OT: Heating and Air guys - I need a hot tip

[steved0x]

My house is an older home built in the late 50s, and the AC system that it has now was installed in 1994, it is a 3 ton heat pump system (located in North FL) - the house is (supposedly) 2200 heated sq ft.

It froze up last night, and today the man came and determine that it is out of refrigerant (the coils were at 20f). I bought the house April 2013, and the system has been working good so far. I don't know when it was last filled but it has been working good so far.

Apparently it uses an older type of refrigerant, and new systems are much more efficient, etc. etc. They say they can add refrigerant now at $75 for the first pound and $45 per additional pound. They say they can only put it in once and then if it leaks out again they can't re-add without resolving the issue. They say it is better at this point to just get a new system.

The existing system is 20 years old... Should I go ahead and get a new system? Or should I pursue trying to nurse some more life out of this existing one? Is there a procedure for searching for a leak and fixing it? What is the service life of a unit like this?

What questions should I be asking? I had a meeting so they are coming back with some quotes on new systems.
Thank you!

Steve