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)
8)
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.
Return
to the auto A/C FAQs index
See
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Recharging and
Retrofitting
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