How to recharge car air conditioning and find leaks

R-134a rechargeAfter purchasing a used 1998 Saturn SL2, I needed to recharge the air conditioning system with R134a refrigerant because the A/C would only blow warm air. This blog post describes how to recharge your vehicle’s air conditioner, and the instructions here are general enough that they will apply to practically all vehicle makes and models. If you find yourself needing to replace your A/C system’s valve core (Schrader valve), then see my other blog post describing how to do that:

Note: if your vehicle is older than approximately 1994, then it may require R-12 refrigerant instead of R-134a, and will either need to be serviced by a mechanic or retrofitted with R-134a connections. Do some internet searches to find out more about that.

WARNING! Be careful not to get any loose clothing, hair, or any part of you near the hot or moving parts in the engine bay of your vehicle. Serious injury (or worse!) can happen if you do.

Materials Needed

Goggles, gloves, R-134aYou only need the following items to recharge your A/C:

You can usually get the cans of refrigerant with a dispenser all included in a kit. If you already have a dispenser then all you need is the R-134a refrigerant.

Should I Use Dye and Stop-Leak?

There are a lot of discussions out there about what R-134a refrigerant you should use. I would recommend that you use one that has dye in it so that you can find any leaks that may be present in your system. However, an even bigger concern people have is whether or not they should use refrigerant that has “stop-leak” in it. At first it looks like an attractive option since it could stop your system from leaking. However, people worry that whatever is in there that is stopping the leaks will also clog up their A/C system.

As far as I can tell, there are two types of stop-leak formulas, and for some reason the company Interdynamics seems to be the leading manufacturer most types of refrigerant. According to their website, one of the stop-leak formulas is safe for your system, as it only reconditions the rubber seals in the system and makes them swell (so hopefully that’s where your leak is). The other non-system-safe formula will put all sorts of gunk in your system and will probably ruin your A/C system over time – that formula is meant for leaks that occur at places other than rubber seals and will make it so no repair shop will ever touch your A/C system again. Here is some of the info directly from their FAQ page:

"Are leak sealers safe for my A/C system? What does ‘System Safe’ leak sealer mean?
Yes. IDQ ‘System Safe’ leak sealer is a gentle o-ring conditioner that does not destroy o-rings."

"How will IDQ leak sealer affect my O-rings over time?
IDQ ‘System Safe’ leak sealer will rejuvenate and condition your o-rings. There is no deterioration over time."

"Which leak sealer product should I use — Stop Leak & Detector, A/C Leak Sealer, or one of the refrigerants containing leak sealer additives?
Stop Leak & Detector (LDS-1) has both leak sealer (for rubber components) and red dye to help you spot the location of any larger leaks that are too big to seal and require replacement.
Super Seal (#323 & MRL-3) seals leaks in both rubber and metal components. It is recommended as a potential fix for older vehicles that are not candidates for mechanical repair."

I decided to use their Arctic Freeze Kit AFK-11CS product, as it contains both dye and the "safe" stop-leak stuff in the refrigerant and includes a dispenser with inline pressure gauge. I got it on eBay for $35.

What is Wrong with My A/C?!

There are several things that can cause your air conditioner to stop working and only blow warm or hot air. I’m not an expert in this area, but I can at least give a few pointers that I found interspersed on the web that can help you quickly decide if a simple A/C recharge will be sufficient for you.

  1. Lift the hood.
  2. Start the car.
  3. Turn the air conditioner on full blast (all the way to the “cold” side and with the fan on the highest setting).
  4. Look at the A/C compressor (see picture below for a general idea of what this looks like).

Compressor with pulley
The A/C compressor. The pulley will always spin when the car is running. The center portion inside the pulley will spin when the A/C is running, otherwise it will be stationary. Click image to enlarge.

Is the inner portion of the compressor spinning along with the pulley (i.e., the clutch is engaged), or is only the pulley spinning, and the inside portion is not?

If it is all spinning, then you probably only have a leak somewhere and otherwise have a functional A/C system.

