I get a lot of questions from people wishing to retrofit their R-12 System
to work with the new R-134a refridgerant. I am no expect A/C guy but I
know some guys who are. The guys a www.autoACsystems.com
have written a great article on what is involved in a retrofit job.
Retrofitting auto A/C Systems
Up until the early 1990’s, all auto A/C Systems used a common refrigerant
known as
R-12 (Freon). It was relatively inexpensive and very efficient at transferring
heat. However, it was eventually discovered that R-12 (along with all other
CFC’s and some other substances) had a very sever negative impact on the
earth’s ozone layer. Therefore, R-12 had to be replaced as the preferred
refrigerant.
With most industrialized nations signing the Montreal Protocol (1987), the
elimination of R-12 was imminent. That created a lot of questions and concerns
within the industry. In addition to the concerns about finding a replacement
refrigerant, there was the issue of dealing with all the vehicle A/C systems
that were on the road already using R-12. This created even more questions and
concerns. In order to address all of those existing R-12 systems, it was decided
that they should be retrofitted to use another refrigerant. Once again, more
questions and concerns.
The purpose of this information is to provide you an objective overview of
all the factors that have to be considered when retrofitting your vehicle’s
A/C system. You may not be doing the retrofit yourself, but the information
will help you understand the potential problems and difficulties that can be
encountered. The details will also demonstrate that there really is no such
thing as a ‘closed system’ retrofit where you can just add a can
and go.
When should you retrofit your A/C System? As a general rule, it’s been
decided that for optimum cooling performance, any vehicle A/C system that was
designed to work on R-12 should be serviced with R-12 for as long as the supply
is available. As we move forward in time and supply shortages appear, it is
obvious that pricing will become a major factor in the decision. If you have
to retrofit, most aftermarket professionals feel that the best choice of refrigerants
is still R-134a, and usually only suggest alternative refrigerants when performance
problems are encountered with R-134a.
Some of the factors that have to be addressed when retrofitting the A/C system
include:
1) Changes in refrigerant oil
2) A/C System Flush
3) Change of drier or accumulator
4) Caution with condenser design
5) Caution regarding compressor
6) Cooling and/or cooling fan operation
7) Installation of HPCO (High Pressure Cut Out Switch)
Installation of charge port adapters
9) System Label
Changes in A/C refrigerant oil: As a rule, R-12 systems use mineral oil and
R-134a systems in new vehicles (OE Applications) will use PAG oils. For compatibility
issues, the industry moved to use Ester oil (POE) for retrofitting systems.
Ester oils were chosen because they were shown to be compatible with both the
mineral oil already in the system and the R-134a refrigerant about to be installed.
In recent years, new synthetic lubricants have been introduced that have proven
work well with all oils. They have shown excellent results, improved cooling
performance and have eliminated a lot of the confusion about which oil to use
and when.
Flushing the A/C System: This is usually done in order to remove as much of
the mineral oil (and any other contaminants) in the system as possible. It also
helps to assure against oil overcharging which can reduce cooling performance.
When the system is flushed, the proper amount of new oil can be added before
recharging. If your are considering retrofitting your a/c system because some
other component has failed (ie.: leaking evaporator, compressor failure, etc.)
the system should most certainly be thoroughly flushed.
Change of drier or accumulator: The drier or accumulator is the one part that
should always be replaced when retrofitting. First of all, it provides filtering
for the refrigerant and (most importantly) removes moisture. Doing a retrofit
without it would be like changing the engine oil and not changing the filter.
Secondly, new replacements will (almost always) be manufactured with either
XH-7 or XH-9 desiccant. These are compatible with R-134a while the desiccants
used in R-12 systems may not be compatible.
Caution with condenser designs: Although R-134a is an efficient refrigerant,
it is not as efficient as R-12. In many older R-12 systems (pre 1980), the original
condensers were manufactured in a round tube (usually 3/8” O.D.) and flat
fin design. These design configurations usually do not work well with R-134a,
and you may have to replace the condenser with a newer design configuration.
The replacement condenser should be either an aluminum serpentine design (which
incorporates all aluminum vacuum brazed construction) or a parallel flow design
that incorporates smaller tube diameters and higher cooling fin density. It
would not be wise to purchase the OE replacement condenser for your vehicle
as it will probably be the same tube and fin design you already have. Aftermarket
suppliers will be your best source.
Caution regarding compressors: In almost all cases, there should be no reason
to replace the compressor in order to complete the retrofit, unless it has already
failed. The only precaution is for older compressors that will (after retrofitting)
be operating at potentially higher pressures. The higher pressures could cause
other problems or potentially a complete failure. Other than those precautions,
it is good practice to remove the compressor and drain as much residual oil
out as possible. (Compressor can not be flushed)
Cooling and/or cooling fan operation: For applications that use belt driven
fans, it is important to be sure that fan clutches (if installed) are working
properly and that all fan shrouding is in tact. For applications with electric
cooling fans, it is important that they be checked so that they are engaging
at the proper time to help eliminate excess high pressure conditions. Additionally,
a general cooling system inspection is good practice. An overheating radiator
can (and will) reduce the ability of the condenser to dispel heat, causing excessive
high pressures.
Installation of HPCO (High Pressure Cut Out Switch): This is an excellent safety
mechanism that should be installed. The switches are usually designed to perform
a few functions. Most importantly, they will stop the compressor from coming
on if the system looses it’s charge, and they will also cause the compressor
to shut down (temporarily) should the system pressures get too high.
Installation of charge port adapters: Your system should have ‘retrofit
adapters’ installed on both the high and low side service ports. They
are generally inexpensive and allow R-134a manifold gauge sets to be attached
to the system (for charging and testing). They also provide an instant notification
to the next service technician that the system has already been retrofitted
to R-134a. Be cautious of the fact that many shops will install the adapters
for charging purposes and remove them when they are done. This practice is illegal
in most jurisdictions and should be frowned upon.
System Label: Each A/C system that has been retrofitted should be labelled,
identifying the new refrigerant. Additionally many of the labels allow for the
amount of new refrigerant charged. That is helpful because the total amount
of R-134a will be different from the total factory specified charge of R-12.
Although this information does not cover every example and possible problem
encountered when retrofitting an A/C system, it should provide you a good understanding
of all the factors that have to be addressed.
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