EPA Section 608 Universal Certification ExamType III (Low-Pressure Appliances)Medium
A technician is preparing to charge a low-pressure refrigeration system with R-123. Which of the following is the correct procedure to ensure the system is properly dehydrated and ready for charging?
- AEvacuate the system to 15 inches of Hg vacuum, then break the vacuum with nitrogen.
- BEvacuate the system to 0 psig and immediately begin charging.
- CEvacuate the system to 25 mm Hg absolute or lower, then verify by holding the vacuum.
- DEvacuate the system to 29.9 inches of Hg vacuum and hold for 15 minutes to check for leaks.
Show answer & explanationAnswer & explanation
Correct answer: C. Evacuate the system to 25 mm Hg absolute or lower, then verify by holding the vacuum.
For low-pressure systems, proper dehydration requires evacuating to a deep vacuum of 25 mm Hg absolute or lower. Holding the vacuum after evacuation is crucial to ensure no leaks are present and that moisture has been removed.
Why the other options are wrong
- A. 15 inches of Hg vacuum is not a deep enough vacuum for proper dehydration and breaking with nitrogen is typically done to aid in leak checking or to raise pressure, not as part of the final evacuation for dehydration.
- B. 0 psig is atmospheric pressure and does not remove non-condensables or moisture.
- D. 29.9 inches of Hg vacuum is approximately 500 microns, which is an acceptable level, but '25 mm Hg absolute' (approx 984 microns) is a common standard specifically cited for low-pressure systems, and the option phrasing 'hold for 15 minutes to check for leaks' is less precise than verifying by holding the vacuum for stability.
Low-Pressure System Evacuation Standard
The required vacuum level and verification method for low-pressure refrigeration systems to ensure proper dehydration and readiness for charging.
- Target vacuum: 25 mm Hg absolute or lower.
- Purpose: Remove non-condensables and moisture.
- Verification: Hold vacuum to check for rise (indicating leaks or moisture).
Memory trick: Low pressure, deep vacuum, 25 is the key, then hold it to see.