Servicing HV Compressors

Jan. 1, 2020
In the early days of hybrid cars, a conventional belt-driven compressor provided cool air to the passenger compartment. The only problem with that? The gasoline engine (ICE) had to be running to turn on the compressor.

A SAE standard is in place, but questions over servicing electric compressors persist.

compressor. Hybrid repair shop training technician training A/C training automotive aftermarket In the early days of hybrid cars, a conventional belt-driven compressor provided cool air to the passenger compartment. The only problem with that? The gasoline engine (ICE) had to be running in order to turn the compressor and that limited, if not eliminated, the fuel savings hybrid owners saw in city driving. No idle stop mode. Toyota figured out a way around that by being the first to use an electric A/C compressor on the 2004 Prius. Now, almost half of all hybrids in the marketplace use electric compressors (some older Honda hybrids use a combination electric/belt driven compressor) and of course, all the EV offerings use them.

The primary issue you need to be critically aware of when servicing these systems centers around one word: oil.

What's So Special?

The oil used to lubricate an electric compressor is not the same as that used in a conventional one. According to Kelvin Butz, vice president of marketing and technical services for RTI Technologies, Inc., "To understand the importance (of using the correct oil), one must visualize what's going on inside a high voltage compressor. The windings in these compressors become immersed in lubrication oil. To prevent electrical leakage, this oil must be of the type that prevents electrical conductance."

According to a Denso spokesperson, a manufacturer of electric compressors for both the OE and aftermarket, the mixture of PAG and R134a refrigerant is conductive. Hybrid vehicles are designed to detect any "shorts" in the electrical system. This can set DTCs and shut down the power to the compressor and the vehicle.

Butz adds, "Today, all hybrid systems utilizing high-voltage electric drive compressor systems have sensors within the system to determine the level of electrical conductance potential. If this level is exceeded, vehicle shutdown will occur."

Are we talking about enough of a conductance to cause physical harm to the customer or the tech? Possible but not likely, according to a Toyota tech I spoke with. When PAG oil is introduced accidentally, it typically results in just enough conductance to trigger an HV system shutdown. Problem is correcting the situation once it's happened. Typically, the system has been running and the contaminated oil has circulated its way throughout the system resulting in an expensive repair bill.

So, just make sure you grab the correct oil bottle, right?

Not quite.

How Does PAG Get In?

PAG oil is usually introduced into an electric A/C compressor by the technician (unknowingly) by means of the shop's recovery/recycle/recharge (RRR) machine. Most of us are used to using the RRR machine's oil injection feature to add oil to a repaired system, and remnants of that oil remain in the service lines and machine's plumbing. No big deal when you're working on conventional systems all day long, but when you connect that same machine to a POE system, enough PAG can be introduced to cause contamination. The new SAE J2788 High-Voltage addendum lists a cross contamination of 1,000 parts per million (0.1 percent) as the acceptable limit, so you can see it doesn't take much to cause a problem.

This same standard also sets the criteria for certifying a new RRR machine for use on a POE system. Service equipment meeting this standard's addendum must not be equipped with oil injection capability, and must include a service line flushing procedure that will meet the cross-contamination limit. That kind of answers a question I know many of you are thinking. What do I do with the machine I just bought?

If you haven't used the oil injection feature, you still don't have the capability to flush the lines between vehicles and there could be enough there accumulated over time to cause you problems. If you have used this feature, don't even think about connecting it to a system using an electric compressor. Likely scenario would go something like this. You complete your servicing on your customers hybrid, and off she goes to pick the kids up from school. By that time, the oil has circulated through the entire system and the PAG contamination triggers an HV shutdown. Now her car won't start, and the car is towed back to you.

According to many manufacturers, the only repair is to replace the entire system. Guess who's paying for that? There is some good news, though. Some makers of RRR machines certified to the base J2788 standards will be offering refits to bring them into compliance with the High Voltage addendum (but may require that an authorized service center perform the upgrade). If this is the season you were considering an upgrade, there are RRR machines offered that meet the hybrid requirements and are more than capable of servicing all R134a systems.

