a/c r134-r12 (long)

[shannen]

I've been doing R-12- R-134 retrofits for three summers.  Never had any major
problems with them.  Mineral oil isn't compatible with R-134, but it doesn't do
any damage to any parts, or make any kind of goopy mess, it just collects in
places like the condensor and reciever/dryer.  Here are the guidelines I follow
when doing retrofits.

Dessicant:  Generally cars made after 1987 will have the correct type of
dessicant.  If the compressor has come apart, or there is any contamination
(grey sludge) in the lines, the dessicant should eb replaced.  If the lines
have been left open for a long time, the dessicant should be replaced.  And if
there is any question about the dessicant, replace it.

Since mineral oil isn't soluble by R-134, it won't travel around to lubricate
the compressor.  However, it will be used as a barrier to keep R-134 in the
system.  DO NOT use a flush which will remove all the mineral oil, unless you
want to have R-134  leaking through your rubber hoses and older O-rings.  Use
an oil based flush or if your system is clean, you can use air and blow out
some of the oil.  Actually, GM doesn't recommend flushing any a/c system for
any reason.  Their retrofit bulletin doesn't mention flushing, anywhere, but
mentions using inline filters if needed.  These work well.  I try to remove 50%
of the mineral in the system (replace reciever/dryer, drain compressor, blow
out condensor).

Open the minimum number of fittings/connections necessary to get the job done,
use R-134 compatible O-rings when putting it back together, and coat them with
mineral oil.  I haven't found any need to replace every O-ring in the system.

There are two types of oil which are compatible with R-134, these are PAG and
esther oil.  I prefer esther oils.  I have used PAG oils in GM cars done under
warranty and never had any problems, but PAG oils are similar to brake fluid in
that they absorb moisture.  Esther oils don't do this.  I use the same amount
of oil which was originally installed in the R-12 system, regardless of type.

You will need to install conversion fittings in order to connect the R-134
gauge set.  These are supposed to stay with the car once installed.  The types
I use have red loc-tite on the threads and believe me, they stick.  Some
fittings just piggyback the schraeder valve in the R-12 line, some require it
be removed.

Moisture is the enemy here, so evacuate very thoroughly.  I keep the vacuum
pump running at least an hour, often longer.  Moisture combines with the
refrigerant and forms acid (I believe it's hydroflouric in an R-134 system).
This is what forms the grey sludge in some a/c systems.  This is also the
rationale behind changing the dessicant if in doubt about it's condition.

I start with 80%of the original refrigerant charge, and use outlet temperature
and clutch cycling frequency to adjust the final charge up or down from there.

As with any A/C system, the condensor and evaporator must have good airflow to
work well.  Check for plugging and bent fins, especially on the condensor.
Sometimes an auxillary fan needs to be added in front of the condenser.  I'm
told some older Fords need this, although the ones I have done have worked fine
without it.  Sometimes the pressure cycling switch needs to be adjusted to
allow low side pressure to drop 2-4 psi. (1/4 turn counterclockwise).
Sometimes the thermal cycling valve needs to be adjusted. (I've had to do this
in a combine).  Usually, all is acceptable without these additional changes.

I've done enough retrofits to believe that it's generally easy and, if the
price of R-12 is high in your area, economical.  I charge an additional hour
during a straight R-12 to R-134 retrofit and because of the price difference in
the refrigerant, the customer still pays the same as a simple check/recharge
with R-12.  Yes, this is a long post, just wanted to sharre what works as there
are lots of stories and myths floating around about these retrofits.

Shannen

Scott Schaaf wrote:

> How much OTHER stuff needs to be changed to run 134a?   I heard the oils
> are not compatible,  and the 12 oil will contaminate the 134.   If this is
> so,,, how do you get ALL the old oil out??
>
>                                         Scott...
>
> P.S.  I know this is off-topic,,, could you please e-mail to me directly?
>                         Thanks,   SSchaaf at ERINet.com..
>
> ----------
> > From: mrvette <mrvette at bellsouth.net>
> > To: diy_efi at efi332.eng.ohio-state.edu
> > Subject: Re: a/c r134-r12
> > Date: Saturday, July 04, 1998 9:55 AM
> >
> > > > Op-Amp --> 555 timer)
> > > >
> > > Mat,
> > > since I had a sleepless night (a dumb a** put R134 into my R12 a/c
> > > and did at least $800 worth of damage..) I have been working on a 555
> > > circuit.
> >
> > the adding of r134 nto an r12 system should not, in and of itself cause
> any
> > damage,  it just wont work very well,  unless it is run like that and the
> r134
> > will not pick up the ref. oil to oil the compresser...that is the only
> way it
> > could happen to cause the compresser to self destruct internally....can't
> > imagine anyone running the system that long...
> >
> > Oh well, wonder how that happened?  fellow doing the work used a set of
> homemade
> > adapters?  otherwise the fittings on hoses wouldn't fit....
> >
> > changeovers are easy to do BTW...GENE