1. Unit 8: Leak Detection, System Evacuation, and System Clean-up
Section 2: Safety, Tools and Equipment, and Shop Practices
Unit 8: Leak Detection, System Evacuation, and System Clean-up

2. Objectives After studying this unit, you should be able to:
Describe a standing pressure test
Describe the six classes of leaks
Explain the test procedures for evaporator and condenser leaks
Explain the test procedures for suction and liquid leaks

3. Objectives (cont’d.)
Explain the test procedures for temperature, pressure and vibration dependent leaks
Choose a leak detector for a particular type of leak
Describe a deep vacuum
Describe two different types of evacuation
Describe two different types of vacuum measuring instruments

4. Objectives (cont’d.) Choose a proper high-vacuum pump
List some of the proper evacuation practices
Describe a deep-vacuum single evacuation
Describe a triple evacuation
Explain the process involved with cleaning a system after a hermetic motor burn-up

5. Leaks and Leak Checking
All sealed systems leak
“Flaws" exist at every joint fitting, seam, or weld
May be too small to detect but given time, vibration, temperature, and environmental stress, these flaws become larger detectable leaks

6. Exposing the Leak Sight
Vapor can flow under layers of paint, flux, rust, slag, and pipe insulation
Important to clean the leak site by removing loose paint, slag, flux, rust, or insulation

7. Six Classes of Leaks Standing leaks Pressure dependent leaks
Detected while the unit is at rest or off
The most common of all leaks
Pressure dependent leaks
Detected as the system pressure increases
Temperature dependent leaks
Associated with the heat of expansion

8. Six Classes of Leaks (cont’d.)
Vibration dependent leaks
Occur during unit operation
Combination dependent leaks
Require two or more conditions to leak
Cumulative micro-leaks
All the individual leaks that are too small to detect with standard tools

9. Basic Leak Detection
Spotting refrigerant oil residue for standing leaks
Testing for evaporator section leaks
Testing for condensing section leaks
Suction and liquid line leak test

10. Advanced Leak Detection
Testing for pressure dependent leaks
Testing for temperature dependent leaks
Testing for vibration dependent leaks
Testing for combination dependent leaks

11. Standing Pressure Test
Visually inspect the newly assembled system
Solder joints should have no gaps
Flanged and threaded connections should be tight
Control valves should be installed properly
All service valve covers should be in place

12. Standing Pressure Test (cont’d.)
Figure 8–12 Isolating the compressor to pressurize the condenser and evaporator

13. Standing Pressure Test (cont’d.)
Performing a standing pressure test:
Pressurize the system with dry nitrogen to a pressure no higher than the lowest system test pressure
Allow the system to rest for five minutes
Mark the needle positions on the gauge manifold
Monitor gauge needle position

14. Leak Detecting Methods
Audible leaks are large and relatively easy to locate
Halide leak detector
Ultrasonic leak detector
Ultraviolet leak detectors
Electronic leak detectors

15. Leak Detecting Methods (cont’d.)
Figure 8–13 Listen for leaks

16. Leak Detecting Methods (cont’d.)
Figure 8-14 When using a pressure gauge for a standing leak test, tap it lightly to make sure the needle is free, then mark the gauge

17. Leak Detecting Tips
The system must be evacuated to required vacuum levels
Visual inspection for oil and dirt spots
Leaks can be caused by vibration or temperature
Leak check gauge ports prior to gauge installation

18. Repairing Leaks Per EPA, these do not require repair:
Systems with less than 50 lbs of refrigerant
Some industrial/commercial systems with more than 50 lbs of refrigerant and a leak rate less than 35% per year
Comfort cooling chillers with a leak rate of less than 15% per year
Most residential systems

19. Purpose of System Evacuation
Air contains oxygen, nitrogen, hydrogen, water vapor
Nitrogen is a non-condensable gas
Non-condensables will cause a rise in the system’s operating head pressure
Oxygen, hydrogen, and water vapor cause chemical reactions in the system
Produces acids that deteriorate system components and can cause copper plating

20. Purpose of System Evacuation (cont’d.)
Chemical combinations create hydrofluoric or hydrochloric acids
Evacuation = degassing + dehydration
Moisture + acid + oil = sludge
Sludge can cause system components to become plugged
Proper evacuation can eliminate the formation of acid and sludge

