Tech Tip: Servicing A/C systems with high-voltage compressors

If your shop services air conditioning systems you’ve most likely heard special oil and equipment is needed when servicing systems that utilize high-voltage (HV) compressors.  These systems have been in use for around 10 years now.  Even though these aren’t new by any means, there are still myths related to the reason for the special oil and service equipment.  Hopefully this will help shed some light on the reason for the issue.

Systems that utilize HV compressors do not allow the use of PAG oil because it can result in an isolation fault (high-voltage leak to the chassis).  PAG oil, however, is not actually the cause of the insulation failure.  PAG oil is hygroscopic, which simply means that it readily absorbs moisture.  As the moisture content of the PAG increases the conductivity (the ability to conduct electricity) also increases.  If the HV compressor has developed a problem with the insulation of the motor windings (cracks, etc.) this moisture-contaminated PAG oil can provide a path for the high-voltage to leak to the vehicle chassis.  In other words, the PAG oil isn’t the cause of the problem but rather allows a problem that already exists to become evident.     

By utilizing the correct oil in the system (generally P.O.E.) and an A/C service machine capable of preventing cross-contamination between the PAG and P.O.E. oils you should avoid any problems.  Keep in mind that leak detection dye is carried by A/C oil as well, so make sure the dye you use in these systems is compatible with P.O.E. oil and doesn’t contain PAG oil.   

If there is any doubt about the proper oil for an A/C system utilize a reference such as the online “Mobile A/C Specifications Library” available from the Mobile Air Conditioning Society.

Information provided by: AR&D