That's Not All

"Certain oils possess higher hygroscopic capability, or the ability to absorb and retain moisture, than others. The moisture in the compressor oil provides the path for electrical conductance," says Butz. Both PAG and POE oil are hygroscopic, POE less so than PAG. So even if you are using the right type of oil, it is imperative that it be from a sealed container to insure that moisture hasn't already made its way in.

And not all POE oils are created equal.

"We've tried to establish an SAE standard for POE oil for use in electric compressors without success," says Ward Atkinson, chairman of the SAE Interior Climate Control Committee.

The OEs are hesitant to sign on unless there is some type of third party testing and verification that an aftermarket offering meets the required specifications for a given manufacturer.

"Just because it says on the bottle that it meets the specification, doesn't mean it really does meet that spec," Atkinson warns. He adds the recommendation to only use OE-branded compressor oil purchased directly from your local dealer asking, "is it really worth your liability to be wrong?"

On the subject of oil, Atkinson also shared that an increasingly common service issue on all compressor designs is over-oiling the system. Late-model compressors are designed to retain most of their oil supply rather than circulate it all through the system, and are using smaller total capacities. Consider the impact of adding only one ounce extra oil into a system that only holds four to begin with. That's a 20 percent overcharge!

Excess oil, at the least, reduces system efficiency by coating the interior of the heat exchangers (evaporator and condenser) and at the worst, can result in compressor lock-up. The use of independent oil injection equipment is now actively promoted by organizations like SAE and MACS to reduce over-oiling and the resulting component damage it can cause. And you've heard me say this many times over. Always follow the OE service procedures for the specific vehicle you are working on.

What about dyes? Good question. Adhere to the OE guidelines on that one. Some come equipped with dye from the factory, some makers will tell you absolutely no dye allowed. The risk here is the similar to what we've been discussing. First, is the dye in a PAG base? If it is, forget it. The other issue is over use of the dye. Will the charge overfill the system?

An Alternative?

While today's topic is focused on keeping the wrong oil out of an electric compressor, there are worse things that can be ingested into any A/C system and/or the RRR machine that it is connected to. Motor Age has long supported the SAE and MACS stand that every incoming car should be checked for refrigerant type (mandatory for new HFO1234yf servicing) and for the presence of certain types of sealant additives.

A product initially designed to filter sealants out of recovered refrigerant is the AirSept Charge Guard. This tool was discussed in last May's Motor Age/TST webinar (which you can view at your leisure in the AutoPro Workshop online) and is a filter-separator that can be mounted to your existing RRR machine or hung from the hood during service. It uses a heater to vaporize the recovered refrigerant so any oil trapped in the gas is free to be captured by the filter.

According to Paul Weissler's report in the May 2010 issue of the MACS Service Reports, Intertek (an industry leading test lab for A/C equipment) tested the Charge Guard using the same standards and procedure as the High Voltage addendum calls for in RRR line flushing. The Charge Guard exceeded the 1,000 parts per million requirement, achieving 104 parts per million or 0.01 percent. Some OEs, though, are not convinced so the decision to go the Charge Guard route is up to you. Keep in mind the product has to be maintained to be effective. But considering all the potentially nasty stuff you can suck into your service equipment, it could very well be worth the investment for that reason alone.

Final Thoughts

Considering servicing an electric compressor system? To insure your safety and protect yourself from unnecessary liability, consider the advice shared with Motor Age by RTI's Butz:

1. Use a certified SAE J2788H machine only. Do not utilize a machine that has on-board oil injection.

2. Perform the hose flush routine in accordance with the machine's operating instructions before connecting to a hybrid. Don't assume it was already performed by someone else."

3. Follow the equipment manufacturer's operation instructions completely for the A/C service. Do not take shortcuts.

4. It is critical to inject the exact compressor oil specified by the OEM using an independent, sealed style oil injection tool.

5. Do not over-inject the amount of oil going back in the system.

As with any other system on a modern automobile, there is less room for error than what we may have grown up with. Stick to the published procedures and recommendations, get the training you need to succeed, and embrace the idea of adding hybrid A/C service to your shop's offerings.

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