What usually causes the pressure to rise in an R-22 system that has just been pulled down to its recovery vacuum?
Refrigerant is still in the system. Liquid left in low spots, or refrigerant dissolved in the compressor oil, keeps boiling off after the machine stops, and that vapor raises the pressure.
- 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.
The source, word for word
Need to wait a few minutes after reaching required recovery vacuum to see if system pressure rises (indicating that there is still liquid refrigerant in the system or in the oil)
technicians must evacuate the refrigerant, including all the liquid refrigerant, to the levels in Table 1
What to do when it happens
Reaching the number once is not enough, because the rule requires all the liquid refrigerant to be out. Wait a few minutes with the machine valved off and watch the gauge. If the pressure climbs, restart recovery and repeat until it holds at the required level.
EPA's outline gives no boiling pressure for the oil itself. It is the refrigerant in the oil that boils off, at a pressure set by the refrigerant and its temperature, so a pressure-temperature chart is the tool for reading it.
Keep practicing
- Pressure-temperature chart basics
- EPA refrigerant recovery rules
- The evacuation level for disposing of a low-pressure chiller
- EPA 608 Type 2 practice test
- EPA 608 Type 2 mock exam
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.