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Finding and repairing leaks in air conditioning systems

Monday, May 1, 2017 - 07:00
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The daily work routine of the automotive technician is mostly taken up with fixing leaks. Think about this for a moment; when we work on cars, we are spending the lion’s share of our time finding leaks and then repairing them. This could be air, vacuum, coolant, oil or even electricity. Obviously, the better we are at pinpointing leaks, the better we serve our customers and the more money we can make.

Mobile air conditioning systems operate by circulating refrigerant through a sealed system, and will stop working if the refrigerant leaks out. Generally speaking, these systems work very reliably so long as the refrigerant stays put. However, the majority of the problems we see are related to refrigerant leaks, and these can often be challenging to locate. There are multiple techniques for finding A/C leaks, and each has its own merits and pitfalls. Having said that, you will probably want to have several of them in your diagnostic toolbox to stay ahead of the game. Again, increased expertise in finding refrigerant leaks will help your customers stay cool and put more money in your pocket.

One of your first checks is to determine whether there is dye in the system.  Take off the low side service port cap and look for dye residue with a leak detection flashlight.

The A/C service season is coming up fast, and many of us haven’t had to deal with an air conditioning performance concern in several months. We may be a little rusty with the basic rules of refrigerant leak detection, and a review of technologies and techniques may be helpful to get us off to a good start. If your shop does air conditioning repair, having your technicians go over the information in this article could flatten the learning curve and get you off to a great start on a profitable summer A/C service season.

Getting underway

Let’s say that you are an automotive technician and the first A/C performance concern of the season has appeared in your bay. You suspect that the system is low on refrigerant and you will need to locate and repair one or more leaks. One of your first questions should be: Is there dye in the system? Look for a sticker in the engine compartment that indicates that dye has been installed. If you don’t find a sticker, take the cap off the low side service port and shine your leak detection flashlight over it. Glowing dye residue inside the port changes your whole approach, because now you can go directly to inspecting the system with your flashlight.

We’ll assume you don’t see any signs of dye in the system. You don’t have to install it right now, just be sure that you get it done before you return the car to the customer. Be sure to use a high-quality dye that meets SAE J2297 standards. It pays to take some precautions at this point, because it is easy to make a mess when connecting to the service port due to pressure in the A/C system. Cover the coupler with a rag during this process to prevent splatter and extra work cleaning up after the fact.

(Courtesy of Inficon) A quality electronic leak detector will pay back dividends.  Remember that these require periodic maintenance, so follow the instructions in the operator’s manual

Approximately ⅛ ounce of dye concentrate will work for anything from passenger cars to a heavy duty truck. Don’t overdo it, one trigger stroke on most injectors will get the job done. Don’t assign the cost of the dye to your shop materials fees! Put a separate line item on your invoice for the dye you install in your customer’s vehicle. Take some time to fill out a sticker indicating that there is dye in the system and install it in the engine compartment. Obviously, this is not going to help you with finding the leak right now because it will take some time for the dye to circulate with the refrigerant oil and make its way through the leaky joint. Having said that, your next step will be to get out your electronic leak detector and go over the entire system slowly and carefully.

Electronic leak detection should be done in the shop with any fans turned off that could cause air movement around the area you are testing. Turn on the detector and let it warm up for a minute or two. Turn the sensitivity switch to HIGH, and place the sensor probe about ¼” from the possible leak source. Slowly move the detector underneath the connections and lines you are checking at a rate of about 1 to 2 inches per second. When the detector beeping rate increases, pull it away for a moment to extinguish the alarm, then place it back near the same area to verify the leak. To pinpoint the location of a larger leak, turn the sensitivity switch to LOW and retest. When you locate a leak, continue on and inspect the remainder of the system. It is always a possibility that you have more than one leak to deal with.

(Courtesy of Inficon) With the sensitivity switch on HIGH, keep the probe ¼” from the work and move it slowly, about 1-2 inches per second.  Remember that antifreeze, Loctite, and windshield washer fluid can cause false alarms
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