refrigerant mix in operation; evacuation is about removing contaminants.
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