TNT You didnt ask for advice on the A/C unit, but I can offer some anyway if you'd like.
The coil freezing up scenario doesnt seem right to me, even if it was, that only indicates a low air flow problem, or a low refrigerant charge. Either way, unless the unit quit working I doubt it needs replaced.
When the evaporator coil is in the attic 99% of the time they lay down on their side. This makes draining the condensation a problem.
The drain on a system like this should consist of the main drain, and the safety drain, which you indicated you had both. The main drain HAS to have a trap in it. If it does not, the system will 'pull' air through the drain (during operation) and not let the water flow. Once the system shuts off the water will drain though.
The safety drain should be attached to a metal or plastic pan underneath the system in the attic. This is put in to insure that water will not leak all over the ceiling in the event that the main drain plugs up. Theres a catch though, the homeowner has to be made aware of these and what they do. hehehhe......
The first thing I would do is take some compressed and air blow through the drain pipes to see if they are clogged. If they are clogged you need to be careful not to put so much air in to blow the fittings apart.
I am skeptical of the 'coil freezing up you need a new unit' scenario. I see things like this everyday where a seemingly good contractor will try to take advantage of an unknowing homeowner, and it pisses me off!! hehehe
Good Luck
Andy