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Hybrid A/C service

Make a mistake on one of these and you could leave customers stranded with a hot vehicle that won't start.

electrical Hybrid A/C A/C service air conditioning hyrbids repair shop training technician training A/C training automotive aftermarket

Summer is approaching fast, and it's time to prepare for the upcoming A/C service season. Perhaps an inventory is going on at your shop. What new vehicles will we be required to service this year? What new equipment will we need? Do we need to adopt new procedures? These are all important questions, ones that need to be considered carefully as an automotive shop owner charts the course to profitability. Making a living in automotive service is about generating revenue, but it's also about minimizing risk. Threats abound and every job that comes in the door has its own pitfalls. For shops that do a good deal of air conditioning repair, you probably have an idea of what kind of work you like to do. You've got adequate equipment, training and maybe even parts for these jobs. We're talking about the kind of work that you know you can make money on. The trouble comes when you take in work that is outside your comfort zone. These are great opportunities to broaden your experience, but the best lessons are often expensive. It's tough paying the bills when you are getting a steady diet of learning experiences. Air conditioning system service can be very profitable, but new technology will tend to throw a wrench in the works. One good example of this is hybrid-electric vehicle (HEV) A/C systems. While these have a great deal in common with conventional A/C systems, there are enough differences that a shop owner (and technician) needs to be fully aware of what they are getting into. Minimizing risk in this environment is going to involve doing your homework and being able to steer clear of the pitfalls. Training and updated equipment requires an investment of both time and money, but can result in net savings that will bolster the bottom line. Done right, this could make your shop the go-to guys for this kind of service, and presto! You've found a new comfort zone.

Carving out a niche in hybrid A/C service starts with a thorough knowledge of what makes these systems unique. Let's take a look at the basics of hybrid air conditioning systems, and then go over some important points to keep in mind when servicing them.

Electric-drive Compressors

The original HEVs that were sold in the U.S. (e.g., 2000 Honda Insight, 2001 Toyota Prius) had A/C systems that utilized a conventional belt-drive compressor. This kept things simple, but left much to be desired regarding fuel efficiency. For example, most hybrid-electric vehicles are designed to shut off their internal combustion engine (ICE) at stoplights and in traffic jams. This process (called idle stop) often was altered or suspended when the vehicle air conditioning was in operation, because the ICE had to be running for the A/C compressor to do its job. To get around this problem, engineers designed A/C compressors that were driven by electric motors. This was first seen in the 2004 Toyota Prius, which used the Denso ES 18 compressor that was powered by three-phase alternating current. Now, the HEV high voltage (HV) battery could be used to power the compressor through an inverter and the vehicle's idle stop function would not be impaired. Beyond that, it was now possible to run the compressor at the most efficient RPM for any mode of operation, completely independent of ICE speed. A further benefit was that air outlet temperatures and humidity levels were easier to regulate, increasing overall passenger comfort.

Not all of the new compressors were thoroughbred electrics. Honda utilized a Sanden compressor with two separate compressor scrolls and a common inlet and outlet. The primary scroll is belt-operated, while a smaller-displacement scroll is driven by a high-voltage electric motor. The belt-driven scroll operates like any conventional compressor, shutting off whenever the ICE goes into idle stop. At this point, the electric-drive scroll is able to keep the A/C in operation until such time that the ICE restarts. This system works well for the Honda hybrids, which are more reliant on the ICE than Toyota's Prius.

Other HEVs that were first built with belt-drive A/C compressors include the Ford Escape hybrid, which was redesigned with an all-electric unit for the 2010 model year. The Ford Fusion hybrid (introduced in the 2010 model year) also uses an electric A/C compressor. It would appear that a trend is in place, perhaps setting the stage for a migration of this technology into non-hybrid vehicles.


A primary issue to be dealt with when servicing hybrid A/C systems is how to prevent contamination with polyalkylene glycol (PAG) compressor oil. Electric compressor windings are immersed in oil, and only polyol ester (POE) oil is able to protect the insulation on the windings and prevent electrical leakage. OEMs have strict specifications regarding the oils to be used in HEV A/C systems, and they make it abundantly clear that even small amounts (as little as 1 percent) of PAG will damage the system permanently. Past that, the lower insulation resistance of PAG will lead to what is effectively a short-to-ground in the compressor. This represents a potential shock hazard to the technician and will cause DTCs to be generated as well as a possible no-start. The problem, of course, is that virtually all non-hybrid R-134a systems use PAG oil, and your shop's recovery/recycle/recharge (RRR) machine will most likely have residual PAG in its hoses and other passages. Left unchecked, this leftover PAG will contaminate a hybrid A/C system and may require replacement of all major A/C components. Since we're on the subject of minimizing risk, how about we discuss ways to prevent this from happening to you?

