I have a york 4ton/80k btu standard builder grade system. It hit about 13 years old, and the evap coils froze up last week. Had the guys come out and leaks out the yazoo, so the evap coils are dead.

Question now though, (can/do) I just replace the coils or do I get a new system? They want to sell me a new exact size replacement, but with much more efficient equipment.

What I have is oversized for the house, but the ducting is not... optimal. So a properly setup system would be more efficient and comfortable, but then again I wanted another year or two an 9-10k seems like a lot to spend right at the moment.

A quick calc shows:
Total Btu's Cooling
32997
Sensible Load
30643
Latent Load
2354
Total Btu's Heating
64690

In northern VA. I like keeping the temp at 72 winter and 73 summer. I do have a humidifier.

That's fudging a couple numbers upwards since I don't have exact numbers for the walls, but I am probably not getting some other numbers right so I think it balances out. 2100sqft townhouse, one south exposed wall. r13 walls and r30 attic. Fairly tight, but before wrap became a requirement under siding and brick.

Any hints?