When you need to flush and refill your AC system, you’ll probably be tempted to take your car to a shop. This will cost a few hundred dollars, so why not do it on your own? Like most car maintenance, you can DIY this project, as long as you have the right tools and guidance.
Start by disconnecting your AC system and flushing out all the tubes, condenser, and evaporator. Reconnect everything, checking for damages along the way. Refill your line through the low-side pressure port until you have enough refrigerant in your system and test the AC to see if it blows cold air.
This ultimate guide is all about emptying (and refilling) your car’s AC system. I put together in-depth step-by-step instructions that will guide you through the process. Let’s get started.
How an AC System Works
The AC system in your car works just like the one in your house. Air is passed over coils filled with refrigerant. The refrigerant changes the temperature of the air as it continues to travel. In your car, the air will eventually come out of your vents.
Within the AC system, refrigerant gets cycled and pumped through repeatedly. It goes through a series of compression, evaporation, and condensation cycles. The loop is completely closed, which means that you’re not adding new refrigerant, it’s just getting re-used.
The loop is pressurized and routed via changing pressure and a pump.
The second that your system gets open to atmospheric pressure or outside air, it can get contaminated and won’t work well anymore.
Defining an AC Flush
Once your system is compromised and there’s a contamination in your refrigerant, the only way to fix it is to replace all the fluid. This is done by “flushing” and then replenishing your refrigerant.
An AC flush is when you completely remove all of the fluid from your system. Since there are a series of looping and twisting lines, it’s not as easy as just opening a valve (like changing your oil).
Instead, you need to go through with a solvent and pressurized air. Doing this long enough will force all of the fluid and debris out of your system.
How Often You Should Empty a Car AC System
There’s no real need to empty your AC system as long as it’s working correctly. It’s not like an oil change where you need to swap out fluid every year or a certain amount of miles.
Rather, your AC system should only be emptied after one of three things happens:
Your compressor fails. This is easily the most common reason why someone would need to refill the AC system in their vehicle. When the compressor fails, debris and contaminants will be thrown into the refrigerant. In addition, the loss of pressure means that your system won’t work anymore.
Your system has been exposed to the outside air. Once a line is cracked, opened, or removed, then your system needs to be maintained. This entails dumping the current refrigerant and fully replacing it. Getting air in your lines will destroy your system and make it impossible to reliably generate cold air through your vents.
Your refrigerant has sat idle for a long time. If you’re working on a project car, there’s a good chance the refrigerant has sat idle in your car’s AC system for too long. It only circulates when the car is running and the AC is turned on. For project cars, you’ll need to flush and refill your refrigerant before hitting the road for the first time.
It’s a Lot Easier for a Mechanic to Help
I’m a huge fan of DIYing projects, but I need to be honest: it’s going to be a lot easier to have a mechanic help. Any given shop might do 5 AC flushes a day, and it’s no big deal for them. The key is that they have expensive equipment and expertise that allows them to blow through each project.
As a DIYer, it’s a lot harder to do this project. It’s definitely still possible, but just understand that it might be better to have a mechanic help, you’ll just have to pay a lot more.
What’s Required for this DIY Job?
- A socket set, screwdriver, flashlight, and pliers. In any of these DIY projects, it’s always a good idea to have some general tools on-hand. Since each car is a little different, I can’t guarantee which tools you’ll need, but all of them can come in handy.
- Gloves and safety glasses. Safety glasses are very important. You’ll be dealing with refrigerant and compressed air — a combination that can do serious damage to your eyes. Gloves will prevent you from inadvertently touching hot metals on your car.
- A gauge set. Gauges are used to refill your lines after the fact. I’m guessing you’ll need to do this, so I’ll include this in the process. The gauges read the pressure of your fluid lines.
- Pancake air compressor. The compressor will work to push flushing solvent through your system. Without the compressor, there’s simply no way to empty your AC system.
