I have a 1994 C280. A/C has always been fine. I had it checked about 10 days ago, because it was not as cool as it used to be and we're having a heat wave & temps around 105 in NC. The shop told me they put 2 lbs of freon in it and I might have a small leak on the evaporator core. After I got it back from the shop, it was cool for about 2 days and now nothing ! it just blows regular air, no matter what temp I set it on. The shop said the evaporator needs to be changed, therefore the dash has to be taken out, and it'll cost $1,500 - $2,000...
I've gone thru many posts on this forum this time and in the past and decided to join to get another opinion. Any suggestions about what could be the problem ? I just know enough about cars to be able to change the oil

, but if there are some things I can check to isolate the problem, I can do it. I read about Klima ? relay ?, accumulator with a cracked sight glass that resulted in the same problem I have,... what else ? Thanks