My central AC is a 16-year old Trane one package unit on the roof top. However, it is not cooling very well. I brought contractors in and it seems that R22 freon is leaking. However, every contractor gave me a different number of freon that I need to fill.

My question is 1) is it possible to test freon level for a one-package unit? If so, how? 2) do I need to replace it? Trane has solid quality and I thought it can last longer than 16 years. Replacement for a roof top central AC is so expansive since we will probably need a crane.

Many thanks in advance!

1 Answer 1


16 years is good , it would be hard to give an exact # but based on the size and the age of the system even I could give an idea based on the size and it is still functional, 5 ton 10 lbs R22 simple top off at this age if a couple measurements prove the system is healthy and only needs a charge that may last 7 years , I base future at 1/2 if only low on charge bigger system more refrigerant smaller system less.

  • Thanks! I have 2 ton 4.1lbs R22. How much do I need? Thanks!
    – Carrie
    Jun 11, 2020 at 1:06
  • If it is cooling less than 3 lbs will probably bring your sub cooling and super heat numbers in spec.
    – Ed Beal
    Jun 11, 2020 at 15:12
  • Back in June, I had someone fill in R22 close to 2 lbs. After that, the AC can only bring temperature down to 76. Now after about 2 months, I find the cooling is not as well as it was in June. It looks the leaking is still happening? Correct me if I am wrong. So, I am thinking about having someone to change the coil and have a new one. Evacuate R22 and re-fill to full. Is it worth of doing that?
    – Carrie
    Aug 17, 2020 at 15:51
  • If you are changing a coil I would also replace the outside unit and update to a newer type of refrigerant unless you are absolutely sure the leak is in the coil. If you know the leak location it makes sense as the Freon can be recovered and reused. But if not sure at 16 years old I would say it’s a gamble because R22 is so expensive and only going to increase in cost until it is no longer available.
    – Ed Beal
    Aug 17, 2020 at 16:45

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