The air conditioning in my four month old 08 Impreza has failed.  After
finding the system discharged, the dealer charged it with refrigerant
with a UV tracer, and when I bought it back a few days later told me
that the refrigerant was leaking from the evaporator, and that they
would order a new one to be installed next week.

They also said they the problem could be related to the fact that I have
an aftermarket radio with Sirius installed, and that could have damaged
the evaporator, and if that were the case I would have to pay, though
they would in that case document it so I could go after Best Buy who did
the installation.

This is the same radio and Sirius module that I had in my previous car.  
In the previous car the Sirius module (a Kenwood SIR-902, which is
rather large compared to the current units) was installed bolted under
the passenger seat, with the cable running under the moulding to connect
to the head unit in the dash.  In the current car, they took the lazy
route, and just placed the Sirius unit behind the head unit not really
mounted to anything but just held in place by gravity.

I¹m wondering if mounting the unit this way could damage the evaporator,
or are they just blowing refrigerant, and/or if anyone else here has had
a similar problem?

Thanks for your help.