Date: Mon, 26 Jun 1995 11:42:27 -0600
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Steve Cutchen <scutchen@Arco.com>
Subject: Re: Drop in R-12 replacement...
In general response to all on this question, here is some information I
downloaded a while back. A manufacturer had been identified, and this
stuff is supposed to go on sale in September. I also have a copy of
Goble's patent application, if anyone is interested...
- ---Steve
scutchen@arco.com
***Disclaimer***
I have no interest, financial or otherwise, in R-12 replacements other than
the fact that I own two cars which use R-12.
- -----repost (please pardon the rough formatting)------
A DROP-IN CFC-12 REPLACEMENT FOR AUTOMOTIVE AIRCONDITIONING
by
George H. Goble
286 W. Navajo
W. Lafayette, IN 47906
ABSTRACT
There currently exists a large number (millions) of automobiles with
air conditioning systems designed to use CFC-12 as the refrigerant along
with plans to produce such systems into the 1992-1995 time frame. During
the 1992-1995 period, new production will transition to HFC-134a
refrigerant based systems or other technologies which offer zero or little
ozone depletion. CFC-12 based systems will finally cease production around
1995, but they will have a lifetime of about 10 years, extending the need
for CFC-12, or a substitute until the year 2005 or so. This paper will
present a ternary blend of refrigerants which may be able to be used as a
transition refrigerant in CFC-12 designed automotive air conditioners until
HFC-134a and other technologies are able to take over. Performance, oil
miscibility, flammability, toxicity, and testing with a commercial
dehydrant/leak sealant will be discussed.
INTRODUCTION
A ternary blend of HCFC-22, HCFC-142b (chlorodifluoroethane), and
small amount of R-600a (isobutane) has been found to provide acceptable
operation on several automobile airconditioning systems designed for use
with CFC-12. Some capacity increase has been noted in most systems,
probably from the blend being non-azeotropic, leading to better utilization
of the condenser and evaporator [1]. This blend features 95% less ozone
depletion potential (ODP) than does CFC-12 (ODP of 0.05 vs CFC-12 with ODP
1.0). This blend is 55% HCFC-22, 37% HCFC-142b, and 8% isobutane by weight
and is compatible with mineral oils currently used in CFC-12 systems.
Testing began in August 1990 in two vehicles, a 1990 Pontiac
Transsport, and a 1978 Datsun 810. A 1979 Grand Prix was added in October
1990. By July 1992, some 500 vehicles were running this blend. Only one
failure has occurred. A 1984 Buick Century had a DA-6 compressor fail. The
tear down of the compressor revealed the thin Teflon piston rings had
broken, and fragments had lodged in the valves, holding them open. Local
mechanics state this is an extremely common failure mode for this
compressor (with R-12), and one mechanic reported he changed 38 DA-6
compressors in a two month period during the summer of 1991 which had
failed for the same reasons. The remaining intact Teflon piston rings, did
not appear to be swollen or affected by this blend. Currently, there is no
reason to suspect this blend as being the cause of this failure.
The first two vehicles were instrumented with gauge manifolds (all
copper lines) in the passenger compartment along with thermocouple probes,
so temperatures and pressures could be monitored in real life driving
situations. The 1990 Transsport, ran the standard CFC-12 charge for the
first year of its life, it then was charged with the ternary blend. After
8 months no loss of charge was noted from performance and pressures.
Refrigerant has remained clear and dry as observed in an installed liquid
line sight glass.
PERFORMANCE
Testing of this blend has shown significant (around 4F-13F) decrease
in discharge air temperatures at ambient temperatures over 80F over that of
what CFC-12 did. Condensation and evaporation of the refrigerant appear to
occur over a larger band or "glide", thus achieving better utilization of
the evaporator and condenser. At lower ambients, the capacity (cooling) of
this blend drops off to approximately that of CFC-12, mostly from the
reduction in head pressure. Different systems perform differently. CCOT
(orifice) systems generally show more increase in capacity than do
expansion valve systems. Compressor discharge temperatures did run slightly
higher than with R-12. Hot ambients (90-100F) days produced discharge
temperatures in the 180F range. The same systems had R-12 discharge
temperatures in the 160F range (average city driving). Even though slightly
higher, the compressor discharge line temperatures are still low enough to
prevent refrigerant/oil breakdown.
OIL MISCIBILITY
In addition to refrigeration effect, the isobutane makes this blend
miscible in standard mineral oils used in CFC-12 systems. Neither HCFC-22
nor HCFC-142b by itself are very miscible with mineral oils used in CFC-12
systems at evaporator temperatures (32F). The "Upflow" evaporators and
large diameter suction lines commonly found in R-12 systems may cause
problems with oil return to the compressor, resulting in compressor
failure, when the refrigerant is not miscible in the oil being used [2].
This blend stayed dissolved in oil (20% oil) by volume, at 32F (approximate
evaporation temperature in auto A/C systems) with Suniso 5GS (525 SUS
viscosity) mineral oil of the type used in auto A/C systems. Suniso 3GS
(150 SUS viscosity) mineral oil (naphthanic) and Virginia KMP 150 viscosity
mineral oil (paraffinic) also stayed dissolved in refrigerant at 32F. Both
150 viscosity oils were completely dissolved at 0F. Around 10% (by volume)
of Suniso 525 SUS viscosity oil dissolved in the refrigerant at 0F. This
525 viscosity oil is normally used in auto A/C systems which only operate
at 32F or higher. Typically, around 10% by volume, oil is circulated with
the refrigerant in auto A/C systems.
