Ford did come up with just such a procedure to maintain the A/C system on
their vehicles, about ten  years ago. The solvent that was originally used
in this type of application  was Freon TF solvent.   Liquid oxygen
facilities formerly  used this often to assure the removal of all petroleum
products in aircraft or whatever, because of the explosive potential.   Ford
reintroduced this because they have a truck that has 3 expansion valves and
thus often there is not enough force in the system to push debris out to the
filter dryer.   They also recommended it for  all their vehicles for
whatever reason. It does work but it is expensive as I recall.
  It is most likely the dryer  desiccant   that is spread through this  A/C
system now, the  color would indicate  this is the contaminant.  There are
also some other cleaning systems available for this purpose,  I have seen
air brake alcohol recommended for this purpose, it evaporates and it is very
inexpensive.
  It sounds to me like your mechanic knows what he is talking about.

  hope this helps reassure you;
  Jeff/ Florida

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