Recharge the Air Conditioner in a Car

Do-it-to-yourself auto air conditioning recharging requires eye protection, a charging kit, refrigerant, and some practical knowledge. Keep in mind, if you do not have the manufacturer's specifications and a charging manifold with gauges, you will not be able to do a professional job, but many people successfully recharge their AC with kits available at big box stores and auto parts retailers. Try to get a kit that includes a pressure gauge, this will make troubleshooting and charging easier. Be aware that this particular process is usually best left to a professional mechanic.


  1. Determine if you have any refrigerant left in your system at all. To do this, you will need to fit a charging hose on the low pressure port, which is on the refrigerant line on your car, usually near the accumulator. Be sure to use eye protection. If your system is completely discharged, it may be contaminated with moisture, and charging will not give satisfactory results unless the source of the leak is found, repaired, and the receiver dryer is replaced. The open system must be repaired and purged using a vacuum pump to remove air and moisture. You will also want to add compressor oil if the system has been leaking. Evidence of oil leakage and measurement of oil left in a replaced compressor will be a guide as to how much oil to replace.
  2. Check for any obvious leaks. If your system has lost sufficient refrigerant to quit working, you have a leak. Small leaks may take months to deplete the refrigerant so that the AC fails to cool, but charging a system with a significant leak is simply a waste of time. Look for refrigerant oil residue on hose, tubing, and fittings that are part of the refrigerant system. Spray a soapy water solution on fittings and watch for bubbles to appear, indicating a leak.
  3. Make sure the condensing coils are not obstructed with debris, and that the compressor is operating. To test a compressor with a low charge you may need to jump the pressure switch, often located on the accumulator.
  4. Tap your refrigerant can. This is done by completely opening the valve on the tapping fitting, which retracts the tapping pin into the valve body. Failing to do so will result in the tap puncturing the can when it is installed, releasing the refrigerant before the fitting is sealed.
  5. Securely thread the tapping valve on the refrigerant can, close the valve completely shut. This drives the pin into the top of the can, making it possible to release the refrigerant when the valve is opened.
  6. Purge the charging hose. Open the valve until you hear it fill with refrigerant, then slowly loosen the brass fitting that connects the hose to the valve. Be careful not to allow refrigerant to spray on bare skin, as this will freeze skin tissue on contact. Re-tighten the hose once you have heard refrigerant escaping; this should have forced any air (and moisture) from the hose.
  7. Locate the low pressure charging port on the refrigerant line on your car. This will be on the larger tube, usually near or on the accumulator. Connect the quick coupling and make sure it is not leaking.
  8. Crank your engine and turn the AC on high cool, high fan. If your recharging hose is equipped with a pressure gauge, check it to determine if the system needs refrigerant. If the pressure holds steady in the recommended range, the system is full and should not be charged. If the pressure is below the recommended range, follow the instructions to recharge the system.
    • Another indicator that the system needs refrigerant is that the compressor cycles rapidly. If the compressor switches on and off every 5 to 20 seconds, it is most likely due to low pressure. You will see the pressure drop when the compressor kicks on, the compressor will shut off when the pressure gets too low, and the pressure rises back up to the operating range as the system equalizes. Compressor cycling (switching on and off) in a completely charged system should be very slow (every 30 seconds or up) or not at all present (compressor stays on) in hot weather.
    • Be aware if the cooling fans for the radiator are on and functioning with while the AC system is on. If the compressor is on, the cooling fans should also be on to assist in cooling the freon in the condenser, located either in front or behind the radiator. Most vehicles have 2 fans, with one being dedicated to the AC system
  9. Open the valve until you hear refrigerant passing through the hose.
  10. Allow the can to dispense its contents. This often takes anywhere from two to five minutes. The hotter the outside temperature, the more quickly the contents will discharge. Keep the can with the tap up at all times, to allow non-liquid refrigerant into the suction side of the system to prevent compressor damage. Do Not overcharge! A manifold gauge should be used to measure both high and low side pressure. Consult a Pressure temperature chart.
  11. Close the valve and disconnect the hose when the can is empty or no longer discharging enough to keep the can cold. Check the charging port for leaks, and replace the plastic cap.
  12. Check the air from the AC vents in the car. It should be blowing cold (38-45 degrees), if not, either one can of refrigerant was not sufficient to charge the system, or some other component is the problem. Do Not overcharge! A manifold gauge should be used to measure both high and low side pressure. Consult a Pressure temperature chart.


  • Later vehicles run on R134a. These systems have different size ports, making identification easy.
  • Generally avoid a kit that contains a substance for sealing leaks. The sealant can harden in inappropriate places and cause problems; get the leak fixed properly, or, if it is a very slow leak, just leave it be.
  • If your car is earlier than approximately 1993, the air conditioning will operate on R12 which is now obsolete. However there are replacement refrigerants such as Freeze12 which will not require you to convert your system to R134a in order to recharge.
  • You can get an R12 to R134a conversion kit at an auto parts store, but should consider having it done professionally.
  • A DIY air conditioner recharge can be pretty risky. You can look at your manifold gauges for the Hi and Lo sides and determine if the system is low, but it won't tell you how low the system is. You need to be fairly accurate in the amount of freon you add in order to prevent damage and for the system to work. The only way to know how much freon is in the vehicle, is to remove it and weight it using an A/C servicing machine that recovers as well as charges. In most cases, it's best to take your car to a professional for this service.


  • R-12 is no longer used because it contains CFCs and is harmful to the environment if it gets out of the system.
  • R-12 is now more expensive and can be found on eBay. Although it requires a license to buy, and to evacuate and recover a system. Getting caught doing so without a license will result in a fine and/or imprisonment. So it may be wiser to have your A/C converted to R-134A. This can easily be done with the retrofit conversion kits on the market now. Some even come with how to videos.
  • Don't mix R-12 and R-134 refrigerant. This is not illegal, but isn't efficient. R12 and R134a require different oil for lubrication. R-12 systems use a mineral oil, R-134a systems use a polyalkylene glycol (PAG) oil. A mixture of the two will displace more space than needed in the system and could result in an overfill, stressing the compressor. If you change the compressor, it is highly recommended to also change the filter/dryer and you may have to flush the condenser. Either Ester or PAG oil can be use on a conversion.
  • One thing to consider with PAG oil is if it is left out it will absorb humidity and water. It also can become an acid and corrode your A/C system and cause leaks.
  • Get a recharging kit that includes a pressure gauge. Beware that once the low side reaches around 30 psi the high side can continue to increase to excessive pressure levels if not monitored — do not overcharge, fix leaks use a manifold gauge set and be safe!

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