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The air conditioner is one of the most complex systems inside a car. There are a lot of moving parts that must work together to keep the interior ice cold.
There’s nothing worse than a hot car in the middle of summer. Living in the South, I know that air conditioning is a necessity for every vehicle owner.
The most common problem I see is leaking refrigerant, which anyone can fix.
Key takeaways
Simple ways to find a leak in car air conditioners
Before fixing an AC leak, finding where it is coming from is vital.
Refrigerant can leak from the aluminum lines, the dryer, or even the coils.
Use a gauge to verify low refrigerant
First, I connect a set of manifold gauges to the air conditioning system to check the refrigerant level.
The ambient temperature affects the pressure reading, but a low side reading of 25 PSI or below means it is low.
If I don’t have a manifold with me, I will grab a can of liquid refrigerant that comes with a gauge from an auto parts store.
I don’t add anything now, but I use the included hose to check the low side.
Visually inspect for leaks
Now that I know the vehicle’s air conditioning system is low on refrigerant, I do a quick visual inspection.
I specifically look for signs of dirt that may get stuck in the liquid refrigerant along the line.
Small amounts of oil or dye may also come out of the air conditioning system and be easier to spot.
Finding a leak by just looking is pretty difficult, if not impossible.
I primarily look at the air conditioning line connections and the high and low side service port.
Soap solution
One option that many people like to use is to look for bubbles with a soap solution. All it requires is a small spray bottle with soap and water.
Then, you spray the lines, and the leak will create bubbles.
I personally don’t like using a soap solution because the chances of it working are low. However, it is a low-risk and low-cost test for people who have no other options.
The problem with using a soap solution is that the car must have a pretty bad freon leak while still having pressure in the system.
Additionally, the leak would need to be easily accessible to even find it.
ACLAB note:
You can use a professional electronic AC leak detector for finding where the leak is coming from.
Use UV dye
A method that I like better than soap is UV dye.
It involves injecting a colored dye into the vehicle’s air conditioning system. Once added, the dye will slowly leak out and be visible.
Several vehicle manufacturers started adding UV dye to the AC system in the last two decades.
In such cases, adding dye isn’t required since it already exists in the line; simply look for a greenish liquid.
UV dye is available at auto parts stores but sold differently. It is available in a liquid bottle that requires a special additive tool.
I’ve also seen UV dye sold as a leak detection kit with everything needed to inject the dye.
While I have the tool, purchasing it in a syringe or a pressurized can is sometimes easier, so I can add it without needing other hoses or adapters.
Like the soap solution, the biggest problem with the UV dye method is that the AC system must have refrigerant. The dye must run in the pressurized system to be visible.
I try to let an AC system run between 20–30 minutes after adding the dye before looking for leaks.
If the leak isn’t visible under the hood, I try to look at the condenser coil.
Black light
One good thing about the UV dye method mentioned above is that I can turn on a black light to help find the leak.
A UV light illuminates the dye, which makes it easy to spot.
A black light is great for finding small leaks or holes in the coils where the leaking dye is not visible to the naked eye.
Black lights are very cheap and available at big box hardware stores.
There are also black light bulbs that plug into standard fixtures, but I prefer a handheld flashlight that fits into tight spaces.
Remember, a black will not work without dye in the air conditioning system.
Use a sniffer
While all of the methods mentioned above work well to find a refrigerant leak, the preferred method for professionals is a freon sniffer.
This small device requires no additives and can quickly detect leaking refrigerant. While they are a bit pricey for a DIY’er, they are a vital tool for a professional mechanic.
A sniffer works by making an audible tone when it detects refrigerant. The tone gets faster as the device gets closer to the leak.
It is the ideal tool for finding leaks in areas that are hard to visibly inspect.
Related article: Learn how to flush your car AC
Fixing car AC once a leak has been detected
After the investigative work is over, it’s time to learn how to fix AC leak in car.
The leak must be fixed before recharging the system.
The location will dictate how the leak must be repaired, but it typically involves replacing parts.
Here are a few common causes of Car AC leaks and how to fix them.
Compressor
The engine spins an AC compressor on a vehicle and pressurizes the refrigerant.
Because of its moving parts, it is more likely to lock up or break internally than it is to lose refrigerant.
Nonetheless, if a car loses freon from the compressor, it must be replaced entirely.
The difficulty of the job varies dramatically between makes and models.
In some vehicles, the compressor sits on top of the engine, making for a quick replacement.
However, most modern engines have an AC compressor at the bottom of the engine.
Swapping a compressor involves unbolting it, disconnecting the signal wire, and removing the hoses.
ACLAB note:
Fixing or replacing some of the components can be quite difficult as a DIY job. Hence it is best to ask for professional help if you are in the slightest doubt or do not posses the necessary skills or tools.
