Why might a technician add a trace amount of R-22 to the nitrogen used to pressure test a system?
So an electronic leak detector can sense the gas where it escapes. Detectors respond to halogenated refrigerants, not to nitrogen, and a small trace keeps refrigerant use low.
- So an electronic leak detector can sense the escaping gasCorrect answer
- To lubricate the compressor during the test
- To raise the test pressure without using any more nitrogen
- To dry out moisture inside the system
Why “So an electronic leak detector can sense the escaping gas” is correct
Electronic leak detectors respond to halogenated refrigerants, not to nitrogen. A small trace of R-22 in the nitrogen lets the detector find where the test gas escapes while keeping refrigerant use low.
Source: EPA: Test Topics
Why the other answers are wrong
- To lubricate the compressor during the test — A trace of refrigerant does not lubricate the compressor.
- To raise the test pressure without using any more nitrogen — The amount is too small to matter for pressure; nitrogen supplies the pressure.
- To dry out moisture inside the system — R-22 does not dry the system; evacuation removes moisture.
The source, word for word
Order of preference for leak test gases [nitrogen alone best, but nitrogen with trace quantity of
This one rests partly on trade knowledge. EPA's outline gives the order of preference, with nitrogen alone first and nitrogen plus a trace of R-22 ahead of pure refrigerant, but it doesn't say why the trace is used. The point about detectors is trade knowledge.
The order of preference
This is the order on EPA's outline for high-pressure systems.
- Nitrogen alone is the best choice.
- Nitrogen with a trace of R-22 comes next.
- Pure refrigerant is the last choice, because the refrigerant is released when the test gas is let out.
Related leak test points
Leak test before charging or recharging equipment, as EPA's outline also says. Never use oxygen or compressed air. The rule's own definition of a leak inspection also allows ultrasonic tests, gas-imaging cameras and bubble tests (40 CFR 82.152).
Keep practicing
- Which gas to use for leak testing
- How often leak inspections are required at 500 pounds or more
- EPA leak repair rules
- EPA 608 Type 2 practice test
- EPA 608 Type 2 mock exam
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.