ASE G1 Auto Maintenance and Light RepairHeating and Air Conditioning (HVAC)Medium
A technician is preparing to recover refrigerant from an R-134a automotive AC system. According to EPA regulations, what is the MINIMUM vacuum level (in inches of mercury, Hg) that must be achieved before recharging a system that has been opened for service?
- A15 inches Hg
- B29.92 inches Hg (full vacuum)
- C10 inches Hg
- D20 inches Hg
Show answer & explanationAnswer & explanation
Correct answer: B. 29.92 inches Hg (full vacuum)
EPA regulations (specifically section 609 for MVAC) mandate that a system opened for service must be evacuated to at least 29.92 inches Hg (a full vacuum) to remove all non-condensable gases and moisture before recharging.
Why the other options are wrong
- A. 15 inches Hg is insufficient for proper moisture and non-condensable gas removal.
- C. 10 inches Hg is insufficient for proper moisture and non-condensable gas removal.
- D. 20 inches Hg is insufficient for proper moisture and non-condensable gas removal.
MVAC Evacuation Standard
For MVAC systems opened for service, EPA Section 609 requires evacuation to a full vacuum (29.92 inches Hg) to remove all air and moisture.
- Removes non-condensable gases (air).
- Boils off moisture at lower temperatures.
- Prevents acid formation and system damage.
- Crucial for system efficiency and longevity.
Memory trick: Full vacuum is the rule, for a system that's cool.