[Supras] Refrigeration service

[Bob]

Bernie

Your right, mineral oil doesn't mix with r134a and in a perfect world no one
would be converting R12 systems to 134a.

That being said real world experience had changed the opinions about
conversions.

It would be nice to replace the hoses but it turns out the mineral oil
saturates the hose and works as a barrier to the 134a leaking out of the
hoses. There may be some leakage but given that even the best system leaks
somewhat the amount that comes from the hoses is minimal

I have been through several A/C clinics put on by Four Seasons and they
don't think that mineral oil hurts a converted system.  They suggest
removing as much mineral oil that you can but their opinion is that the some
mineral oil sitting in the compressor helps.  Even though it doesn't flow
with the refrigerant just it being there seems to extend the compressors
life.  One instructor actually suggested adding an ounce of mineral oil to
new compressor even on 134a systems.

I think one of the bigger worries that our systems have seems to be
disappearing oil.  I have pulled two Toyota systems apart and even though
they were supposed to have a substantial amount of mineral oil in them
neither the compressor nor receiver drier had anything to speak of.

Though I can't prove this it seems like the oil is leaking out with the
Freon and since shops just replace the Freon but never replace the oil that
leaked out.  After a few years of just replacing the Freon the oil level
just drops

The Toyota TSB for A/C Retrofit is here
http://www.cygnusx1.net/Supra/TechTips/R134a.aspx

Bob


-----Original Message-----
From: supras-bounces at supras.com [mailto:supras-bounces at supras.com] On Behalf
Of berniek at technicaldevelop.com
Sent: Thursday, March 01, 2007 10:58 PM
To: jdc25180 at cmsu2.cmsu.edu
Cc: Supras at supras.com
Subject: Re: [Supras] Refrigeration service

PS:  Under NO circumstances is any of the mineral oil used as a compressor
lubricant used in R-12 systems to be left in the system if an R-134a
conversion is done.  It is not easy to remove all of the mineral oil, since
it circulates in the system with the refrigerant.  Mineral oil is NOT
soluble in R-134a, not a good happening since the compressor requires oil
mist circulation, with most of the oil in the compressor sump.  The popular
conversion kits that say the mineral oil "goes to a place in the system
where it will not be harmful" is bogus.  It winds up in the evaporator, the
cooling chamber, where it reduces active surface area and thus cooling
capacity.  There is no really good reason to convert to R134a.  Some hoses
have to be changed because they are 134a permeable (smaller molecular
structure of 134a than R-12).  Getting all of the mineral oil out of the
system correctly requires disassembly, and flushing out the condenser,
evaporator, compressor, etc,. before installing so-called polyalkaline
glycol (PAG) or polyester oils which are R134a compatible.  

            BernieK
  ----- Original Message ----- 
  From: berniek at technicaldevelop.com 
  To: jdc25180 at cmsu2.cmsu.edu 
  Cc: Supras at supras.com 
  Sent: Thursday, March 01, 2007 10:41 PM
  Subject: Re: Refrigeration service


  Darren and list:

      Refrigeration service is not difficult or mysterious once the
fundamentals are understood.  Take some alcohol on your hand, blow on it to
make it evaporate, and your hand gets cold.  Refrigerant works in a similar
way.  You evaporate a liquid in the system by dropping the pressure through
a valve which allows expansion (the expansion valve), and the so-called
"latent heat of vaporization" drives down the temperature, since the liquid
boils at a lower temperature once the pressure is let down through the
expansion valve.  You then compress the vapor, cool it in the condenser to
liquify it (like condensing steam to water from a teakettle on the back of a
spoon) and evaporate it again.  The cycle repeats.  

      If you have a vacuum pump and bell jar, you can place a cup of water
in the belljar and make it boil at room temperature once you lower the
pressure by pulling a vacuum.  Refrigerant works the same way but at a
higher pressure, to pull heat out of the evaporator by boiling at a much
lower temperature than water does.  Latent heat of vaporization of water
pulls heat out of a pot of boiling water, so the temperature cannot get
above 212F (at sea level), but refrigerant does the same thing at a much
lower temperature as stated.  If you turn up the heat under a pot of water,
it will boil away faster, but the temperature does not increase.  

      There are several classes of refrigeration technician licenses.  As of
about 18 months ago, you could study and take the exam over the internet for
car service, which interestingly enough will let you buy all refrigerants,
even those used in fixed applications.  The site to go to for that is
www.epatest.com.

      You wil then need a vacuum pump, gauge set to read high and low side
pressures (suction and discharge of the compressor) and miscellaneous
accessories like an oil injector.  It will cost a few hundred dollars, but
these are tools you will have all of your life.  Just so you know, R-12 and
R-134a take different hose end fittings.  If the EPA has not changed the
rules, you can also buy R-22 to recharge your home air conditioner, even
window types.  I've done a couple of those, using charging fittings and
small copper tubing soldered into a hole punched in the copper suction line
of the compressor.  The fittings and such are available on the internet of
from Grainger.  

      One consideration:  NEVER let moisture into the system.  Once it is
opened, it should be capped off.  If you are charging a system from scratch,
you will need to pull a deep vacuum to get all of the water vapor (and any
residual air) out of the system.  You are supposed to recover refrigerant
according to EPS rules, but I don't think the refrigeration police are going
to come to your garage.  Technically, you can recover used refrigerant in a
propane cylinder as long as it is painted the right color and has the right
fittings.  If fact, the on-line license test is mostly about rules such as
that.  

      One look on ebay shows that the price of R-12 is coming down.  Wish
I'd sold some of mine when the price was higher.  Legally, you do need at
least the on-line license to buy the stuff.  

              BernieK
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