I have a 27-year old central A/C in my house. At the end of last summer, it stopped blowing cold air and after some investigation, my A/C company determined that there was a leak (maybe more than one) in the evaporator coil. They added 4 pounds of freon and put some sealant into the system. They also told me that given how old the unit was, it made no sense to try to fix it, and that most likely it would start leaking again soon.

Well, I've been getting estimates to have my a/c replaced all spring, and in the meantime, my old A/C has been working okay. I've already used it probably about 10 days this year. So now I'm wondering why should I replace an A/C that works, especially considering how expensive it is.

My question is, should I still expect it to stop blowing cold air any day? How well do those sealants work? Frankly, based on what they told me last year, I didn't expect my A/C to work this year at all. Will measuring the temperature at the vents will give me any indication of how close to the end my A/C is?

 

You can take temps at a supply duct and at the return duct. That will give you the temp drop across the coil. Should be between 15* - 20*.

 

Yes, that's what I've been doing. But my question is, if from day to day the difference stays the same, is that an indication that there is no leak? If there is a slow leak, would the temperature drop be getting smaller and smaller every day?

 

It could take weeks or even month's to see a change. If it was slightly over charged could take longer. I have had 50% success with sealant.

 

27 years old is about 14 past average. The $30 plus dollars a month in energy savings should help offset the price. Plus better comfort.

 

Most people that I've seen in your situation take a wait and see approach. From what you are saying it seems to be holding fine. If it gets worse you can always add some freon or choose to change the system at that time. I have many customers who are happy adding some freon every year or so, instead of paying thousands for a new unit. New units are especially lately are having many problems of their own.

 

Don't forget Murphy, if anything can fail, it will ,at the worst possible time.
Just Saying!
Geo

 

You need to plan on replacement if not now, in the not so distant future. It's better to have a plan and be able to pay for the replacement than get caught with your pants down.

 

Thanks everyone. Another concern is if the coil is slowly leaking freon, doesn't it just go into the air inside the house, which can't be good for those in the house?

 

Yes, the Freon will get into the house, but the leak should be very small and very slow, so no need to worry.