How to Find a Leak in your AC System using a UV Dye

Over time with age, the components or seals will fail eventually causing a leak for the refrigerant to escape from your car AC‘s system. When the system is low on refrigerant, it’ll either work poorly. If the refrigerant leaks out enough your AC won’t work at all.

It doesn’t matter if it’s winter and you are not using your AC. You must have an operating vehicle at all times. Something as a small refrigerant leak can grow up into a much bigger issue if left untreated. So, in this article, I will show you how to find a leak in your AC system using a UV dye.

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How to Find a Leak in your AC System using a UV Dye

If your AC system is leaking, it is only a matter of question when you will run out of refrigerant. At that point, your AC will either work poorly or not work at all. So, if you have noticed that your AC is not working properly even though you added refrigerant recently, it is possible that your AC system is leaking somewhere.

But where exactly? The first step is adding a dye to the system which will help you pinpoint the leak. Follow the steps and you will learn how to find a leak in your AC system using a UV dye.

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1. Materials needed for this procedure

Before you start with the procedure of finding a leak in your AC system, there are some items that you will need.

  1. UV dye for AC systems (see prices on
  2. UV enhancing safety glasses (see prices on
  3. A UV light (see prices on

2. Locate the low-pressure port

How to Find a Leak in your AC System using a UV Dye

The AC system is filled through the low-pressure port side on the AC system which is found under the hood. It’s a smaller port covered with a cap that may be labeled with an L (meaning low-pressure side). The low-pressure port might not be in the same location in all vehicles, but it looks the same on all models.

3. Connect the refill tool to the low-pressure port

Once you remove the cap, you will find a Schrader valve. You’ll need a special tool to fill up the AC system. For this procedure, I’m using a refill tool that I got from Typically, these are found with a recharge kit, a quick disconnect that only fits onto the low-pressure side, and a gauge to monitor the pressure in the AC system.

It is important to shake the can first before using it. The valve has a punch that is operated by the handle. You need to make sure that it’s fully retracted before screwing on the can. Then, screw on the can.

4. Start the engine and turn the AC on

How to Find a Leak in your AC System using a UV Dye

Start the engine and let it run. Make sure that you have enough fuel to last you at least 30 minutes. Then, turn on the AC. Set up the fan to highest and the temperature to coldest. The AC compressor may not turn on if it’s excessively low. However, if the rest of the system is in proper working order, once you have enough pressure, the pump will cycle the dye through the AC system.

5. Add the dye into the AC system

Safety glasses are highly recommended as refrigerant can cause damage to your eyes. Attach the recharge tool for the low-pressure side of the AC system. Turn the valve in to pierce the can. Then, slowly open the valve and monitor the pressure. This may take a few minutes and shaking the can does help a little with refilling the system.

Constantly monitor the gauge and keep the pressure in the blue area. This is the safe zone. However, depending on your recharge tool, the colors may vary on what is an acceptable pressure range and what isn’t. You don’t have to use the full can, but enough where the pump can recirculate the dye through the AC system.

6. Remove the refill tool and check for leaks

Once you finish with the refilling process, close up the valve and then remove the recharge tool. You’ll want to use a wax and grease remover on a q-tip to clean inside the charge port to remove any dye so we don’t have a false result. Finally, reinstall the cap. Depending on how bad the leak is, you may need to run the system anywhere from an hour to a few days and check back.

For finding the actual leak you’ll need yellow safety glasses as you’ll be unable to see the dye without them and a UV light. The best time to check for leaks is at night. Make sure there are no other lights around. Turn on the UV light and inspect all areas of the engine bay where the AC lines are located such as the compressor, condenser dryer, and even the evaporator.

The condenser might be hard to check and removing the grill may make the inspection much easier. This is a common component for developing a leak from a stone impact. You’ll be looking for a fluorescent area where the dye has leaked out. If you are unable to locate the leak, then, you might have to check the low-pressure cap as it can be the cause of the refrigerant leak.

Car Care Hacks

Hi there. I am a certified Automotive Service Excellence (ASE) mechanic since 2018 and a car detailer for 10 years.

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