In many parts of the country, A/C is a necessity in a vehicle during the summertime. Of course, automotive A/C systems can suffer the same issues that affect residential HVAC systems, including refrigerant leaks. As a mechanic, it’s important that you are able to quickly identify refrigerant leaks in the air conditioning system, so that you can repair the problem, recharge the system, and get your customer back on the road while ensuring that they stay safe and comfortable. There are actually several ways that you can identify an A/C system leak, as well.

The Legalities

Before we go any further, it’s important to understand that the US Environmental Protection Agency (EPA) mandates that anyone working on a motor vehicle air conditioning system (MVAC) in any capacity be certified. If you are not trained and certified, you should not be working on A/C systems. It’s as simple as that. Now that we’ve gotten that out of the way, let’s talk a bit about the various leak detection methods available to you.

Necessary Equipment

While we’ll discuss several leak detection methods, you’ll need some basic equipment for all of them. Perhaps the single most important one is an A/C evac/recharge machine. If you don’t have an A/C machine, there is little point in attempting to locate the leak, as you will not be able to repair it properly. You’ll also need to make sure you have plenty of PAG oil, as well as refrigerant.

Use Your Eyes

Perhaps the simplest, fastest, and most commonly used leak detection method is simply to use your eyes. A visual inspection of the car’s A/C system should give you plenty of information about the presence of any leaks, particularly around the condenser. This is because of the PAG oil that must be included with the refrigerant. When a leak develops, the PAG oil will usually discolor the surrounding material. This is particularly visible on the condenser and the compressor, but you should also be able to spot it in other areas. A visual inspection can also show you physical damage to A/C lines, such as punctures and ruptures.

Check the Pressure

Check the pressure in the system. If it is low, there is most likely a leak. If the pressure is only a little low, you can attempt to recover the refrigerant and then recharge the system to the proper pressure. There is a chance that it was low naturally, without an actual leak. However, if it is substantially low, or the pressure drops again after recharging the system, then you definitely have a leak on your hands.

Use a Detector

Perhaps the fastest way to find a refrigerant leak in a customer car is to use a refrigerant detector. It looks a bit like a hair dryer with a flexible tube at the front with a special sensor on the end. Using a detector is pretty simple – just follow these steps:

  • Make sure the A/C system is at full pressure (evac/recharge if necessary)
  • Turn the detector on
  • Hold the tip near likely leak locations, such as the condenser, along the A/C lines, and around the compressor
  • If the detector alarms, then you have found your leak

Don’t have a detector at your shop? Don’t worry. There are several other ways to spot an A/C system leak.

UV Dye Test

One of the most common ways to identify A/C system leaks is to use a UV dye test. All this requires is the injection of a special UV dye during the evac/recharge process. Once the system is up to normal pressure, crank the car and run the air conditioner. Then, using a special UV/black light, scan for visible dye. There are a few common areas where you might want to focus your attention, including:

  • Compressor hose manifolds
  • Periphery of all fittings
  • Pressure switch front seal and O-ring on the compressor (if applicable)
  • Hose crimps/fitting connections
  • Schrader valve
  • Condenser (damage including pinholes)

Soap Bubble Test

If you don’t have a detector and you don’t have a UV dye kit, there is still another way you can check for A/C system leaks. It’s low-tech, low-cost and pretty effective. All you really need is a way to recharge the A/C system (you should have an A/C evac/recharge machine in the shop), a spray bottle, some water and a bit of dish soap.

First, make sure the A/C system is up to full pressure. If necessary, recharge it before checking for leaks. You’ll also need the engine running and the A/C system in operation (compressor cycling). Fill the spray bottle with water and soap and then spray around the A/C system components. Watch for bubbling, which will indicate a leak.

Once you identify where the leak is, you can repair the problem and recharge the system. Note that this method takes much longer than using a refrigerant detector or using a UV dye kit, but it does work. You may have problems identifying leaks around the evaporator, and around the front seal on the compressor, though.

In the End

As you can see, there are several possible ways to check for an air conditioner leak in a customer’s car. These range from low-tech to high-tech, but they can all be effective. With that being said, the best option in terms of saving time and effort is just to purchase a leak detector (or sniffer, if you prefer). They’re simple to use, pretty accurate, and available through most part suppliers and tool trucks.

Of course, don’t forget your best leak detection tool – your eyes. Always perform a visual inspection before or in conjunction with other leak detection methods. Being observant is your best bet at spotting a refrigerant leak quickly. Familiarize yourself with what PAG oil looks like as it seeps out of a small leak so that you know what you’re looking for.


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