Working on today's mobile A/C systems

Jan. 1, 2020
In my early days as a technician, air conditioning was an expensive option and the exception rather than the rule. Now it seems it's harder to find a car not equipped with air than one that is. And these systems are more efficient, utilizing smaller

Mobile air conditioning systems are becoming more precise and less forgiving.

underhood mobile a/c service mobile air conditioning air conditioning service mobile refrigerants vehicle technology repair shop training technician training A/C training automotive aftermarket In my early days as a technician, air conditioning was an expensive option and the exception rather than the rule. Now, it seems it's harder to find a car not equipped with air than one that is. And these systems are more efficient utilizing smaller refrigerant charges and lasting longer than their predecessors. Proper servicing of these systems is vital to maintaining that efficiency and longevity.

Before You Begin

Before you stick a thermometer in the dash vent or open the hood to connect your recovery-recycling-recharge (RRR) machine, you'd better grab your wallet and make sure there is an approved EPA Section 609 certification card in there. According to federal regulations, anyone servicing or repairing motor vehicle air conditioning systems "for compensation" must be certified in the proper use, reclamation and disposal of refrigerants. Further, you must be able to produce these credentials should anyone with a badge ask for them.

Many of you were certified years ago, and that certification is still good providing you can produce the paperwork. If you can't, there are a few organizations that can help you recertify and stay legal. The Mobile Air Conditioning Society Worldwide (MACS) is one source of Section 609 testing and certification, and so is ASE. Visit either organization on the Web for more information.

Shop owners have some EPA rules to follow of their own, including registering the fact they have approved RRR equipment and some other record keeping requirements. MACS and the EPA can both help you make sure that you are following all the applicable rules and keep you out of trouble.
Keep in mind that EPA certification only means you have a basic understanding of "best practices" and the safe handling of refrigerants. MACS, however, does offer specific training programs to help you build that expertise and, of course, ASE certification A7 is recognized as one standard measure of your actual service and repair knowledge. Motor Age Training's A7 study guide is an excellent tool in both preparing for the A7 exam and sharpening your heating/air conditioning repair skills.

On to the Car

It typically starts with a "the car isn't getting cold" complaint, or something very similar. As with any other customer problem, the first step is to verify the complaint. As you bring the car into the shop, note where the customer has set the heating/ventilation/air conditioning (HVAC) controls. Once in a while, the complaint is simply a matter of the customer's not knowing how to set the system for maximum cooling.

Next, adjust the controls for just that, maximum cooling: fan on high, recirculation mode on, temperature to its coldest setting and airflow adjusted to the center vents. Then verify all that is happening. Is the blower speed adjustable throughout its range? Can you hear the recirculation mode door closing, or sense the change in airflow? Does adjusting the temperature from "full cold" to "full hot" make any difference? Can you shift airflow from the center, to the floor and defrost, and back again?

Any fault found so far should be noted on the repair order, and looked at more closely once you have the car in the bay. Sometimes it's not a matter of an A/C system that isn't working effectively, but the distribution of that cooler air to the car's cabin that's to blame.

For the moment, though, let's say everything inside the car is working as it should. The next step, then, is to verify compressor operation. With the car idling, open up the hood and look to see if the compressor is engaged. This isn't as easy as it once was, my friends! If the compressor is a conventional design, using a magnetic clutch, then a visual inspection is usually enough to see whether or not its spinning. But if the car is a hybrid using an electric compressor, or one of several models using a constantly running, variable displacement compressor, you'll have to do a little more than just look at it! It is always a good idea to spend a few minutes reading the theory of a system's operation before you start working on it, especially if you've never worked on that particular car before.

So make a grab for the low pressure line leading out of the evaporator next. How cold is the line? Even if a conventional compressor is spinning, it doesn't mean there is any pressure being built in the system. Compressors are little pumps or engines if you will — low compression resulting from internal damage or busted reed valves will keep a car from getting cold as much as a low refrigerant charge will.

If your visual inspection hasn't given you any particular direction, then it's time to hook up the gauges. Wait a minute. You aren't using the gauges on the RRR machine, are you?

