Finding and repairing leaks in air conditioning systems

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

Thomas Parker of Inficon Inc. shares some tips for improving your results when using electronic leak detectors. First, be aware that false alarms can be caused by windshield washer fluid, antifreeze, and Loctite, so be sure to avoid these fluids when leak testing. The technician should also be aware that the filtering software in some detectors is more effective than others, so spending extra money on a quality detector can pay dividends. Also, keep in mind that all electronic leak detectors require maintenance, so be sure to follow through on the instructions in your unit’s operator manual.

Live and let dye

One disadvantage with electronic detectors is that they will not detect leaks that only take place during vehicle operation. This is where leak detection dye excels, because it is dissolved in the system oil and will travel with the leaking refrigerant where it can be detected when the vehicle is in the shop. It can also be effective for locating leaks in areas that are visible but cannot be accessed by an electronic detector.

(Courtesy of Spectronics) If the system doesn’t have leak detection dye installed, be sure to inject 1/8 ounce of dye concentrate before returning the car to the customer.

If the system had dye in it when it came to you, you can immediately perform an inspection using a leak detection flashlight. The large, awkward lamps that were once the industry standard are a thing of the past. Compact, lightweight flashlights are now the norm, and these are typically battery powered for ease of use. Keep in mind that there are a number of types of leak detection flashlights available. John Duerr of Tracer Products offers the following tips for choosing a flashlight for refrigerant leak detection:

Fractional vs. single LED — the type of LEDs that are placed in the lamp are indicative of how much power is in the lamp. Fractional LEDs are a set of several small LEDs, while a single LED has 1 powerful lamp. Traditionally, single LED lamps are more powerful and have a better fluorescent response than fractional LED lamps.
Dye absorption — there are three primary types of light used in UV fluorescent leak detection. However, each has a different wavelength and is absorbed differently by UV fluorescent dye.
1. UV (365 nM) is responsive to all dyes.
2. Violet (400 nM) is compatible with all A/C and coolant dye, and some fluid dyes.
3. Blue (450 nM) is compatible with all dyes with the exception of extended life coolant dyes.
Beam profile — how wide the useful light projects on to a surface. A strong flashlight will have a consistent beam, while a weaker flashlight will become dimmer towards the edges of the beam profile.
Construction — flashlights need to be designed to withstand use in extreme heat without failure.

For best results, always wear fluorescence-enhancing safety glasses when using a leak detection flashlight. This will help highlight any glowing dye as well as protect your eyes from UV radiation. It goes without saying that fluorescent leak detection works best in low light conditions, so ideally the vehicle will be indoors with the shop lights turned down.

(Courtesy of Spectronics) When inspecting for dye leaks on an A/C system, start at the compressor discharge and carefully make your way through the entire system. When you get back to the compressor inlet, be sure to inspect the input shaft seal.

Start at the A/C compressor discharge port and thoroughly inspect all fittings and lines as you follow the path of the refrigerant through the system. Be methodical, thoroughly inspecting each component before moving on. If you find a leak, make a note of its location, then continue inspecting the system in search of other leaks. Follow the lines until you make your way back to the compressor inlet. While you are there, don’t forget to assess the condition of the compressor shaft seal.

Verifying Evaporator Core Leaks

So you’ve inspected the components in the system that are reasonably accessible, and you have yet to find a leak. This is where it can get challenging, because it is possible that you have a leaky evaporator to deal with. You don’t want to be guessing in this situation, because it is often a labor-intensive process to remove and replace an evaporator in most vehicles. What can be done to increase our accuracy in diagnosing evaporator leaks?
Jeff Prickett of Stride Tool recommends that you stress the A/C system to help verify an evaporator leak. Leave the vehicle doors open and run the engine with the A/C in MAX COLD and the blower on HIGH. After 15-20 minutes, shut the engine off and place a piece of white paper on the floor beneath the evaporator drain. As the evaporator thaws out, condensed water will flow into the evaporator drain and then on to the paper underneath. Direct your leak detection flashlight onto the paper to reveal dye that has been carried with the water. You will be amazed at how any dye that is present becomes that much more visible with the white paper as a background.

(Courtesy of Spectronics) Once all repairs are complete, be sure to clean up your work with an approved dye remover.

When you find leaks and make the associated repairs, be sure to use an approved cleaning solution to remove all the dye from the leak sites. This will help the next technician (possibly you) from being misled when performing future A/C leak repairs on the vehicle.

Tough cases

Slow refrigerant leaks that are not detectable with dye or an electronic detector will require another approach. Your next step could be to replace the refrigerant in the system with a substitute gas and then test for leaks. The idea is to use a gas that has a smaller molecule than that of the refrigerant, so it will leak more freely than the original. The substitute gas must also be harmless in terms of flammability and its effect on system materials.

One approach is to recover the refrigerant from the system and then fill it with nitrogen. The technician then closes the valves to seal the system and listens for leaks with an ultrasonic listening tool. This can work for large leaks, but will be less effective for the slow leaks that cause us the most grief. What works best is to use a gas that can be detected with an electronic gas detector. Having said that, the two top candidates for substitute gases are forming gas and carbon dioxide.

According to Bernie Thompson of Automotive Test Solutions, carbon dioxide has some compelling advantages for A/C leak detection. While it is a small molecule and will leak more readily than refrigerant, it is also heavier than air and will fall from a leak rather than dissipating. This helps concentrate the leaking gas and makes it easier to detect using electronic means. Automotive Test Solutions’ Bullseye Leak Detector system uses an electronic CO₂ detector as a first step to find the general location of a leak, but then pinpoints the leak using a specially-formulated foam. The pink Leak Seeker foam is sprayed on to the general area of the leak, which turns yellow and produces bubbles when it makes contact with carbon dioxide. FYI - the Bullseye system can be used to detect leaks of all kinds, including slow leaks on tires, EVAP leaks, and head gaskets. This versatility can be very useful to any shop that does general automotive repairs.

(Courtesy of Automotive Test Solutions) Carbon dioxide works very well for A/C leak detection because it is a smaller molecule than the refrigerant and will leak more easily. Start by recovering the refrigerant from the system, then charging it with CO_2.

(Courtesy of Automotive Test Solutions) After finding the general location of the leak with the electronic detector, spray it with the Leak Seeker foam. The pink foam will turn yellow at the exact location.

The bottom line

Slow refrigerant leaks are often the bane of the A/C service professional. While there are numerous technologies available for A/C leak detection, you will be best served by using more than one to get the job done. It goes without saying that you shouldn’t go cheap. Buy the best tools available and provide the training to your technicians so they can use them properly.

There are cascading benefits that will be realized with increased competence in locating A/C refrigerant leaks. Finding and fixing slow leaks reduces comebacks, making for happier customers and more business coming your way by word-of-mouth. Your technicians will also gain on the job satisfaction front, with more flagged hours and fewer comebacks. This all adds up to increased profits as your customers stay cool through the hot summer months!