I own a Lennox Elite 10 purchased in 1996. In the last four years I have had four technicians out five different times to find a freon leak. They are unable to find the leak & the remedy has always been to put freon in. This year a different technician said he had a new product that should plug the leak when he put freon in. It worked for a month to six weeks & I again had no cold air. Now I find that it takes about forty minutes after I turn the AC on before I get cold air. I'm not sure if the compressor is coming on right away. I generally turn the unit off when I feel no cold air, this time I left it on just for curiosity. Any ideas as to what might be causing this new problem

What about the schrader valves--they love to leak. Did this tech tell you the product that he put in, because I've never heard of a product that simultaneously seals a leak during the freon input process. You might start with checking the solder joints with soapy water if the schraders check out OK (also with soapy water).

XenoSapien

There is a product that proclaims to stop leaks in the refrigeration system, I strongly recommend not using these products.If they can plug a hole then what will happen to the metering device (expansion valve, piston or cap flo rater) Only refrigerant and oil should be used .The correct thing to do is find the leak, fix the leak and recharge system, get
A different service company to check operation of compressor , If it were mine I would remove refrigerant charge, pull a vacuum replace liquid line drier and recharge system after I found and repaired leak, it does no good to keep adding refrigerant to system and just have it leak out. It is very hard on the commpressor to run low on charge because the compressor is cooled by the returning refrigerant and if run when low the compressor can and will overheat and then you could have more problems. Believe it or not leaks can be found but it takes patience and the right leak detector .Mike

I agree with ace, the stop leak was a bad idea! Leaks can be hard to find, and sometimes it takes a lot of time, but it can be done. It is a waste of money to continue adding refrigerant, you might as well invest that money into a new system. Call another company, tell them you want the leak found and repaired.