I had these guys out in April and they fixed an internal part, and told me that they looked at the condenser. They said the condenser is all corroded and is leaking freon and told me i need a new compressor right away.
Since I was under warranty for the unit, I waited until June where it was functioning erratically. The person from April came and told me the compressor is still leaking freon and he had to put more in. Further, the compressor is just about dead and i need to hurry up and get it fixed, and he seemed annoyed that I was not willing to spend the $3000 to fix it.
So, right after that visit, I called the company that installed the unit 10 years ago to come out and look at it. His diagnosis was that there is no evidence of freon leak, and he showed me what the coil would look like, i.e. black streaks and there are none. He said he sees no sign of major corrosion beyond normal wear and tear. He said his conclusion is that "it simply looks like a 10 year old unit, and he sees no reason to replace."
So, there is always the questions of who is saying what for whose best commercial interests there is. However, while i tend to believe the original company who installed it, as I know that the units generally last way over 10 years. I may bring in a third opinion, but i tend to feel that he saw where i live, and they felt i could easily squeeze out $3000 for new unit.
My recommendation is that if this outfit gives you a song and a dance for the need for a major repair, that you get another opinion.