If my air conditioning can be fixed without a large expense? on 2006 Dodge Grand Caravan

I took my car in for a check and they said that there was a leak in the air conditioning system. Not sure where [front or rear]. They added 2.4 lbs of freon. It worked before I left but two or three days later [when it was hot] it didn't. Isn't there some kind of sealant that is put through the a/c pipe to close the leak?

I would recommend asking the shop to check the hoses and the high and low side valves. A leak in those areas could be repaired without a large expense. A condenser, which is also a likely failure, would be the next least expensive failure. I would not recommend any kind of sealant for three reasons: First and foremost, you can very easily create even bigger problems than you already have. Second, If you leaked out all of your refrigerant charge in three days, it isn't likely that a sealant would work anyway. Third, sealants generally work best on o-ring leaks, which is usually the cheapest thing to fix right. About the only time that a sealant might be a viable option would be if the leak is at the compressor shaft seal.
Unfortunately, if the leak is somewhere else, like an evaporator core, then you are looking at a major expense.
What do you mean by a "major" expense?I received an estimate of 1100.00 to replace the evaporator core, the rear ac line assy, add refridgerant and dye. Can the job be done cheaper by using the kit#CNTKX210AA