Major Air Systems Ltd. offers a number of different types of non-destructive testing and has extensive experience interpreting the results of these tests.
• Dielectric Strength Testing
• Vibration Analysis
• Eddy Current Tube Analysis
• Wear Metals Oil Analysis
• Refrigerant Analysis
• Infrared Thermal Imaging
A sample of oil is analyzed for metal, moisture and acid content. Over a period of time a trend is established. To be most useful the analysis has to be continuous from the last overhaul or from first commissioning so that, wear metals and acid numbers can tell the internal condition of the machine without opening the machine. However, the analysis can tell the quality of service over several years as the wear, moisture and acid numbers reduce to normal areas for long and reliable operation. Major Air uses a laboratory in La Crosse Wisconsin that has analyzed air conditioning equipment oil samples for over forty years.
Dielectric motor winding testing
A highly accurate megger is used to impress a known voltage on each winding of a star delta, motor and the leakage current to ground is measured over a timed period. The same type of test is undertaken between windings. An air conditioning type motor has a distinct signature. A trend line will show gradual deterioration of the insulation so that the motor can be repaired during a scheduled shut down rather than being surprised during the peak of the cooling season.
Eddy current tube analysis
A probe that has opposing magnetic fields is passed down the tube. The magnetic fields measure the inside of the tube against the outside of the tube. Depending on how the magnetic probe is wound and the experience of the operator various tube defects can be detected. Pits on the inside or outside of the tube, erosion of the tube at the support, zipper cracks, circumferential cracks, and freezing type bulges, are some of the defects that can be determined. Usually an equipment insurance company will require an eddy current tube analysis every three to five years.
A specialized piece of electronic equipment is used to take vibration signatures at various points and in various planes on an air conditioning compressor. The signatures are then compared to a severity chart and over a period of time with each signature taken to determine excess vibration that could cause failure of the equipment. This type of non-destructive testing is more useful on equipment with gears and /or roller or ball bearings. On units with sleeve bearings, the wear has to be extremely excessive to show up.