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Is It Cold Enough For You ?
Here is a good winter time project for
those of you that travel less during the
winter months. Check your dash heater and air conditioning system
and perform any needed repairs and up grades. Zay Brand and Duane
Simmons wrote and presented an excellent seminar in 1994 on the
design
and operation of the four air flow system configurations (see
Zay, 310-598-5028, or Duane, 714-633-4731, for reprints). Tips
included:
1) Checking all vacuum controls and lines. 2) Replace deteriorated
foam seals on the temperature and re-circulation doors.
3) Check the vacuum water valve to be sure it cuts off the flow
or add a manual ball valve in series.
4) Modify the air flow on 75 an 76 systems to provide 80% re-circulation
rather than 100% outside air.
5) Add a second evaporator unit in the drivers area in parallel
with the under dash unit.
If your air conditioning system needs recharging it probably needs
repair. In fact, in Southern California and some other states,
certified technicians will not recharge a system without performing
a leak check and repairing any leaks.
With the ban on manufacturing R12 Freon (CFC-12), what are the
current alternatives for the do-it-yourselfer (DIY or the shop
technicians? First, it is illegal for any one to discharge any
of the current refrigerants into the atmosphere. A recovery system
must be used. It is possible for the DIY to make a simple recovery
system, but that is a subject for another Tech Center.
The most straight forward solution is to have the system repaired
and recharged with R-12 at a trustworthy shop. Even at the current
price of around $25-$30 per pound this is not a bad deal. R-12
will be around for some time, only the manufacturing has been
banned. That, coupled with an increasing excise tax will cause
the price to go higher, but supplies are expected to be available
for some time.
Another alternative is the use of one of the EPA approved so
called "drop in" substitutes that are shown in Table
1. The EPA approval simply means they are
safe and does not speak to performance. These are not really "drop
in" and require fitting changes and labeling. These also
require recovery of any residual R-12. In addition, the availability
may be regional or even specific to certain shops, creating a
potential service problem.
Acceptable Substitutes for Air Conditioning under the Significant New Alternatives Policy (SNAP) Program as of May 22, 1996:
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Motor Vehicle AC uses |
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If your system needs major repairs such as a new compressor,
than an excellent approach is the conversion to R-134a. The performance
is slightly reduced, say 3-4 degrees because of the higher vapor
pressure, but if one can make some of the changes outlined by
Zay Brand to improve overall performance. Conversion to R-134a
involves the following considerations as outlined by the EPA Significant
New Alternative Program (SNAP): According to EPA regulations,
the use of any alternative refrigerant to replace R-12 requires
at a minimum that:
-- unique service fittings be used to minimize the risk of cross-condition
of the air-conditioning system or the service facility's recycling
equipment;
--the new refrigerant be identified by a uniquely-colored label
to identify the refrigerant in the system;
--all R-12 be properly removed from the system before filling
the system with an alternative refrigerant; and
-- separate, dedicated EPA-approved equipment be used to recover
the R-12 from the system.
In addition, alternative refrigerant blends that contain R22 must
be used with barrier hoses [these are high density, extremely
low permeability hoses].
PAGs vs Esters.
The mineral oil used with R-12 cannot be sufficiently transported
throughout the a/c system by R-134a. Automobile manufacturers
tested both PAGs and esters for refrigerant/lubricant miscibility,
lubricity, chemical stability and materials compatibility. In
the process of developing recommendations, they also considered
the additives and conditioners present in the oils.
Most - but not all -chose to use PAG lubricants in new vehicles
equipped with R- 134a, and are also recommending PAG lubricants
for retrofits. Some compressor manufacturers are shipping new
compressors with PACTs, some with esters, and some are shipping
them empty.
The amount of mineral oil that can safely remain in a system after
retrofitting, without affecting performance, is still being debated.
It was originally thought that any mineral oil left in the system
might cause system failure. As long as the tech has removed as
much of the old mineral oil as possible, any residual R-12 left
in the system should not have a significant effect on the performance
of the system. Removing the mineral oil may require draining certain
components. Unless the vehicle manufacturer recommends flushing
the system during the retrofit procedure, a service tech can assume
that flushing is not necessary. (Although the SAE J1661 procedure
for retrofit includes flushing, SAE no longer believes that flushing
is critical to a successful retrofit.)
When R-134a was first introduced, it was thought that all non-barrier
/ nitrile hoses would have to be replaced during an a/c retrofit.
Early laboratory tests showed that the small R-134a molecules
leaked through the walls of non-barrier hoses more readily than
the larger R- 12 molecules did. In the lab, this caused unacceptably
high leakage rates. More recent testing, however, has shown that
oil used in automotive a/c systems is absorbed into the hose to
create a natural barrier to R-134a permeation. In most cases,
the R-12 system hoses will perform well, provided they are in
good condition. Cracked or damaged hoses should always be replaced
with barrier hoses.
Unless a fitting has been disturbed during the retrofit process,
replacement should not be necessary. Most retrofit instructions
call for lubricating replaced O-tings with mineral oil to provide
this protection.
Compressors
Industry experts once thought that a retrofit would require
compressor replacement. This belief helped create some of the
horror stories about the expense of retrofitting. Now it is routinely
accepted that most compressors that are functioning well in R-12
systems will continue to function after the systems have been
retrofitted.
When a compressor is first run with R-12, a thin film of metal
chloride forms on beating surfaces and acts as an excellent anti-wear
agent. This film continues to protect after the system has been
converted to R-134a. This helps explain why a new R-12 compressor
may fail more quickly if it is installed in an R-134a system without
the benefit of a break-in period on R-12.
A few older compressors use seals that are not compatible with
either R-134a or the new lubricants. Any compressor that has Viton
seals should not be used with R-134a because the refrigerant will
cause the seals to swell excessively.
Of course, any compressor that is not in good shape should be
replaced during the retrofit procedure. Service techs should make
sure that any replacement compressor is approved for R-134a by
its supplier.
Desiccants, Accumulators, Receiver/Dryers
R-12 systems use an XH-5 desiccant, while R-134a systems use either XH-7 or XH-9 desiccant. Some manufacturers recommend routine replacement of the accumulator or receiver-drier with one containing XH-7 or XH-9 during the retrofit procedure. (Any systems with silica gel should also be switched to XH-7 or -9 desiccant.) Others recommend leaving it alone. Manufacturers generally agree, however, that the accumulator or receiver-drier should be replaced if the vehicle has over 70,000 miles or is older than five years, and is opened up for major repair. In that case, the only recommendation is to use the R-134a-compatible desiccants.
Condensers and Pressure Cutout Switches
When retrofits were first studied several years ago, it was
thought that the condenser and perhaps the evaporator would have
to be replaced to maintain an acceptable level of cooling performance
on a retro-fitted system. Now, it is generally accepted that if
an R-12 system is operating within the manufacturer's specifications,
there may be no need to replace either part.
It is true, however, that the higher vapor pressures associated
with R-134a may result in lost condenser capacity. When retrofitting,
service techs should consider how the air flow and condenser design
on the particular vehicle will affect the success of the retrofit.
In some cases, the installation of pusher-type engine/condenser
cooling fans mounted in front of the condenser have improved the
performance of retrofitted a/c systems.
If you haven't replaced any hoses in recent years, Cinnabar Engineering
Inc. is offering barrier hoses and compressors with barrier seals
fitted for R-12 refrigerant, or you can visit your local Hose
Man.
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