CSLB C-20 HVAC ContractorCooling and RefrigerationEasy
A technician wants to pressure test a repaired refrigeration system for leaks using a compressed gas. Which gas is strictly prohibited for this purpose because it can react explosively with refrigerant oil residue under pressure?
- ADry nitrogen
- BCarbon dioxide
- CNitrogen with a trace of refrigerant
- DOxygen
Show answer & explanationAnswer & explanation
Correct answer: D. Oxygen
Oxygen must never be used to pressure test refrigeration systems because it can combine explosively with refrigerant oil under pressure, posing a serious fire and explosion hazard. Dry nitrogen (often mixed with trace refrigerant for leak detection) is the industry-standard safe alternative.
Why the other options are wrong
- A. Dry nitrogen is the standard safe gas used for pressure testing.
- B. CO2 is not typically used but is not the prohibited explosive-risk gas referenced here.
- C. Nitrogen with trace refrigerant is a common accepted leak-detection method.
Prohibited Test Gas — Oxygen
Oxygen is never used for pressure testing refrigeration systems due to explosion risk when combined with compressor oil under pressure.
- Only dry nitrogen (sometimes with trace refrigerant) is approved for pressure testing
- Oxygen + oil under pressure = explosion hazard
- OSHA and industry standards prohibit oxygen use in this application
Memory trick: Oxygen feeds fire — never let it near your refrigeration wire.