If the A/C clutch is not engaged, then you might have bigger problems. To get a better idea, you should but some refrigerant into the system first – this sometimes lubricates the compressor enough to allow the clutch to engage properly again. This is explained more in the procedure below.

Locating the A/C Low-side Port

Your air conditioning system has a low-side port and a high-side port (see picture below). Both are pressurized, but the low-side port is under much lower pressure than the high-side port. The low-side port has the smaller connector (but is connected to the piping that has has the larger diameter). The high-side port is the other one – the larger connector with the smaller-diameter piping. When recharging your air conditioning, only connect the refrigerant can to the LOW-SIDE port! If you search the web for recharging your A/C, most sites tell you that the can of refrigerant will explode if you connect it to the high-pressure side.

Low- and high-side AC ports
The low-side and high-side ports connecting to the A/C compressor. Recharge on the low-side (low side refers to internal pressure, not to physical location). Click image to enlarge.

Recharging the A/C System

To avoid potential injury, make sure to wear safety glasses and gloves while doing the recharge. Once you are wearing these, you can continue with the steps below. It is fairly straightforward and you can just follow the instructions that come with your dispenser and refrigerant. This is the general method to recharge your A/C:

  1. Lift the hood.
  2. Start the car.
  3. Turn on the air conditioner. Turn it to full blast (all the way to the “cold” side and with the fan on the highest setting).
  4. Removing the low-side capUnscrew the low-side port’s cap. There is a valve inside that keeps the pressure from being released. The cap is just to protect the valve and creates another seal. Note that sometimes the valve (also called a “valve core” or a “Schrader valve”) might be faulty and leak, but you probably won’t be able to tell until after you have recharged the system.
  5. Attaching can to dispenserAttach dispenser and refrigerant. Screw the dispenser hose onto the can of refrigerant. Read the instructions that come with it – some of them you only have to tightly screw them on, while other sometime require to be screwed on tightly and then backing out the puncture tool a bit.
  6. Make sure that your air conditioner is turned on!
  7. Attaching to low-side portAttach dispenser to low-side port. The loose end of the hose has a shroud around it that you pull back to be able to connect it to the A/C system’s low-side port. Pull back the shroud, connect the hose to the low-side port, and the release the shroud. That end of the hose should now be securely connected to the low-side port. Give it a little tug to make sure it is secure.
  8. Inline pressure gaugeRead pressure gauge. If your dispenser comes with an inline pressure gauge, then you should now be able to see the pressure on the low-side port. If it doesn’t show the pressure, then your system either has no pressure, or the connector isn’t fully seated to the low-side port. On my car, I had to keep my hand on the hose/low-side port assembly to maintain a good connection.
  9. Adjust gauge’s temperature dial (if applicable). My dispenser’s gauge had a dial that turns so that I can specify the outside temperature, which in turn indicates what the "proper" A/C low-side pressure is supposed to be.
  10. Compressor with pulleyCheck compressor’s clutch. The A/C clutch should be engaged, so that the inner portion is spinning with the pulley. If it doesn’t ever start spinning then you may have to get some refrigerant into the system before it will start spinning. If it still never starts spinning even after you have put some refrigerant back in, then you have other problems with your compressor and should not continue with this recharge procedure.
  11. Filling with R-134aPress the dispenser’s trigger (or whatever means you dispenser uses to release the refrigerant from the can). This should be done with the A/C compressor spinning.
  12. Rotate the can between the 12:00 position and 3:00 position while filling the system (per the manufacturer’s instructions).
  13. Keep checking the gauge. When are filling the system, the inline pressure gauge (if you have one) will read zero because the A/C pressure is the same as the pressure in the hose. Release the dispenser’s trigger (or what-have-you) to stop filling the system every 10 seconds or so you can get a valid pressure reading from the gauge.
  14. The system is recharged when gauge shows that the pressure is in the "proper" range.
  15. Released the dispenser trigger (or what-have-you).
  16. Remove the dispenser hose from the low-side port.
  17. Place the protective cap back on the low-side port.
  18. Let the car run for several minutes. The air vents inside the car should now be blowing cold air.

