Blower Coil Freeze After Compressor Replacement?

Hi,
My in-laws had an exterior AC compressor replaced (by an HD sub-
contractor FWIW...) which worked for a few days, and then ceased
working when a coil leak froze up at the blower (as diagnosed by the
same HD sub-contractor who they called back). He explained that the
problem at the blower was pre-existing, and had nothing to do with
his
original compressor replacement. He's attempting to locate a
replacement coil for the single defective coil, but estimated
replacing all coils which could be necessary if he can't find a
single
coil and could cost upwards of $2K. After they just spent $3k having
compressor replaced.

At the same time the new unit crapped out, they also developed a
thermostat problem at a second unit they have in their attic. That
problem has already been fixed by the same tech. Each unit is
controlled by its own thermostat, but I'm not sure if both systems
could somehow tie together....


I find the timing of both problems suspect (though not unlikely), and
am wondering if they are being sold a bill of goods. Feedback
appreciated!