Free HVAC TrainingRefrigeration leaks a quite common in air conditioning and heat pump systems and can be difficult to detect. It takes practice, practice, and the right tools. There are different types of leaks as classified by Refrigeration Technologies, the makers of BigBlu Micro Leak Detector Solution. At some time during your servicing experience, you will run across them all.

  • Class 1. Standing Leaks (SL) are leaks that can be detected while the unit is at rest (off) and fully equalized. This shall include freezer evaporative coils warmed up by defrost. SL leaks, fortunately, are the most common of all.
  • Class 2. Pressure Dependent Leaks (PDL) are leaks that can only be detected as the pressure is built. Nitrogen is used to pressurize low sides to 150 psi and high sides to 450 psi. Never use CO2 or Oxygen. Helium or dry air is acceptable. PDL testing should be conducted if no leaks are discovered by the SL test.
  • Class 3. Temperature Dependent Leaks (TDL) are leaks associated with the heat of expansion. TDL usually occurs from high ambient air, condenser blockage or during defrost.
  • Class 4. Vibration Dependent Leaks (VDL) occur only during unit operation. The mechanical strain of motion, rotation, refrigerant flow, or valve actuation are all associated with VDL.
  • Class 5. Combination Dependent Leaks (CDL) are flaws that require two or more conditions in order to induce leakage. For example, temperature, vibration and  pressure cause the discharge manifold on a semi-hermetic compressor to expand and seep gas.
  • Class 6. Cumulative Micro-Leaks (CML) are all the individual leaks that are too small to detect with standard tools. The total loss over many years of operation slightly reduces the initial gas charge. In practice, a system having many fittings, welds, seams or gasket flanges; the greater the amount of CML.

It is important to understand the different types of leaks in order to properly test for them.

In most residential HVAC systems the leaks occur in the evaporator coil, condensing coil, suction line dryer, or accumulator. These types of leaks are not usually repairable and require replacement of  the leaking component. These are normally SL leaks.  VDL leaks are often found after many years of use when refrigerant piping within the unit has been rubbing on something causing a hole in the piping.

Our HVAC Certification Course covers leak detection, HVAC repair, refrigeration theory, and more.

by Ron Walker

Ron Walker
Ron Walker

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.