Checking for Leaks

If you used the refrigerant that has dye in it, then you can check for leaks in you system after letting it run and/or driving it for several minutes.

On my vehicle it was obvious that the valve core (Schrader valve) was the culprit, because after I removed the dispenser hose, the valve was bubbling quite a bit of the bright green dye and letting out the refrigerant that I had just put in (see picture below). If you are having the same problem, then go see my other post that explains how to replace the valve core (and how to do so without discharging the A/C system’s refrigerant & pressure) at

The leaking valve core
Leaky valve core leaking and bubbling up the fluorescent green dye. No good! Click image to enlarge.

Use a black light (i.e., ultra-violet light source) and shine it around your engine bay – focusing on the A/C compressor and following it tubing to the condenser and any other components connected to it. You should be able to make a full loop – starting at the compressor, following one pipe to the condenser, and then the other pipe back to the compressor. If there are any leaks, the some dye will have escaped there and the UV light will make the dye glow very brightly. This may work better for you at dusk or in a dimly-lit garage. You should also check again after a few days of use to help find any smaller leaks.

After you have found any leaks, you will need to repair or replace the components that are leaking. This is usually a job for a mechanic unless it is some small, easily accessible component. Just the knowledge of the problem is the important part, though, as it can give you a good indication of how much the repair will cost. It could be a few dollars for a Schrader valve, or closer to a thousand bucks for larger problems!

Cool Off

Hopefully you don’t have any leaks and can now take a few minutes to enjoy a nice, cool car again!

7 thoughts on “How to recharge car air conditioning and find leaks”

  1. I have to agree on being careful about which stop leak product you want to use if you go down that road. Fortunately there’s a ton of information online available for you to dig through before you make a purchase. Buying something that gunks up your system can lead to bigger problems. I’ve had success with Red Angel A/C Stop Leak ( and I used it specifically because it doesn’t contain any particulate matter. Do your homework!

  2. Recharging an A/C system the way described here is pretty unsafe. You should never do anything on an A/C without having plugged a proper set of pressure gauges to monitor the pressure or both the low *and* high pressure sides. By not doing so, you’re going completely blind while recharging and you might be blowing up expensive parts of the system without even knowing. Also when a system is completely empty you’re supposed to plug a vacuum pump on it to empty it from any residual moisture. Again, not doing so will eventually result in some potentially expensive components failing prematurely. This also allows to quickly check for leaks (thus potentially sparing you to waste an entire can of refrigerant that will end up outside almost immediately) by checking that the depression stays after the pump is turn off.

  3. Really helpful. The information about looking to see if the center portion inside the pulley is spinning on the compressor unit helped me determine that the wire going to the switch to turn the compressor on was rubbing on the belt which caused a short. This blew the 10 amp ac fuse located in the right side fuse box under the hood. All I had to do was cut and crimp the wire and replace the 10 amp fuse. It works just like it always has. I am considering checking the temperature of the cold air at the vent to see if a recharge with new refrigerant is necessary. Thanks for the helpful information,

  4. Put a re-manufactured compressor on my car that they said they tested, it turns on and the clutch activates fine but won’t hold a charge. When recharged by a pro the temp didn’t change hardly at all. Going to use this method. Thanks.

    We offer the best Air Conditioning in Adelaide

  5. I put 2 cans of Freon in my 94 Toyota Camry sometimes my a/c cools and then starts to get warm. Do I need another can.

    1. 2 cans should be more than enough. Perhaps you have a leak somewhere? You should get an A/C pressure gauge and check that it’s in the right pressure range before adding any more cans. Some A/C recharge kits come with the gauge (like in my post).

  6. Hi Mike,

    Can you respond to Bruno’s comments above? I’ve seen posts and videos making an AC refresh seem like no big deal as long as instructions are followed, then others like Bruno talk about blowing everything up, lol.

    Are there reasonable concerns when this is done without the expensive extra steps taken by pro service shops?

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