9.4 Type III Leak Testing and Water-Side Issues

9.4 Type III Leak Testing and Water-Side Issues

Leak testing on low-pressure systems requires different techniques than high-pressure systems because the systems operate in vacuum. Additionally, water-side issues can significantly affect both system performance and refrigerant integrity.

Leak Testing Low-Pressure Systems

Since low-pressure systems operate below atmospheric pressure, conventional pressurization for leak testing requires special considerations:

Pressurization for leak testing:

• Use dry nitrogen to pressurize the system for leak testing
• Never exceed the system's rated working pressure — typically much lower than high-pressure systems
• A common test pressure is 10-15 psig for low-pressure chillers
• Never use refrigerant alone to pressurize for leak testing (wasteful and potentially illegal)
• Add a trace of refrigerant to the nitrogen to enable electronic detection

Standing vacuum test:

1. Evacuate the system to a deep vacuum
2. Isolate the vacuum pump
3. Monitor for pressure rise over 24 hours
4. Any significant rise indicates a leak (or moisture evaporating from within the system)
5. If pressure rises due to moisture rather than air, the system needs additional evacuation

Finding Leaks in Low-Pressure Systems

Water-Side Contamination: The Tube Failure Problem

One of the most serious problems in low-pressure chillers is tube failure — when a tube in the evaporator or condenser develops a crack or hole:

What happens:

1. Since the evaporator operates in vacuum, water is pulled through the tube failure INTO the refrigerant
2. Water contamination causes:
   • Acid formation (water + refrigerant at high temp = hydrochloric/hydrofluoric acid)
   • Copper plating (acid dissolves copper, which deposits on bearing surfaces)
   • Sludge formation (degraded oil and refrigerant byproducts)
   • Compressor bearing failure (copper plating and acid damage)

Detection:

• Acid test of the oil — reveals pH changes indicating water contamination
• Moisture test of the refrigerant — detects water in the system
• Sight glass color — yellow indicates moisture/acid
• Purge unit behavior — water entering creates additional NCG activity

Eddy Current Testing

Eddy current testing is a non-destructive testing method used to inspect chiller tubes for defects:

• An electromagnetic probe is inserted into each tube
• The probe detects variations in tube wall thickness (thinning, pitting, cracking)
• Identifies tubes that are failing or likely to fail soon
• Should be performed during routine maintenance or when water contamination is suspected
• Defective tubes are typically plugged to prevent future leaks

Oil and Acid Management

Low-pressure systems require careful attention to oil condition:

• Oil analysis: Regular sampling and testing for acid level, moisture, and debris
• Acid removal: If acid is detected, the oil must be changed and the system may need extended operation with acid-neutralizing additives
• Oil heating during shutdown: The oil sump heater must remain energized during shutdown to prevent refrigerant migration into the oil (which would dilute the oil and cause bearing damage on startup)

For the Exam: Water enters low-pressure evaporators through tube failures (vacuum pulls water in). This causes acid, copper plating, and sludge. Eddy current testing inspects tubes for defects. Oil sump heaters must stay ON during shutdown to prevent refrigerant migration.