When an air conditioning system loses its ability to cool properly, it may be necessary to recharge the system. Below covers how to recharge the A/C system when the system is low on pressure or has been vacuumed out following a repair.
Note: Always wear safety glasses and gloves when charging the A/C system.

1. Determine ambient air temperature.

If the temperature of the air is 55° or below, do not charge the vehicle. It is recommended to use a charging hose with a gauge. The refrigerant packaging should contain a chart for determining what pressure to charge the system depending on the ambient air temperature. (If no chart is provided, use the chart in this guide). Following the chart when recharging the system will ensure that the system will operate efficiently.

2. Locate the low-side service port.

This port is typically found on the line connecting the accumulator and compressor. The high side fitting is located between the compressor and condenser. Consult the service manual to verify the exact location of the low-side service port.

*Most 1994 and older vehicles used R12 as the original refrigerant, if the vehicle being serviced is still using R12, it must be evacuated and retrofitted. Mixing R12 and any other refrigerant is illegal. Never use the high-side port to add refrigerant, doing so is very dangerous and could cause harm.

3. Wipe away any dust with a clean rag and then remove the cap from low-side service port.

4. Attach the charging hose to the low-side service port and ensure that you have a secure connection.

If the hose does not attach easily you may be using the wrong port.

5. Following the instructions on the refrigerant package, add refrigerant to the system.

6. After determining the correct pressures using the ambient air pressure chart, monitor the pressure readings constantly while charging the system.

7. After the air conditioning system is charged to the proper pressure, remove the charging hose from the low-side service port leaving the can attached to the charge hose and store any additional refrigerant in a dry cool spot.

8. Check the service port cap seal before reinstalling.

Ensure that the seal beneath the cap does not have any cracks, nicks, or tears. This seal can be added protection if the Schrader valve ever formed a leak.


  1. It is best to purchase the Haynes manual – Automotive Heating & Air Conditioning for use while performing the job.

  2. Have any refrigerant still in the system recovered by a certified A/C Technician.

  3. Disassemble the system by removing all the components including the hoses.

  4. Flush components that will be reused. Use an A/C Flush Kit and solvent. The instructions for properly flushing the system are included with the kit.

    • Condensers that have a parallel tube system cannot be properly flushed and should be replaced.

    • When flushing any component pay attention to the flow of solvent and air exiting the component. If the flow is restricted there may be an obstruction, try reversing the flow and if unsuccessful, replace the part.

  5. Replace o-rings and Schrader valves on components being reused.

  6. Reassemble the system. The instructions or notices with the new compressor should inform you if the compressor already contains oil. If not, consult the Haynes: A/C manual for proper type, weight, quantity, and procedure for adding oil.

    • *A good practice would be to add a UV dye to help with diagnosing any potential leaks in the future, as well as aid in lubrication.

    • **Install the accumulator or receiver-drier last. Do not remove the plugs on this component until immediately ready for installation, the desiccant bag within will begin absorbing moisture immediately.

  7. Double check that all fittings, mounts, and electrical connections are secure.

  8. Attach manifold gauges and vacuum pump and apply 29 in/Hg of vacuum for 45-60 minutes to remove all moisture and air from the system.

    • * After applying vacuum, switch the vacuum pump off and let the system sit under vacuum for 30 minutes and check vacuum gauge to ensure there are no leaks.

  9. Consult the A/C repair manual for required quantity of refrigerant or ask the experts at Costa Oil -10 Minute Oil Change. Start vehicle and turn the air conditioning on the coldest settings and blower fans on high then introduce refrigerant into the system. Consult the manual for proper low-side and high-side pressures. It is important to follow the instructions that account for outside air temperatures and altitude etc. Filling to the specific pressure and quantity are very important for efficient and safe operation of your air conditioning system. See the chart above for reference.