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!


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.

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  • Thanks! I have 2 ton 4.1lbs R22. How much do I need? Thanks! – Carrie Jun 11 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 at 15:12

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