- Flush gun. A flush gun is imperative. I’ll talk more about it later, but make sure you have this before going any further.
- Flushing solvent. Flushing solvent gets loaded into the flush gun and is sprayed through AC components.
- A bucket. The bucket is used as an outlet to catch the debris and fluid you blow out of the line. A typical bucket is fine, you don’t need anything special.
- Spare 3/4 rubber hose. A hose will be connected to the outlet port and fed into the bucket. Again, you don’t need anything special, just as long as it fits over the outlet without falling off.
- Optional: Recovery machine. A recovery machine is what professionals use to empty a car AC system. If you can get your hands on one, this whole project will be expedited. If not, you can take the longer approach and still finish this job.
- Optional: Pressurized refrigerant can. If you’re looking to fill your car after emptying it, then you’ll need pressurized refrigerant. The amount and type you need will vary based on your car’s year, make, and model. Take a look at your owner’s manual to understand what you need.
Note for People Using a Recovery Machine
I’m going to assume that most people don’t have access to a recovery machine. These cost hundreds or thousands of dollars, and they’re very infrequently used for DIYers.
If you are using a recovery machine, you can skip most of the following steps. Instead of cleaning out the lines part by part, you’ll just hook the machine into the high and low fittings and let the machine do all the work.
To keep things easy, the “LOW” side is from the evaporator to the compressor (from the rear to the center of your engine bay). The “HIGH” side is from the condenser to the evaporator (from the front to the rear of your engine bay).
A recovery machine usually labels the ports, so you’ll just need to hook them into the appropriate fittings. The machine will run for a few minutes then you’ll need to inspect the levels.
If you’re using a recovery machine, I would highly suggest reading through the manual first. It will give you a thorough guide as to how to use it.
How to Empty a Car AC System in 15 Steps
Follow these steps to fully empty your car’s AC system. Make sure you read the steps before getting started, so you know what to expect. I’ll explain how to prep, flush, and refill your car AC system in the following 15 steps.
Step 1: Gather Your Tools
You should start by gathering all the tools you need for this project. It’s important to emphasize that you can’t successfully empty a car’s AC system with just compressed air, you need a “flush gun” as well.
If you don’t use a “flush gun,” you’ll just be wasting your time. The gun uses compressed air and a flushing solvent to completely remove the refrigerant from the line.
Without it, the refrigerant will still be present in your car’s AC system. The second the AC fires back up, debris will go back into the compressor, and you’ll need to redo this project.
This is also a good time to check your pancake compressor and see if it works. Make sure you have the right attachments to connect the flush gun to your compressor.
Step 2: Find the Right Place to Work
For this project, you’ll need to be on a perfectly flat surface. It might take a full day too, so make sure you can park and work uninterrupted.
It would be best to do this project in a garage that’s wide enough to move around and work. You don’t need to jack your car up (if that makes picking a spot easier).
Step 3: Park and Idle
Park your car in the spot, and turn on the parking brake. You’ll get the best results if you keep your car idling because that will keep fluid flowing.
However, you shouldn’t do this project right after going for a drive. You’ll be working in your engine bay, and you don’t want metal parts to be scorching hot.
It’s possible to do this with your car turned off. The only problem is that the refrigerant will be stagnant and might be hiding within a loop somewhere in the system. If you don’t want to idle, you need to make sure you turn on your car after blowing out the lines in order to see if anything recirculates.
You’ll wind up redoing a lot of steps if this is the case.
As you’re working, be mindful of moving parts and hot metal. You’ll likely be leaning over your serpentine belt which will be spinning rapidly, so don’t wear any loose clothing or jewelry, and tie up your hair.
Step 4: Find the Parts
This part can get a little annoying. You’ll need to locate at least 3 parts within your AC system that you’ll flush: your evaporator, condenser, and liquid line.
Since this will vary from car to car, it’s not as simple for me to tell you where they are.