The first possible solution is having a dedicated RRR machine and/or manifold gauges for servicing vehicles with electric-drive A/C compressors. If you are a high volume shop with a good deal of hybrid A/C work coming through, this might work. However, the majority of shops will not be able to justify the cost involved in taking this path. Past that, there is always the possibility of having a technician use the wrong RRR machine on an HEV anyway. As Mr. Murphy stated so eloquently, "If anything can go wrong, it will."

Another approach would be to purchase an RRR machine that has a hose-flushing feature. Prior to vehicle service, the high and low-side service hoses are attached to ports on the machine and the technician commands it into the hose flush mode. Refrigerant is circulated through the hoses and residual compressor oil is removed from the lines, preparing the machine for the next vehicle. The specified compressor oil would then be injected using the RRR machine, which would not have a significant amount of old oil in it to contaminate the new charge. The previous method will certainly minimize the risk of contaminating an HEV A/C system with PAG oil. However, this might not be sufficient insurance for the most cautious shop owner. For those who don't want to take any chances, the best approach is to recharge an HEV A/C system through a filter/separator that will remove any residual oil and particulates from the refrigerant stream. Once the system is recharged, compressor oil can be installed directly using a manual inject tool. This takes the RRR machine out of the loop as a potential source of PAG contamination and allows the technician to use the machine normally on non-hybrid vehicles.

Leak Detection

A major part of any A/C technician's job description is to find and repair refrigerant leaks. This can be a time consuming process, and only seems to get more challenging as systems become more tightly integrated on the vehicle. Another complication is that A/C system refrigerant capacities are decreasing as automotive engineers figure out how to do more with less. This means that even trace leaks will have a significant impact on system performance. Certainly, this is the case on hybrid vehicles and technicians are always looking for a leg up to help them find those nagging slow leaks.

The use of fluorescent dye in A/C systems has been a huge help over the years. The use of dye for finding refrigerant leaks is a mainstream practice, where even OEMs install dye at the factory to help dealership technicians with warranty repairs. It hasn't helped that Toyota and Honda have both issued prohibitions on the use of dye in their hybrid A/C systems. The reasoning behind this is not clear, especially when a number of aftermarket companies make dye products designed specifically for electric compressor applications. It is also noteworthy that Ford installs dye in their HEV A/C systems, although their methodology is different. Ford places a dye "wafer" in the receiver-drier's desiccant bag, which dissolves once the system is in operation. Ford is very clear that liquid dye is not to be added to these systems. If a technician wants to add more dye, a new receiver-drier (with a fresh dye wafer) is to be installed.

The issue could be about the composition of the dye itself, but it may have more to do with the liquid it is dissolved in. If you have a liquid dye product that you use at your shop, it is quite likely that it is PAG-based. It will pay to do some more investigation on that, because some technicians might assume that the liquid dye they are using is dye only. This could be an expensive assumption to make, especially if some PAG-based dye gets installed in an A/C system with an electric compressor. Regardless, the lowest risk approach in HEV A/C leak detection is to go with an electronic leak detector. Many new leak detectors meet the latest Society of Automotive Engineers (SAE) standards for detection, and if used properly, will detect even the smallest of leaks.


There are unique challenges when performing hybrid A/C service. However, a savvy shop owner will take steps to limit their risk by getting the right training and equipment to get the job done right. Good luck and here's to a profitable A/C service season!



Both PAG and POE compressor oils are highly hygroscopic, meaning that they have a tendency to absorb water (much like brake fluid). The attraction is so powerful that the oil can absorb moisture through the pores of a thin plastic container, which explains why hybrid A/C oils are often shipped in metal cans. This property can complicate matters on a service level, because opening a container of POE immediately starts the oil on a rapid downhill slide in terms of its quality. Experts advise that if a container of POE is opened and only a small amount of the oil is used right away, the remainder should be discarded to prevent contamination. This is where having small (one or two-ounce) packages of POE available can reduce waste and improve the level of service for your hybrid A/C customers.


General A/C Service Tips

The experts at Delphi offer the following tips for general A/C service. While not specifically targeted at hybrid applications, these basic rules are good for any A/C technician to keep in mind.

When installing a replacement A/C compressor, be sure to perform the oil balance procedure as specified in the instructions provided with the new compressor.

Leave shipping caps in place on a new compressor until such time that the refrigerant lines are being attached.

Do not lubricate seal washers in the system, such as those used to seal refrigerant lines to the compressor. However, O-rings should always be lightly lubricated with mineral oil (even on R-134a systems – DO NOT use PAG).

Always use lint-free gloves or bare hands when assembling refrigerant lines. Lint has been identified as a common cause of refrigerant leaks. 
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