EPA Section 608 Universal Certification ExamType III (Low-Pressure Appliances)Medium
When charging a low-pressure chiller with R-123, which of the following is the safest and most effective method to ensure that liquid refrigerant does not enter the compressor?
- ACharge into the condenser with the system off.
- BCharge through the liquid line service valve as a liquid.
- CCharge through the low-side service valve as a vapor.
- DCharge into the evaporator with the system operating.
Show answer & explanationAnswer & explanation
Correct answer: C. Charge through the low-side service valve as a vapor.
Charging as a vapor through the low-side service valve (suction line) is the safest method to prevent liquid refrigerant from entering the compressor, as the refrigerant will vaporize before reaching the compressor intake. While charging liquid into the evaporator is possible with the system operating, charging vapor is inherently safer for the compressor.
Why the other options are wrong
- A. Charging into the condenser with the system off would not effectively distribute the charge and could lead to an incorrect charge amount or system damage upon startup.
- B. Charging liquid directly into a running compressor via the liquid line is highly dangerous and can cause slugging.
- D. Charging liquid into the evaporator *can* be done carefully with the system operating, but vapor charging is generally safer for compressor protection and less prone to slugging. The question asks for the *safest* and *most effective* to prevent liquid from entering the compressor.
Low-Pressure Chiller Charging Method (Safety)
For safe and effective charging of a low-pressure chiller, especially to protect the compressor, it's crucial to introduce refrigerant in a controlled manner, typically as a vapor.
- Vapor charging prevents slugging.
- Charge through low-side (suction).
- Liquid charging requires extreme care or specific ports.
Memory trick: Vapor to the low side, keeps the compressor pride!