FLAMMABILITY
The current blend could not be ignited, even after a 4 month leak down
test (over 1/2 the charge had been lost). It should be noted that even
CFC-12 can be "flammable", when it contains dissolved oil, and a rapid
release occurs. The oil atomizes into a fine mist and can be ignited. It
has been reported that HCFC-22/HCFC-142b mixtures are nonflammable up to
concentrations of 68% weight of HCFC-142b [3].
Many "nonflammable" refrigerants, which contain hydrogen atoms, can
become flammable if mixed with large amounts of air under pressure. Such
examples include HCFC-22 and HFC-134a. For this reason, this blend and
other refrigerants and blends containing hydrogen atoms should not be
diluted with air, and pressurized (such as for leak testing). Diluting the
refrigerant with dry nitrogen is ok.
Being a non-azeotrope, this blend will change composition during the
leaking process. Recharging (topping off), systems with partial charges is
prohibited. The entire charge must first be removed, and a recharge done
with new (non recycled) material. Repeated topping off of leaking systems
could lead to this blend becoming flammable, thus the requirement of always
doing a full recharge with new material. This requirement should not
impact automotive air conditioning severely. This difficulty rapidly
becomes prohibitive in large commercial systems, where topping off leaking
systems is the normal mode of operation. Non-azeotropic blends will be
cumbersome in anything except automotive and small systems due to the
requirement that the whole charge be removed. Reconstitution of leaking
non-azeotropic blends to known composition is beyond the scope of almost
all service technicians.
TOXICITY
Unlike the new generation of "hyperfluorinated" refrigerants, all of
the ingredients of this blend have existed for decades and their properties
are well known. HCFC-142b is commercially available in large quantities.
LEAKING AND LEAK SEALING IN CARS
It has been observed, that a large percentage of older (4 years or
older) cars, seem to have continual slow refrigerant leaking problems.
Even when the leaks are identified and repaired, many are low on charge by
the following summer. New leaks form, and/or hose diffusion may be
occurring and may be undetectable due to the large surface areas or
difficult to access areas. Airconditioning service shops, often can only
repair "obvious" leaks or change "bad" components. Some leaks have been
observed to be temperature sensitive (e.g. only leaks in the winter when
parts contract) Many cars are continually recharged at 2 month to 1 year
intervals, since the leaks are impossible to find/repair. Many owners of
older cars are not willing to pay the cost of an entire new system being
installed (often over $1000), just because the leaks cannot be found and
repaired. State laws are being enacted (such as Florida, 7/1/91), which
prohibit automobiles from leaving a service shop unless the leak is
repaired. If the leak is not repaired, then the CFC-12 must be removed from
the system before releasing the car to the owner. Mechanics have reported
to the author that they have encountered certain brands of connectors which
always leak small amounts of charge, even if they are new and this has led
to much frustration as they cannot be properly "fixed".
A commercial dehydrant/sealant, "DRY-PAK" and "CRYO-SILANE" made by
Cryo-Chem International [4], have been tested with this blend at higher
dilutions than their normal product. System drying and sealing of leaks
has been observed to be satisfactory for the three week to 1 year "leak
rates". This also stopped diffusion through hoses and helped prevent
composition changes in the blend due to leaking. Elimination of constant
recharging reduces the "effective" (per car) ODP further. If a car "saves"
five additional recharges in its lifetime, then the effective ODP becomes
0.01 for a 99% reduction in ozone depletion from CFC-12. The sealant cost
per car works out to be less than $20. Shaft seal leaks are not repaired,
but they are reduced. Use of this sealant requires the system be "dry",
with no significant moisture trapped in the drier. The sealant
manufacturer requires that the drier be changed prior to use. Experience
has found this to be true. Using this blend [with sealant] on "wet"
systems (without changing the drier), resulted in the sealant being
neutralized and no sealing action. No harm was caused be this action other
than sealant being wasted. The systems continued to perform (and leak)
normally. Changing the drier and orifice are always good refrigeration
practices. Old driers can have their desiccant bags break, clogging the
system with clay from the desiccant binder.
PROCEDURES
Being a non-azeotropic blend, certain procedures must be followed to
prevent composition changes. The most obvious is that the system must be
"liquid charged", carefully to avoid slugging the compressor. Systems with
partially leaked charges, should be discharged before recharging, to
achieve a known composition. This problem is greatly reduced by the
addition of the above sealant. Under the "1990 Clean Air Act", this blend
cannot be vented to the environment after certain dates (mostly in 1992),
depending on the type of service (mobile airconditioning, fixed, size of
service shop, etc). It can be "recovered" (pumped into a tank) with CFC-12
recovery equipment and returned to the manufacturer to be reclaimed to new
standards or be destroyed, it cannot be reused on site.
CONCLUSIONS
The author believes this blend can be used to keep existing and future
CFC-12 automotive airconditioning systems running until they reach their
normal end of life. This blend may take some pressure off the race to get
HFC-134a, its complex lubricants and field procedures operational, for
retrofitting existing CFC-12 systems which fail in the field. Being a
blend, "custom" refrigerants can be made for extra performance in hot humid
climates with minor system modifications (a high pressure cutout switch).
Testing is currently ongoing in this area. It is possible to deliver
subfreezing air continuously at ambients of 100F (highway driving).
Patent pending.
REFERENCES
[1] Kruse, H. "The advantages of non-azeotropic refrigerant mixtures
for heat pump applications" Int. J. Refrig. 1981 vol 4 May pp 119-125
[2] ASHRAE, 1984 Systems Handbook, pp 29.11
[3] Kuijpers, L., Miner, S., "The CFC issue and the CFC forum at the
1988 Purdue IIR conference", Int. J. Refrig. 1989 vol 12 May pp. 123
[4] Private communication with Packo, J., Cryo-Chem Intl. Inc.
------------------------------
End of mazda-list digest, volume 950627
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