EPA Section 608 Universal Certification ExamType III (Low-Pressure Appliances)Hard
After recovering refrigerant from a low-pressure appliance, a technician finds that the system pressure has risen from the required vacuum to 0 psig within a few minutes. What is the most likely cause?
- AThe system still contains liquid refrigerant that is boiling off.
- BThe system contains non-condensable gases.
- CThe recovery unit's pump is malfunctioning.
- DThe recovery cylinder is full.
Show answer & explanationAnswer & explanation
Correct answer: A. The system still contains liquid refrigerant that is boiling off.
If a low-pressure system's pressure rises quickly from a deep vacuum to 0 psig, it indicates that there is still liquid refrigerant present that is boiling off and creating vapor pressure. Non-condensables would cause a pressure rise, but typically not from a deep vacuum to 0 psig so rapidly, and they are usually removed to a degree by the recovery process itself.
Why the other options are wrong
- B. While non-condensables can cause a pressure rise, a rapid rise from a deep vacuum to 0 psig is more indicative of remaining liquid refrigerant boiling, as non-condensables would likely have been partially removed during recovery and wouldn't create such a quick, significant pressure increase.
- C. A malfunctioning pump would prevent reaching the vacuum, but wouldn't cause a rise in pressure after the pump is isolated and vacuum achieved.
- D. A full recovery cylinder would prevent further recovery, but wouldn't cause the system's internal pressure to rise from a vacuum.
Post-Recovery Pressure Rise (Low-Pressure)
A rapid increase in system pressure from a required vacuum level after refrigerant recovery, indicating the presence of residual liquid refrigerant boiling off.
- Occurs after recovery to a deep vacuum.
- Pressure rises quickly (e.g., to 0 psig).
- Primary cause: remaining liquid refrigerant.
- Requires further recovery or heat application.
Memory trick: Vacuum held, then pressure grows, liquid's boiling, everyone knows!