Question 14 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is A. **Explanation for Option A (Correct):** Option A is correct because charging liquid refrigerant into the low-pressure side (suction line) while the compressor is running creates a serious risk of hydrostatic lock or slugging. Liquid refrigerant is incompressible. If liquid enters the compressor cylinder, it can cause severe damage to the valves, pistons, and rods due to the enormous pressure generated when the piston attempts to compress the liquid. Therefore, when charging refrigerant as a liquid into an operating vapor compression system, it must be introduced into the high-pressure side (e.g., the liquid line, condenser outlet, or receiver) where it immediately mixes with the existing liquid charge or condenses without posing a threat to the running compressor. **Explanation of Incorrect Options:** **B) when charging as a liquid it should be to the low side only:** This is incorrect. As explained above, charging liquid directly into the low side (suction line) while the compressor is operating is highly dangerous and risks severe compressor damage (slugging/hydrostatic lock). **C) when charging as a vapor it should be directly to the receiver only:** This is incorrect. Charging as a vapor is typically done through the low side (suction line) to avoid pressure equalization issues and to allow the compressor to slowly draw the refrigerant in. While vapor can be charged into the high side (like the receiver) if the system is shut down or evacuated, the primary method for adding vapor to an operational system is the low side. Stating it should *only* be to the receiver is restrictive and inaccurate. **D) when charging as a liquid it may be to the low or high side:** This is incorrect. While liquid can technically be charged to the low side *if the system is shut down and evacuated* (a procedure often done through the liquid line or receiver connection, then filling), the general rule for an *operating* system is that liquid must only go to the high side. Stating it *may* go to the low side implies safety under normal operation, which is false and dangerous.