21. Theory Involved with Evacuation
Pulling a vacuum lowers the pressure in a system below atmospheric
Atmospheric pressure = psia
Psia = atmospheric pressure + gauge pressure (psig)
Degassing the system removes non-condensable gases
Systems should be evacuated from the high and low pressure sides of the system

22. Measuring the Vacuum Tips
1 micron = 1/1,000 of a millimeter ; 1,000 microns = 1 mm; 1 micron = 1/25,400 in.
Best methods to measure
Electronic (thermistor) vacuum gage
Analog, digital, or light-emitting diode (LED)
U-tube manometer
Should reach at least 250 microns if there are no leaks in the system

23. Measuring the Vacuum (cont’d.)
Figure 8-24 (A) A modern, hand-held, digital electronic micron gauge (B) Modern electronic vacuum gauges for measuring a deep vacuum Courtesy Ferris State University Photo by John Tomczyk

24. Recovering Refrigerant
If there is or has been refrigerant in that system, the technician must remove the refrigerant
Must be done with EPA-approved recovery equipment

25. The Vacuum Pump Two-stage vacuum pumps produce the lowest vacuum
EPA mandates systems reach at least 500 microns during evacuation
Very low vacuums cause moisture inside a sealed system to boil to a vapor, which is then removed by the pump and released to the atmosphere

26. Deep Vacuums Measured in the 250- to 500-micron range
Once proper micron levels are reached, the vacuum pump is valved off
When system pressure is reduced to the required vacuum level and remains constant, no noncondensable gas or moisture is left in the system

27. Multiple Evacuation Accomplished by:
Evacuating a system to a low vacuum, about 1,500 microns
Allowing a small amount of dry nitrogen to bleed into the system
The nitrogen then blown to the atmosphere
System is then evacuated until the vacuum is again reduced to 1,500 microns

28. Leak Detection While in a Vacuum
Checking for a leak by watching to see if the pressure rises on a vacuum gauge is not recommended
If there is a leak during the problem, air is allowed to enter the system
This method only proves that the system will not leak under a pressure difference of (atmospheric pressure)

29. Removing Moisture with a Vacuum
Figure 8–42 When a system has moisture in it and is being evacuated, heat may be applied to the system. This will cause the water to turn to vapor, and the vacuum pump will remove it

30. General Evacuation Procedures
Cold trap
Do not start a hermetic compressor while it is in a deep vacuum
Apply heat to the compressor to assist in removing water trapped under the oil
Gauge manifolds with large valve ports and hoses help speed evacuation
Schrader stem depressors can be removed

31. Systems with Schrader Valves
Take longer to evacuate than systems with service valves
Field service valves are used to replace Schrader valve stems while the system is under pressure
Schrader valve caps should be put back on the valve after service

32. Gauge Manifold Hoses and System Valves
Hoses can have pinhole leaks and slow down the evacuation process
Using copper tubing for the gage lines will help eliminate evacuation problems
Check system valves to verify they are open before evacuation
Closed valves can trap air in the system

33. Using Dry Nitrogen Tips Sweeping dry nitrogen through a sealed system
Helps keep the atmosphere out of the system
Helps clean the piping of the system
Do not pressurize with pressures above the system’s test pressures
Never start a system that is pressurized with nitrogen

34. Cleaning a Dirty System
Formation of acid, soot, and sludge
Created by heat that causes refrigerant and oil to break down
Cannot be removed from a system with a vacuum pump
Fumes can be toxic
Safety goggles and gloves should be worn

35. Summary
Common leak detection methods: include the halide torch, ultrasonic leak detector, electronic leak detector, and the ultraviolet leak detector
System evacuation removes moisture from the system prior to putting the system into operation

36. Summary (cont’d.)
Evacuation reduces the formation of acid and sludge, and removes system noncondensables
Vacuums can be measured with micron gauges
Evacuation = Dehydrating + Degassing

37. Summary (cont’d.) Systems should not be leak checked in a vacuum
Removing Schrader valves and pin depressors will help to speed the evacuation process