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A/C servicing — are you doing it right?

Wednesday, May 1, 2019 - 07:00
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Speaking of new machines and new refrigerants, it was brought to my attention at the recent Mobile Air Conditioning Society (MACS) conference that many of you are using R134a machines modified to recover R1234yf. I cannot stress how wrong that is, and I don't blame you guys since many of you purchased the refits from "reputable" sources. It is a pure matter of safety that you cease and desist today!

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We all know that R1234yf is "mildly flammable" and there are certain safeguards built into machines certified to the proper SAE standards for servicing these newer systems that the old R134a cabinets simply do not have. Another big difference is the R1234yf machine's requirement that a refrigerant identification test be performed prior to evacuation and recovery of the vehicle's charge. Are you doing that prior to pulling in the charge on that retrofit machine?

Considering that you'll be servicing R134a systems for some time yet and the number of vehicles you'll see fitted with R1234yf will just keep growing, bite the bullet and invest in the proper equipment to do the job.

Finding those lost dollars (leaks)

Locating and fixing even the smallest system leaks is also more important; in part, due to the high cost of R1234yf. It's also critical due to the lower system capacities. As I've already noted, even a 10 percent drop in charge will impact cooling capabilities and oil flow through the system.

(Photo courtesy of Tracer Products) Many new cars come with dye from the factory so check before adding any additional dye to the system. If you do add, add 1/4 ounce only to avoid "overdosing" the system.

The most commonly used leak detection method is fluorescent dye, so allow me to offer a few notes on its use. First, it may take a bit longer for dye to circulate through the system than it used to on some models. If you've fixed the big leaks and want to make sure you got them all, ask your customer to return after a few days for a recheck.

It also helps if you match the UV light you're using to the dye and wear the yellow lenses that the dye maker includes with their detection kit. Yes, UV lights operate in a range of frequencies and the dyes can also vary from maker to maker.

To make the dye easy to see, use a UV light recommended by the dye manufacturer. For best fluorescence, the two should be matched

Also, be aware that many manufacturers are adding dye at the factory. It's not going anywhere unless there's a leak so check to see if dye is already in the system before adding any. If you do add some, add only 1/4 ounce to the system. With the lower oil capacities of today, it is easier than ever to overdose the system with dye if you use too much.

A neat tip I also learned at the MACS event (in a class taught by Standard Motor Products' Peter McArdle) may be helpful when you suspect that small leak is in the evaporator core. Park the suspect vehicle in the sun and close up the cabin nice and tight. The idea is to build up the interior heat level to raise the pressure of the refrigerant in the evaporator core and to give the oil that may be coating the interior surfaces of the core to fall to the bottom. The heat increases the pressure of the gas, too, making it easier for the gas to escape.

After the vehicle has sit for a few hours, take a Styrofoam cup and place it under the evap drain tube prior to starting the car and turning the A/C on "max cold". The idea is to capture the first droplets of the water condensing on the outside of the evaporator in the cup. Now use your UV light to look for dye.

The sniffer couldn't detect the leak since the refrigerant was trapped under the protective sheathing but after letting the system run for a while, the dye became obvious.

You can also use your sniffer to check for the captured gases in the evaporator case by sticking it up in the evap drain line prior to start up. Since refrigerant is heavier than air, the fumes should collect in the bottom of the case. On some cars, removing the blower motor resistor allows access to the base of the evaporator as well.

On the high side, hose leaks right at the hose crimps are common. To help you find those stubborn ones, get the system pressures high by running the system for a while and then checking for leaks immediately after shutdown. An option is to use the same tactic I discussed when trying to coax out every last ounce of refrigerant - preheat the system by closing the hood and running the engine until it reaches normal operating temperature. If you live in a warm climate, simply putting the vehicle out in the sun for a while may be enough to push up system pressures and reveal the leak. All of these are techniques you can try using the service equipment you likely already own.

Yes, the fundamental principles that allow us to keep our customers cool in the summer and warm in the winter haven't changed. But the way we have to service these systems to keep them at their peak efficiency has!

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