Protect Your Equipment

That RRR machine you're using likely cost your boss a few thousand dollars. It would be a shame to ruin it by connecting to a car with contaminated refrigerant. Counterfeit blends are being sold in the U.S. every day, and many DIY sealants can clog your machine's arteries as quickly as fast food burgers can clog the ones going to your heart.
Identifiers are available with a variety of options, beginning with simple go, no go machines that will set you back about $500 new. Nearly every identifier made for use in the U.S. market is manufactured by Neutronics, no matter the branding on the package. Neutronics also manufacturers a sealant identifier that induces a small leak in the high side of the system, with the idea being that if that leak seals there must be a sealant additive in the car — something you don't want in your RRR machine. (At the time of this writing, Neutronics has completed the development of an identifier for use on HFO1234yf systems. See the related feature in this issue for more info.)

If your shop doesn't own a refrigerant identifier, make the investment in order to keep the source tank in your RRR machine clean and pure.

The Three Rs

Recovery, recycle, recharge — the three Rs. Most of the air conditioning problems I've dealt with were centered on an improper charge, which often could be traced back to the last tech that worked on the car. Low system charges impact oil flow through the system and overcharged systems cause high head pressures and temperatures. Both can quickly cause the death of an otherwise healthy compressor. The trend in newer systems is to do more with less, so system charges are getting lower and lower and that means their tolerance for improper evacuation and recharging procedures is becoming less and less. The Toyota Yaris, for example, has a total system capacity of only 11 ounces of refrigerant!

You probably already are aware that there is a new standard for RRR equipment, specifically SAE J2788. These machines are much more accurate in all phases of operation than their predecessors. That can mean savings to you in time and materials, so if you're in the market for a new machine, insist on one meeting this standard. If your budget says you use the older machine this season, then here are a few tips to help you get the most out of it.

First, make sure your machine is as healthy as it can be. Change the oil in the vacuum pump, and replace the filter(s). Make sure your source tank has nothing but clean refrigerant in it, all the air is being purged from it on a regular basis and that the scale it's sitting on is accurate. Keep in mind that many older RRR machines have a larger margin for error when the source tank is below a certain weight.

During the recovery phase, allow the machine to sit idle for at least five minutes, and then check the gauges for any pressure reading. Refrigerant that is trapped in the oil will take some coaxing to remove, but it is critical that you remove all of the existing charge in order to insure the correct recharge is accomplished. Repeat the recovery/sit cycle until the gauges show no pressure build up in the system, or better yet, the system remains in a slight vacuum.

I can't count the number of times I've witnessed techs charge a repaired system without first performing a thorough evacuation and vacuum. You already understand that the idea of putting the system into a vacuum is to remove and moisture in the system, so there's enough reason to perform this procedure. Want to guess what else is wrong with this picture? If you said there's now air in the system, you'd be absolutely right! If the system had been opened for repair, air would have entered as soon as the line was unbolted. Air will cause system pressures to be high and cooling effectiveness to be low. Always vacuum down the system and allow it to sit in vacuum for at least 30 minutes before recharging. Personally, I like to wait an hour but then again, I live in a very humid climate and have been known to go a little further than I may have needed to in order to be sure of my fix.

What about Oil?

When recovering refrigerant, there should be very little oil removed from the system. Most of the oil I find in the machine's recovery bottle comes from oil trapped in the lines from using the injection feature on the machine. Let's see, no one has ever injected an entire system oil charge using the machine, have they? And then forgot to purge the lines? Instead, follow the OEM procedures for correcting the oil quantity after a repair.

Type of oil for R134a is easy enough. You must use PAG oil on these systems, right? Well, kind of. PAG oils are available in three different weights so it is important to use the oil recommended for the car. If replacing an OEM compressor with an OEM part, follow their oil recommendations. If you're using an aftermarket compressor, follow the oil specification provided by the manufacturer of the compressor. And let's not even get started about high voltage electric compressors. No PAG for them! Use POE only to avoid even the smallest possible of causing a high voltage leak.

Speaking of compressors...

When replacing a compressor, remember that any oil in the replacement is strictly there for shipping and storage purposes. Remove that oil and add the appropriate amount of the specified oil. Too little will have the expected results of destroying the replacement compressor in short order, and too much will coat the insides of the heat exchangers and reduce system efficiency. Treat the addition of dyes as you would oil. While many DIYers may think that more is better, professionals like you know that is definitely not the case. Install the compressor and lines, then rotate the compressor assembly several rotations by hand to insure the inside workings of the compressor are nicely coated before start up.

The basics of servicing and troubleshooting today's HVAC systems remain the same, but the tolerances we work by are tighter than ever before. It is imperative that you follow listed service procedures, perform the RRR process correctly and treat the system's lubrication as seriously as you would the engine's to insure a professional repair.

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