I can say, the evaporator is probably towards the back of the engine bay, near the sheet metal of your vehicle (right behind the dashboard). It has metallic fins running up and down with two ports, an inlet, and an outlet.
The condenser is towards the front, near your radiator. It also has fin-like tubes running across the part with an inlet and outlet port.
The liquid line is a piece of metal, not rubber. It runs between the condenser and evaporator.
For this process, you won’t need to remove or replace the evaporator or condenser. However, there are some people who are reading this guide because they’re replacing a compressor, which is a separate part from these 3.
Step 5: Identify and Prep the Fittings
Once you find the parts, you’ll want to locate the fittings. Each part has an inlet and outlet port, and it’s important to understand which is which.
Blowing air in the incorrect way can do damage to your vehicle or not flush it at all.
To prepare the fittings, you’ll need to remove any connections in the outlet.
Step 6: Attach a Hose to the Outlet of the Evaporator
Let’s start with the evaporator. Remember, this is the part at the rear of the engine bay.
The outlet will run to the compressor, and that’s the port you should care about. Remove the connection to expose a metal piece of threaded pipe, which is the outlet.
Use your 3/4 rubber hose and push it so it hugs this outlet. If the hose is oversized, you’ll need to keep a hand on it as you work through this step. If it comes loose, the refrigerant will dump into your engine bay and will make a mess in your garage.
Step 7: Place Other End of Hose in Empty Bucket
The other end of the same rubber hose needs to be positioned into an empty bucket. This is where all the refrigerant and debris will be blown into.
Using a 2-gallon bucket from Lowe’s is perfect, but you can go bigger if you want to.
To make things easier, place the bucket on the ground and put the hose in it. Since it’s downhill from the port, this process won’t dump refrigerant back up the hose when you’re done spraying.
Step 8: Wait a Few Minutes
After doing this, it might take a few minutes for the pressure to equalize within your AC system. After all, you just exposed the system to atmospheric pressure.
Step 9: Blow the Evaporator’s Inlet with the Flush Gun
Next, expose the inlet of the evaporator. This is the remaining of the two outlets, and it’s the one you haven’t touched yet. The inlet is where refrigerant goes before cycling through the evaporator and going to the compressor.
The inlet port will likely look just like the outlet. In this step, you’re not putting a rubber hose around the inlet — instead, you’re placing the nozzle of the flush gun in the interior hole of the inlet port.
Before doing that, make sure you have enough flushing solvent in the flush gun. You don’t need a ton to get great results, so try to underfill rather than overfill the reservoir.
With everything set up, turn on your pancake compressor and hold down the trigger on the flush gun.
You’ll want to flush for about a minute or so.
In the first few seconds, you’ll notice the most fluid and contaminants pour into the bucket you set up. After that, the results will be slower, but it’s important not to stop prematurely.
Contaminants can be hiding in different corners of the evaporator, and stopping earlier will allow these contaminants to just recirculate after you’re done.
Once you’re satisfied with the flush, remove the flush gun and the hose from the outlet. Keep the fittings removed, because you’ll clean them too in a few steps.
Step 10: Repeat the Process for the Condenser
With the evaporator done, you’re ready to move to the condenser. This will be at the front of the engine bay, closest to the grille of your car.
The outlet is the lower of the two ports, which makes it easier to pinpoint it. You’ll want to remove the connections from the inlet and outlet port in order to repeat the process.
With these ports exposed, you’ll use the same hose and connect it to the outlet, running the other end into the same bucket.
Position yourself so you can see and easily access the inlet. Top off the flush solvent if you need to, and grab your flush gun. Turn on the pancake compressor and make sure the connection is snug between it and the flush gun.
Put the nozzle of the flush gun in the inlet, and hold the trigger for a few minutes.
Now, your condenser is flushed and empty. There’s no need to replace the fittings yet since you’ll be cleaning those in a second.
