Question 2 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is D. **Why option D is correct:** The goal of purging is to remove non-condensable gases (primarily air) from the high side of the refrigeration system, typically near the condenser or receiver where they accumulate. Since air is heavier than refrigerant vapor when both are at typical system temperatures and pressures (or at least, the air separates to the top), the process inevitably involves releasing some refrigerant vapor along with the unwanted gases. To minimize the release of valuable refrigerant, the purging process must be done slowly and intermittently. "Cracking the purge valve briefly" means opening it just enough and for a short duration to allow the accumulated pocket of non-condensables to escape quickly before significant amounts of refrigerant vapor follow. "Allowing the refrigerant to re-settle between purges" ensures that the non-condensable gases have time to re-accumulate and stratify at the highest point, maximizing the concentration of non-condensables near the purge point for the next brief release. This slow, intermittent method is the standard best practice for minimizing refrigerant loss during manual purging. **Why the other options are incorrect:** * **A) purging through the top of the receiver rather than the top of the condenser:** While the receiver might be used for purging, the non-condensables generally concentrate at the highest point of the system when it is running (which is often the top of the condenser or a dedicated purge point connected there). Purging from the highest point where the gases accumulate (which could be the condenser or receiver, depending on system design) is necessary, but simply choosing the receiver over the condenser doesn't inherently minimize refrigerant loss; the *method* of purging (slowly and intermittently) does. Furthermore, the condenser is generally the intended high-side accumulation point for these gases. * **B) purging through the discharge service valve rather than the top of the condenser:** The discharge service valve is located near the compressor outlet and handles very hot, high-pressure, turbulent refrigerant vapor. Non-condensable gases are highly unlikely to accumulate efficiently at this location. Purging from here would result in releasing large amounts of refrigerant vapor without effectively removing the air, thereby maximizing refrigerant loss. The purge should always happen where the non-condensables settle (the condenser or receiver top). * **C) purging through a dehydrator:** A dehydrator (filter drier) is designed to remove moisture and contaminants (sludge, acid) from the *liquid* line of the system. It is not designed for, nor should it be used for, purging air and non-condensable gases from the high-pressure *vapor* side of the system. Attempting to use a dehydrator for this purpose is fundamentally incorrect and inefficient.