EPA Section 608 Universal Certification ExamType III (Low-Pressure Appliances)Hard
A technician is preparing to charge a low-pressure chiller with R-123. Which of the following is the safest and most accurate method for adding the initial charge to the system?
- AIntroducing liquid refrigerant into the evaporator through the rupture disc port.
- BIntroducing liquid refrigerant into the low-side charging valve with the compressor running.
- CIntroducing liquid refrigerant into the high-side charging valve.
- DIntroducing vapor refrigerant through a charging valve on the lowest possible point of the system.
Show answer & explanationAnswer & explanation
Correct answer: D. Introducing vapor refrigerant through a charging valve on the lowest possible point of the system.
Introducing vapor refrigerant first, through the lowest possible point, is safest to avoid freezing chiller tubes and to ensure the system pressure rises above 0 psig before any liquid is introduced. While subsequent liquid charging is done by weight, the initial vapor charge is critical for safety.
Why the other options are wrong
- A. The rupture disc port is for emergency pressure relief, not for charging refrigerant. Introducing liquid directly into the evaporator without proper pressure control is very risky.
- B. Introducing liquid into the low side with the compressor running is extremely dangerous and can cause compressor damage (slugging).
- C. Introducing liquid into the high side is generally avoided for initial charging, especially in a vacuum, due to potential for freezing and slugging if pressure is not controlled.
Low-Pressure Chiller Initial Charging Method
The safest initial charging method for a low-pressure chiller is to introduce vapor refrigerant through a charging valve at the lowest possible point of the system until pressure rises above 0 psig.
- Start with vapor.
- Charge into the lowest point (often evaporator).
- Raise pressure above 0 psig.
- Prevents freezing of water in tubes.
- Subsequent liquid charge is by weight.
Memory trick: Start 'Low and Slow' with vapor, then 'Rise Up' to safety.