A/C Retro Fit? (long!)

[Djdawson2 at aol.com]

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Jobe,
I would recommend steering clear of the "quick fix" conversion.  There are
several issues:

First, as another lister brought up, there is an oil incompatibility issue,
and for the reasons he stated (except it's called PAG or POE oil, not TAG).
The mineral oil used in R12 systems is not miscible in R134a, and therefore
will not return to the compressor properly, and usually leads to rapid
compressor failure.  If you retrofit, there is a good chance that chlorine
residue will be left behind (R12 is a CFC), and when you retro to R134a (an
HFC) and change to PAG oil, that oil is susceptible to failure due to the old
chlorine deposits from R12 use.  So, if you do a straight conversion without
significant effort to flush and eliminate all R12 contaminants, you will
experience compressor failure.  It may be later rather than sooner, but it
will happen (BTDT).

Second, the system was designed with R12 in mind as the refrigerant...
therefore, it was designed around the most critical issues for good system
performance: the evaperation point (boiling) of R12... or the pressure/temp
combination at phase change.  R134a's characteristics are different, and so
are the points of phase change.  You absolutely will not get really strong
results from a straight conversion without at least changing the
restrictor/expansion valve.

If you are set on changing to R134a, you really should do this: replace the
receiver/dryer, replace all o rings, replace the compressor seal, drain/flush
the compressor and refill it with PAG/POE, flush and evacuate the entire
system, replace the expansion valve, and then recharge.  Still, don't expect
performance that would rival the R12.

If that sounds too involved (it did to me) I would recommend changing over to
R406a.  This is a nearly drop in replacement for R12, performs nearly as well
(I get 42 degree air from the dash vents as opposed to 38 w/R12), and is WAY
less expensive than R12.  The "nearly" part of drop in replacement means that
you need to insure that your compressor does not have a "Buna-N" or Butly
rubber seal.  Ideally, the comp seal and all o rings should be Neoprene 70.
You can go for the "trial and error" method... charge it and just see if it
leaks.  At $7 per pound, it's not a huge loss if you discover that it didn't
work.

I have 30lb kegs of both R12 and R406a, and have used both with great
results. The R12 will cost you $790/30lb keg, the R406a $195/30lb keg.  The
biggest thing missed by most shops is a strong evacuation.  They will usually
pull a system down for 10 or 15 minutes.  It should actually be done for an
hour minimum.

Finally, if your system is in a state of discharge, and has been for more
than a few days... replace your receiver/dryer.  It is intended to absorb
moisture, and is very critical to good system performance.  If your system
is/has been open, has been discharged due to leakage, whatever... IT IS SHOT.
 Change it and its seals.
Sorry so long, but HTH,
Dave