Servicing Electric A/C Compressors: Safety and Best Practice

Electric air-conditioning compressors have been around for a while, and most technicians have seen one or at least heard of them. Bear in mind that EVs are expected to account for 20 percent of new vehicle sales by 2030, which means more and more electric A/C vehicles will be coming into your bay.

The basic principle of air conditioning has not changed: refrigerant still absorbs cabin heat through the evaporator, and the condenser turns it back into usable liquid. What has changed is the service procedure.

Safety first. These compressors operate at up to 400 volts. High-voltage circuits can be identified by the orange cable connected to them. If the compressor has to be replaced, follow the manufacturer's high-voltage shutdown procedure exactly. These procedures typically require Class 0, 1000-volt high-voltage gloves with leather over-gloves to protect them from damage, plus a CAT III multimeter to confirm that the high-voltage components being worked on are de-energised.

Pay particular attention to the type of oil an electric compressor uses, which is generally different from mechanically driven compressors and is covered in numerous technical service bulletins. High-voltage compressors require a non-conductive polyol ester (POE) air-conditioning oil, with the specific grade specified by the vehicle manufacturer.

Never use any compressor oil other than the one the manufacturer recommends. This oil has high dielectric properties that help preserve the integrity of the insulation on the compressor motor windings, preventing high-voltage current from reaching the compressor housing and protecting the technician from shock.

Equally important: never allow PAG oil into these systems. Even one percent PAG oil in the system can drop the compressor's insulation resistance from over 10 megohms to below 1 megohm, triggering a fault code and potentially shutting the compressor down. Many vehicle manufacturers require the entire air-conditioning system to be replaced after cross-contamination with PAG oil.

Finally, watch the leak-detection dye added to the system. Just as the wrong oil contaminates the system, the wrong dye will too. Remember that electric compressors take a specific dye: EV leak-detection dye is polyol ester based and varies by model. A simple way to avoid cross-contamination is to keep dedicated hoses and charging tools for each type of refrigerant oil. Equipment previously used on conventional A/C systems can contaminate a high-voltage system, and that is worth taking seriously.