[Supras] R134a pressure switch; buying refrigerant

[berniek@technicaldevelop.com]

Bob:

    Yes, just a few percent of mineral oil will not hurt in an R134a
conversion.

    The filter-dryers I've cut apart were built with sufficient stuffing to
act as good filters.  Flow was from the outiside of the stuffing material
inwards, like an engine oil filter but without the pleating.  The one I
changed on the Supra had small metal chips on the stuffing material surface
which appeared to be washed in from initial manufacture, all on the outer
surface of the stuffing before they could get through the stuffing and into
the expansion valve.  I bought the car when it was two years old, still
under warranty, but the compressor siezed a couple of years later, as I
never had reason to suscpect that oil addition was needed.  After spending
$400 on a new compressor, filter-dryer, matching clutch, and doing a
recharge from scratch, I took apart the old compressor and just found minor
scuffing on the swash plate and follower shoes, despite the fact that the
increase in friction was enough to make the drive belt slip.  I'll bet
dollars to donuts that if I had just added maybe 6-8 ounces of oil,
everything would have been ok after manually turning the compressor shaft a
few times.  But, who knew at the time?

    In one instance after compressor failure in the distant past, I plumbed
in a Parker suction line filter made for stationary applications.  Grainger
used to have good prices on refrigeration stuff, no longer true today.

    The Ford black death is another matter.  From what I've read it comes
from breakdown of fluorocarbon (Teflon or Kel-F) rings on the compressor
pistons, which must really involve high temperatures.  Since Ford used
orifice tubes rather than expansion valves (maybe both in some
applications), the expansion tube mesh acts as a good filter as your
attachment shows.  Never had occasion to cut open a Ford filter-dryer, but
I'd be curious as to why the crud was not caught by it and wound up in the
orifice tube instead.


        Bernie

PS:  I've done flushes in larger through-wall air conditioners, following
compressor burnout, again when Grainger prices on new compressors were
reasonable.  That requirement is different from automobile applicaitons due
to burned magnet wire varnish, etc., getting into the system.  Most such
A/C's use capillary tubing rather than expansion valves, but the larger ones
(above about 18K BTU) I've seen with expansion valves.  One trick is to heat
the expansion valve bulb to force the valve open to allow the flush to flow
without impediment.



----- 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 5:15 PM
Subject: RE: [Supras] R134a pressure switch; buying refrigerant


> 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.
>
(snipped to save bandwidth; balance already posted).