It looks like I lost all of the refrigerant due to a leaky schrader valve and O-ring. The A/C stopped cooling a few months ago, but I just got around to tracking down the problem.

Do I need to flush the system, replace the compressor oil, etc? Or can I just replace the leaky valve and o-ring and re-charge the system?

Some of the suggestions I've seen say to add 1-2 oz of compressor oil even if none has come out. Can the compressor oil be over filled?

  • 1
    In general you need to draw a vacuum on the system and leave the vacuum in place for at least an hour. Check your system to see the exact amount of refrigerant needed and only use that amount (use a scale which can measure it to the 1/10th oz at least). If the system keeps the vacuum, then add the refrigerant. Use refrigerant with added stop leak and compressor oil. This is my opinion of what to do, as I'm not an A/C expert. I'm sure there are some better suited to post with a more qualified answer. Jul 29, 2015 at 16:31
  • 1
    Also, depending on the vehicle manufacture (year/make/model), you'll need to know whether you need to replace the dryer as well. In some cars, when these are subject to atmosphere, they will need to be replaced as well. Jul 29, 2015 at 16:32
  • Thanks all. This project has been on hold since I posted. Hopefully i'll get to it next weekend.
    – RayInNoIL
    Aug 27, 2015 at 18:42
  • 1
    @Paulster2 Best to not used the stop leak. It works poorly, can decrease system performance and, of major concern to me, it can ruin a multi thousand dollar A/C machine. Dec 28, 2015 at 6:19
  • 1
    @FredWilson - Which is why I left it as a comment. :-) Dec 28, 2015 at 12:52

1 Answer 1


Air in an A/C system is a significant contaminate. It raises pressures and decreases cooling efficiency.

System refill steps:

  1. Pull vacuum on the system to 29mm/hg for at least 1/2 hour. This low pressure and time has two purposes.

    • Removes almost all the air.

    • boils out any water that may be in the system.

  2. As a leak check; seal the system with a gauge attached for at least 5 minutes. The pressure should not drop. If no leaks...

  3. Charge with the precise weight and type of refrigerant specified.

Oil can be overfilled. Doing so will decrease cooling efficiency. Adding with no loss evident can result in overfilling. Low oil amount will cause compressor damage.

Flushing is a challenging project and only required if the system is contaminated. If the system has been open to air. The receiver/Drier need be replaced. It has a desiccant that absorbs water.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .