[Supras] R134a pressure switch; buying refrigerant

[Bob]

I gave the wrong information in my last email.

What I should have said is that residual oil in the system doesn't matter
and I should have said to DRAIN THE COMPRESSOR.

I was not thinking as fast as I was typing and I don't type that fast...

In the several AC retrofit clinics I have gone through there wasn't a
conscientious as to flushing the system.  

If the compressor detonated then there wasn't a choice.  The system had to
be flushed and a throw-away filter should be installed to catch the big
chunks left in the system that flushing didn't remove.

It seems like the only seminars I went to that said it was necessary to
flush every system were put on by chemical suppliers that sold flushes....

You draw your own conclusions there but an argument can be made that the
crud that is in the system may be loosened up but not completely flushed out
will just cause the compressor to fail later....

We only flushed out systems with detonated compressors and luckily we never
had a Ford with the "Black Death" in the system 

http://www.ackits.com/index.cfm?fuseaction=black%20death

I know of a shop that if the compressor detonated they would only do the job
if every part if the system was replaced... Evaporator, condenser, lines,
ect...

He is a great mechanic but he doesn't get much work for obvious reasons.

Bob





Bob:

    Your information is the first I've come across ("conversion kit"
ignorance not withstanding) which does not include stern warnings against
flushing to remove mineral oil during an R134a conversion.  There are many
flush kits on the market for this.

    I understand that the proof of the pudding is in the eating, so to
speak, and that much of the mineral oil winds up in the receiver-dryer
resulting in a working system.  I've had occasion to change about 3 dryers
due to leakdown from fatigue cracked condensers or hoses over the years,
including the one in my supra, and did not find significant oil in at least
two dryers where the condenser leak was benign enough to not require much
oil fill.

    The supra compressor is built such that you can take a piece of clean
1/16" wire, and bend it slightly to stick down the suction port past the
swash plate after removing the hose end, and gage how much oil is left in
it.  In all but one case when enough oil was lost that the compressor
siezed, significant oil was left in the compressor.  Since mineral oil is
not soluble in R134a, it does not readily flow through the system with it.
Can't say I know what the effect of that is on performance or longevity.
But if it were me, I'd flush the system and not take chances.  It may be
that enough splash takes place in the compressor to suspend some of the
mineral oil in the discharge stream to seal hose pores, but then what
happens on the suction side, downstream of the expansion valve?  We do know
from general refrigeration priinciples that some oil collects in the
evaporator in addition to the dryer, but if it became at least a partial
"quiiet reservior" for mineral oil, cooling surface area would be reduced.

    Of course it could also be that enough oil was lost during R12 leakdowns
experienced in this thread that the amount left was little enough that the
PAG or ester oil displaced what was left, allowing all of the residual
mineral oil to wind up in the filter-dryer.

    Just my two cents, and one reason I chose to remain with R12 (which
incidentally has been coming down in street price)


                    Bernie



----- Original Message ----- 
From: "Bob" <bob at hairballcreations.com>
To: <berniek at technicaldevelop.com>; "'Jim Wooden'" <Jim at WoodenU.com>
Cc: <Supras at supras.com>
Sent: Saturday, May 06, 2006 9:23 AM
Subject: RE: [Supras] R134a pressure switch; buying refrigerant


> Most of Interdynamics information isn't worth the paper it is written on.
> They say that their retrofit kits will fit nearly every car but it doesn't
> fit a GM or Toyota, I guess the two biggest vehicle manufacturers in the
> world don't qualify as "nearly every car"
>
> Anyway, the oils aren't compatible but the mineral oil seems to collect in
> the compressor and the receiver dryer.  That isn't such a bad thing
because
> just sitting in the compressor it lubricates better than ester or pag oil
> and you should change the drier anyway (not that Interdynamics suggests
> that).
>
> Interdynamics also don't suggest vacuuming out your system before you
> retrofit and that is just plain stupid for so many reasons.
>
> Interdynamics suggest Ester Oil and most of the A/C techs I talk to stay
> away from it. It is kind of a generic one size fit all oil.  I don't have
> any direct experience with ester oil failing but I also haven't heard good
> things either.
>
> The usual rule is that you don't need to flush out the mineral oil because
> it fills the pores on the old style hoses and prevents them from leaking
the
> smaller molecule of R134a. It just takes up space since it doesn't flow
with
> R134a.
>
> Usually a lot of the mineral oil is trapped in the receiver drier it goes
> away with the old unit.
>
> I have converted several Toyotas and I have had good luck. They even work
> fine in Miami Florida. I did change the compressors on a couple of them
but
> that was only because they had failed clutches and it wasn't much more to
> replace the unit vs. the clutch.
>
> Bob
>
> -----Original Message-----
> From: Supras-bounces at supras.com [mailto:Supras-bounces at supras.com] On
Behalf
> Of berniek at technicaldevelop.com
> Sent: Friday, May 05, 2006 10:30 PM
> To: Jim Wooden
> Cc: Supras at supras.com
> Subject: Re: [Supras] R134a pressure switch; buying refrigerant
>
> Jim:
>
>     I'm surprised you made out that well without changing hoses, some of
> which are permeable to R134a.  Hope you got all of the R12 mineral oil out
> of the sytstem, as the oils are not compatible between refrigerants,
despite
> what Interdynamics claims.  I've done some electronic design work for them
> on their air compressor line, and in my opinion, I've never seen such a
> schlock operation (from an old building in Brooklyn).
>
>     Of course, you could also install a manual switch as a short term fix.
>
>
>             Bernie
>   ----- Original Message ----- 
>   From: Jim Wooden
>   To: berniek at technicaldevelop.com
>   Sent: Friday, May 05, 2006 9:14 PM
>   Subject: Re: R134a pressure switch; buying refrigerant
>
>
>   Hey Bernie!
>   THANKS for the tips!
>
>   I think the higher hi-side pressure of R134 may be what broke my HP
switch
> dang it!
>   It was just such a clever way to kick the fans in to boost AC
performance
> - I miss it.
>   I like your suggestion, the R134 is not really that expensive, so I
could
> vent it, quickly replace the switch and then recharge.
>   Even after 20 years, my system is all original (except for some o-rings
> between the condenser and the HP piping that are what caused the
conversion
> to R134a). So I may be on borrowed compressor & dryer time here anyway
> <sigh>.....................
>
>   Thanks!
>   Jim
>
>   At 08:17 PM 5/5/2006, you wrote:
>
>     Jim:
>
>         At least as of last year it was not illegal to vent R134a to the
> atmosphere, as it is not a clorofluorocarbon as R12 is.  Beyond that, the
> temperatures and pressures are different for R134a than for R12.  It may
be
> that your pressure switch is OK, but you may really need one for R134a.
Its
> been a long time since I looked at this, and stocked up on LOTS of R12
> instead of pursuing R134a, having a few old cars.  But you can find the
> information at a refrigerant manufacturer's website, like Forane.  You
want
> the pressure-temperature charts for both.
>
>         (balance snipped to save server space, already posted)
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