AC condenser
The next repair is a damaged car AC condenser. This part is located in the engine bay and often bolted to the radiator.
It is very time-consuming to replace an AC condenser because the coolant has to come out of the radiator, and the fan, hoses, and wiring must also be removed.
Unfortunately, there is no shortcut, as stop leak treatments do not work, so the entire coil must be replaced.
AC condensers can also get pretty expensive, depending on the vehicle.
AC evaporator coil
Much like replacing an AC condenser, a leaking air conditioner evaporator coil is one of the worst things on a vehicle to fix.
An older truck tends to have the easiest access to air conditioner evaporator coils, which are commonly located in the engine bay.
However, modern cars are a nightmare since they have an evaporator coil located under the dashboard.
Removing the dash can take hours by itself and require specialized tools. The newer the car, the worse it gets, thanks to miles of wiring embedded in the dashboard.
Worst of all, many mechanics don’t want to fool with these replacements, and the cost for the owner will be in the thousands of dollars.
Replacing a car’s evaporator coil is not the easiest DIY repair, but it may be the only option.
Even professionals must look up a YouTube video or read instructions for these lengthy repairs.
Service ports
The high and low side service port is perhaps the best-case scenario. A leaking schrader valve often causes a leak under the plastic service port cap.
These are available at auto parts stores, along with the tool to remove them. Remember that a Schrader valve for an air conditioner differs from those used for tires.
Removing the Schrader valve without evacuating the air conditioning system will also vent any remaining refrigerant into the atmosphere, which is illegal.
Connections
The connections between air conditioner lines also provide a prime spot for leaks to start.
AC lines are aluminum, which can fatigue and break after years of movement. The rubber gasket inside each connection can also fail.
Fixing a connection consists of unbolting the hose and replacing the rubber seal.
I always try to get an OEM replacement gasket, but sometimes, the best AC leak sealer is the one on hand, and universal rubber O rings can be a lifesaver.
Recharge the system
After repairing the air conditioning leak, there are a few steps to complete, including vacuuming the system. Pulling a vacuum removes any air and moisture from the lines.
This is a critical step because air and moisture will damage AC components and lead to inefficiency.
Doing so does require a set of manifold gauges and a vacuum pump. Several auto parts stores loan this equipment as part of their tool rental program.
After running the vacuum for about 20–30 minutes, I close the valves on the gauges and wait another 30 minutes to ensure the pressure doesn’t drop.
If it holds, then I know that the repair worked.
Once I’ve verified that the air conditioning leak is sealed, I proceed to refill the air conditioner refrigerant.
Using a gauge that shows temperatures is critical because ambient temperatures can dramatically impact refrigerant pressure readings.
After charging the system, I always check to make sure the car blows cold air.
Signs of a car AC leak
What can cause the car AC to leak?
Natural wear and tear:
People are keeping their vehicles longer than ever, and this extra wear and tear means an AC system is bound to have problems.
The rubber seals rot and break down naturally over time. Similarly, aluminum hoses can fatigue and crack.
Unfortunately, there isn’t much preventive maintenance that could prevent these failures.
Damage from road debris:
Potholes and debris on the road are pretty common, and they can wreak absolute havoc on a car.
This includes a car's AC system, as a large rock can easily puncture a hole in the condenser coil.
Additionally, air conditioner lines can hang up on road debris or potholes, requiring major repairs to the whole system.
Stuck schrader valve:
The Schrader valve holds in all of the car’s refrigerant, and its seal can fail. It is common for leaks at the Schrader valve to start after connecting a gauge.
The valve may not seat properly and lose small amounts of refrigerant over time.
Overcharged air conditioning system:
An AC system with too much refrigerant can cause a leak.
A car’s AC system already relies on high pressure, and adding too much refrigerant can actually cause seals and hoses to fail.
FAQs
How much does it cost to fix an AC leak?
The cost to fix a leak can vary depending on where it is and what is damaged. Bad O rings or Schrader valves may cost a couple of hundred dollars to repair, while coil replacement could go into the thousands.
Can an AC unit on a car have a leak but still hold pressure?
Yes, most leaks are actually very small and develop into large ones over time. While some people choose not to fix slow leaks, I always recommend making the repair rather than putting refrigerant in a leaking system, as the problem will progressively worsen.
Is it normal for car AC to leak water?
Yes, leaking water is completely normal and does not require repair. Water dripping from the bottom is a byproduct of the air conditioner removing humidity from the car’s interior.
Can a car lose Freon without a leak?
No, the AC system in a car is a closed system, which means it should never need more refrigerant unless leaks exist. This is different from engine oil, which can burn off with use.
