EPA Section 608 Universal Certification ExamType II (High-Pressure Appliances)Medium
A technician is using a self-contained (active) recovery unit to recover R-404A from a high-pressure commercial refrigeration system. The system's compressor has failed, but the system still contains a significant amount of liquid refrigerant. Which recovery method would be MOST efficient in this scenario?
- AVapor recovery only
- BLiquid recovery only
- CPush-pull liquid recovery
- DRecovering directly into a vacuum
Show answer & explanationAnswer & explanation
Correct answer: C. Push-pull liquid recovery
Push-pull recovery is the most efficient method for removing large amounts of liquid refrigerant from systems with an inoperative compressor. It uses the recovery machine to draw vapor from the recovery cylinder, creating a pressure differential that 'pulls' liquid from the system into the cylinder, and 'pushes' vapor from the cylinder back into the system to maintain the flow.
Why the other options are wrong
- A. Vapor recovery is very slow, especially with large amounts of liquid, as it relies on boiling off the liquid.
- B. Liquid recovery only, without the 'push' component, would be less efficient and could lead to cavitation in the recovery pump.
- D. Recovering directly into a vacuum is not a standard or efficient method for large liquid charges; a vacuum alone cannot move liquid quickly.
Push-Pull Liquid Refrigerant Recovery
A highly efficient method for recovering large quantities of liquid refrigerant from systems, especially when the system's compressor is inoperative, by creating a pressure differential that moves liquid.
- Uses the recovery machine to create a vapor pressure differential.
- Pulls liquid from the system to the recovery cylinder.
- Pushes vapor from the cylinder back into the system to aid flow.
- Most efficient for large liquid charges and non-operating compressors.
Memory trick: Push and Pull, makes recovery full!