What usually causes the pressure to rise in an R-22 system that has just been pulled down to its recovery vacuum?
Recovery techniques · EPA 608 Type II. The correct answer, and the reasoning behind it.
Recovering liquid first, speeding recovery, and avoiding cross-contamination.
The question
What usually causes the pressure to rise in an R-22 system that has just been pulled down to its recovery vacuum?
- Refrigerant boiling out of the oil or remaining liquidCorrect answer
- Air leaking into the system through the gauge set hoses
- Heat from the recovery machine
- A failed pressure gauge
Why “Refrigerant boiling out of the oil or remaining liquid” is correct
Liquid refrigerant trapped in low spots, or refrigerant dissolved in the compressor oil, keeps boiling off after the machine stops. That vapor raises the pressure and must be recovered.
Source: EPA: Test Topics
Why the other answers are wrong
- Air leaking into the system through the gauge set hoses — A small air leak would not usually cause a quick, steady rise, and it is not what the check looks for.
- Heat from the recovery machine — The recovery machine does not heat the system's refrigerant.
- A failed pressure gauge — A bad gauge is possible but is not the usual explanation.
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