Which statement is true about leak testing?

• A. A drop in temperature always indicates a leak.
• B. The testing uses the lowest pressure.
• C. The leak site should be cleaned before brazing or soldering.
• D. After leak testing, refrigerant is charged immediately.

Answer: (C)

Cleaning the leak site before brazing or soldering is essential because proper joint quality depends on clean, oxide-free metal surfaces. When you braze or solder, filler metal must wet the surfaces and flow evenly into the joint. Oils, dirt, or oxide films at the leak site hinder wetting and bonding, creating voids or weak spots that can cause leaks later. Removing these contaminants ensures the filler metal can form a strong, airtight seal.

Temperature changes aren’t a reliable sign of a leak, since a drop in temperature can occur for other reasons and isn’t definitive. Leak testing also isn’t done at the lowest pressure; the test pressure is chosen to reveal leaks without risking damage to the components. And after leak testing, refrigerant isn’t charged immediately; the system is typically evacuated to remove air and moisture and then charged once the integrity of the joints is confirmed.