Step 11: Remove and Drain the Liquid Line
There’s a liquid line that refrigerant will travel through in your AC system. A lot of cars have a loop or some sort of bend within this line. That makes it difficult to successfully blow out the line without using professional equipment.
For that reason, I would suggest removing the liquid line. It should just have a threaded pipe fitting on either end, so it’s easy enough to remove with an adjustable wrench.
You don’t have to replace this line, you can put the same one back on after draining it. To identify it, it’s a metal line as opposed to rubber lines that run everywhere else. It’s usually found near the battery.
Take a second to inspect the line. If the insulation is torn in any areas or you notice pits from corrosion, you’ll need to swap out this liquid line. If everything looks good, then clean the line before reinstalling it on your car.
To clean it, just put the line in a bucket upright. Use your flush gun on one end and run it for about 30 seconds to fully clean the line. Reinstall it where you found it.
Step 12: Drain Each Removed Hose
Every hose within your AC system has a chance of having refrigerant in it. Before reattaching your evaporator and condenser, you’ll have to drain each of these hoses.
The process is the exact same as step 11. You’ll hold the hose upright in a bucket and use your flush gun in the open end. Each hose should get treated for about 30 seconds to fully flush them.
It’s important that you remember where each hose came from. They’re likely different lengths, so they’ll only get attached a certain way.
If you have an additional hose near your compressor, you should also remove it and clean it at this time. You haven’t touched the compressor at all, so you’ll have to find it and remove additional hoses.
If any of the hoses or fittings are cracked or damaged, you’ll need to replace them before reinstalling the system. An AC leak will cause your HVAC to stop pumping out hot or cold air.
Step 13: Reinstall Everything
By this step, you’ll have a number of clean, but disassembled parts. You’ll have to go through and reinstall everything that you took apart.
It’s easiest to start with the AC hoses and fluid line. Make sure they’re pushed snugly onto every port. If they’re even a little loose, the pressurization can blow them out and cause a leak.
Triple-check everything to ensure you didn’t forget a hose somewhere.
When this step is done, your AC system should be fully assembled, and it should be ready to get filled.
Step 14: Fill the Low-Side Port
The new refrigerant needs to be added to the low-side port. As a reminder, this port is labeled “L” and it appears between the evaporator and compressor.
Unscrew the “L” cap and fill up the port.
Be extremely careful as you use and handle this refrigerant. It’s incredibly cold and can frostbite your skin and lead to serious injuries if you come in contact with it. Never take off your safety goggles as long as the can is in your hand, and use safety gloves and long sleeves to handle it.
Start your car and let it idle. Turn the temperature setting to the coldest AC setting in order to activate your compressor. Hold down the nozzle of the refrigerant can.
The built-in gauge will tell you the pressure and how filled the system is. You might have to go through two cans to completely fill your system.
Step 15: Finish Up with the Gauge Set
Now it’s time to grab your gauge set. This has three lines, two gauges, and a number of valves. The blue side hooks into the low-side port, and the red line hooks into the high-side port. It’s very important that you connect it correctly, or it will undo all your work.
Since you’re refilling refrigerant, you’ll want to close the red half of the gauge set. You’re not adding anything to the “high side.”
In the center, there will be a yellow line. Remove the one end and screw in your can of refrigerant. You need to make sure that the can has the correct top that can be attached to this set.
Next, take the blue quick-connect valve and connect it to the low-side port. Tighten the valve fully by spinning it clockwise hand tight. Open the blue valve on your gauge set to allow the refrigerant to start traveling.
Wait until the gauge tells you that the refrigerant pressure is acceptable. Congratulations, you just emptied and refilled your car AC system.
At this point, you know everything you need to know about your car’s AC system and how to empty it. The process can be tedious and take a long time, but it’s definitely possible to do it on your own.
For more car DIY guides, check out my blog. Leave a comment below if this guide helped you and let me know what else you’d like to see on my site. As always, be sure to check out my ultimate list of recommended car products.