Today's units sometimes don't have a magnetic clutch assembly.
Surprise! On some of the compressors in use today, there is no magnetic clutch assembly on the compressor for you to see. Here's a short rundown of the different compressors that may make their way to your shop.
Constant Run Variable Displacement CompressorsIt takes a lot of energy to spin a compressor. On some vehicles, it can take more energy to run the compressor than it does to run the car at a steady cruise, and that affects fuel mileage and emissions. One answer to reducing that effect is the variable displacement compressor. After all, less refrigerant volume is needed to keep a car cool than is needed to get it cool, and less energy is needed to pump that reduced volume.
The displacement also can be externally controlled, typically by the Engine Control Module (ECM) in response to information it gets from refrigerant pressure and temperature sensors. This provides for more precise control over the displacement needed for optimum cooling while reducing the power demand on the engine.
Be aware that your gauge pressures may read just fine. Pressure readings are not dependent on volume. One indicator of a problem related to displacement is a system that is cooling, but not as well as it should. Gauge readings may be near normal or the low side readings may be slightly higher than normal. Both are symptoms of insufficient refrigerant volume through the evaporator, similar to what you might see with a clogged orifice tube.Include temperature readings at the ducts in your diagnostic process. If you suspect a problem, you will need a scan tool to test externally controlled compressors and, on some, a special tool to substitute the ECM's control to vary the displacement yourself. On most, any failure associated with the compressor requires replacement of the assembly.
Electric CompressorsHybrids are becoming more and more common, and most rely — either directly or indirectly — on the A/C system to keep the high voltage (HV) battery packs cool. Considering the age of the hybrid fleet, this is an A/C market you should become a part of. While some hybrids use conventional fixed displacement, belt driven compressors, many are using electric compressors.
Because both of these designs use high voltage electric motors internal to the compressor, they require special, non-conductive (designated POE) oil for lubrication. Even a slight contamination (less than 1 percent) with PAG oil can result in voltage leaking through the compressor case. To service these systems, you'll need a dedicated RRR (recovery/recycling/recharging) machine just for hybrids or a new machine that is certified to SAE standard J2788H.
This applies even if all you do is recover the charge to fix a leaking seal. There is enough oil remaining in your current machine's lines to cause sufficient contamination. Failing to follow this guideline can result in a comeback where at least one manufacturer requires EVERY component in the system be replaced.
On the Horizon?
No doubt about it, new refrigerants are on the horizon. Mandated by the European Union, R-134a will no longer be allowed in new platforms offered for sale there in the 2011 model year. Leading contenders for the replacement of R-134a are CO
Pete Meier is an ASE CMAT, member of iATN, and full-time tech in Tampa, Fla. His experience reaches back more than 30 years, and his contributions to Motor Age reflect a wide variety of experience with almost every make and model. You can contact Meier at www.autoservicetech.com.