My question is: I know of many apt buildings with older split a/c systems. I know that to replace the cond. unit, you should change the old evap. coil, but that doesn't happen alot. Putting a 10 SEER c/u on these old coils works, but not at the 10 SEER. I have done it b/4 and see it done quite often. Will the problem be compounded any when all changes to 13 SEER. Will it be a more definate "cannot put a 13 SEER on the 6 or 8 SEER coil" or will it also work, just not up to the SEER rating of the c/u. Most bldg owners will want to only change the c/unit. Thanks for any input.