Also, never heard of using a solvent inside the system,

Hello,

Ford motor have that kind of solvent The Way its work is simple
  it is  working with a pump close circuit  with a big filter and a
gallon  of solvent
and some  adapter  to make connections to  the component

the solvent dilute the oil  and bring the metal chip out .
With nitrogen only, you will not remove all the contaminant inside
you need a liquid to transport the metal chip ..
and normally you flush all the component the opposite of the normal flow

And do a minimum of 45 minutes of vacuum ,
expansion valve  don't  like water,
the reason for a good vacuum is for removing the humidity inside the
system
minimum vacuum  29" - 30 " Hg  when you obtain that kind of vacuum ,the
water start to boil

This is the best english I can write

Denis Belisle
85 westy or westfalia 85 :-)
Quebec Canada