8.3 Type II: Leak Detection and Repair

8.3 Type II: Leak Detection and Repair

Leak detection and repair are among the most critical skills for Type II technicians. High-pressure systems are the most common in the field, and proper leak management prevents environmental damage, reduces costs, and maintains system performance.

Leak Rate Triggers for Type II Systems

Leak Detection Best Practices for High-Pressure Systems

Step 1: Determine if a leak exists

• Review service history and refrigerant addition records
• Calculate annualized leak rate
• Perform a standing pressure test if needed

Step 2: Locate the leak

• Use an electronic leak detector (most effective for general area)
• Move probe slowly (1 inch/second) along all connections, fittings, and joints
• Check the lowest points first — refrigerant is heavier than air
• Use bubble solution to pinpoint exact leak location after the area is identified
• Common leak locations: Schrader valve cores, flare connections, brazed joints, service valve packing, condenser coils, evaporator coils

Step 3: Repair the leak

1. Recover the refrigerant to the required level
2. If brazing: evacuate and nitrogen-purge during brazing
3. Complete the repair
4. Pressure test with dry nitrogen
5. Evacuate the system (pull a deep vacuum)
6. Recharge with the correct refrigerant
7. Verify the repair with a follow-up leak test

Nitrogen Pressure Testing After Repair

After completing a leak repair:

1. Pressurize the system with dry nitrogen to the system's rated working pressure (or manufacturer's specification)
2. Never exceed the rated pressure
3. Always use a pressure regulator on the nitrogen tank
4. Allow the system to sit for a minimum of 10-15 minutes (longer for larger systems)
5. Monitor the pressure gauge for any drop
6. If pressure drops, the leak was not fully repaired — relocate and fix

System Evacuation After Repair

After a successful pressure test:

1. Release the nitrogen from the system
2. Connect a vacuum pump
3. Pull a deep vacuum to 500 microns (or manufacturer specification)
4. Hold the vacuum for a minimum of 10 minutes
5. If the vacuum rises above 1,000 microns, there is still moisture or a leak
6. A system that holds below 500 microns is properly evacuated and leak-free

Common High-Pressure System Problems

For the Exam: After repair: nitrogen pressure test → release nitrogen → deep vacuum to 500 microns → hold test → recharge. Non-condensable gases (NCGs) in a system cause high head pressure. The system should hold below 500 microns during a standing vacuum test.