First
of all, understand that the reason behind the vehicle manufacturer’s
recommendation NOT to flush the A/C system is that over time, they have
experienced an incredibly high rate of so called warranty compressor failures
due to the fact flush solvent has been left in the system. That’s right.
Residual flush solvent will also kill compressors! So now what?
Understand
what the purpose of flushing the A/C system is and that will help you determine
the best method to use and how to go about the job properly. First of all,
with respect to removing the contamination in the system, you should know
that 99.9% of the contamination is caught up in the oil, not the refrigerant.
Refrigerant taken out of contaminated A/C systems is still basically clean.
It’s the oil that holds all the contamination.
Knowing
that, the key to flushing an A/C system is to remove the oil. That can not
be accomplished by just ‘blowing air’ through the system. The air
has no method of ‘moving’ or removing the debris. When flushing
an A/C system, it’s also important to remove all of the oil and to be
sure that residual flush solvent is removed as well. That means the solvent
must evaporator or dry very quickly; it must not leave a residue (from the
flushing compound itself); it must aggressively remove the oil from the
components of the A/C system.
Before
you start, you should understand that expansion valves, driers, accumulators
and compressors are never flushed. If there are any mufflers on the high
side of the system (between the compressor outlet and condenser inlet), they
will have to be removed or replaced. There is no method of flushing those
mufflers. Above that, the system should be broken down to as many individual
components as possible. Do not try to flush the entire high side of the A/C
system as one long piece with hoses and the condenser all attached. Each
component must be broken down so that it can be cleaned effectively.
When
flushing an A/C system, consider that you are really trying to remove the
oil film from inside a long, long tube. That is only accomplished by using
an aggressive cleaning solvent pushed through the system with pressure (air
pressure or nitrogen). Each component must also be flushed in both directions
repeatedly. Only when the exiting flush solvent remains clear can you be
sure that all of the contamination has been removed.
Typically,
the most important portion of the A/C system to flush is the high side. That
is, the hose from the compressor to the condenser, the condenser itself and
the liquid line running from the condenser to the expansion valve. It is
in this area of the A/C system that all of the heavy contamination resides.
Very little of the debris will be able to pass through the expansion valve
or orifice tube. Only in extreme cases like those caused by ‘Black
Death’ would you need to remove and flush the evaporator.
In
addition to those components on the high side, you should be sure
to flush the suction hose from the evaporator or accumulator, connecting
to the compressor. When compressors seize, it is possible that some of the
debris and broken parts from the compressor travel backwards, up the
suction hose.
With
respect to the evaporator, you should know that in order to properly
flush the evaporator, it must be removed from the vehicle. Removing the
evaporator allows you to assure that the flush solvent gets through the entire
evaporator and that all of the solvent is removed. Remember, the biggest
cause of compressor failures (under warranty to the vehicle manufacturer’s)
is caused by residual flush solvent. By virtue of the way evaporators are
constructed, it’s impossible to remove all of the oil and solvent unless
it is removed from the vehicle. With the evaporator out of the vehicle, you
can turn it and manipulate the component so that you are sure you are cleaning
it properly and that all of the solvent will drain.
Once
the flush is completed and they have been blown dry (using dry shop air or
nitrogen) to remove any residual flush that may remain, each component should
be left open to air for at least 1 hour to assure complete evaporation of
the flush.
When
reassembling the A/C system, be sure that lost oil is replaced and that all
new o-rings and seals are used. The last component to be installed should
be the drier or accumulator. With the system fully sealed, pull deep vacuum
for at least 1/2 hour and recharge the system with the factory specified
amount of refrigerant.
Understanding
the flush procedure, it’s also important to understand what type of
flush solvent should be used. You should always use solvents that are designed
and tested for use in automotive air conditioning systems. Never use oil
based flush solvents, as they will never evaporate completely and they will
always leave some residue. The best solvents utilize virgin solvents (not
reclaimed solvents) and are non-flammable. They will evaporate quickly and
not leave any residue. The COOL ZONE online A/C Warehouse sells
auto A/C flush solvents that
are tested and proven for use in automotive A/C systems.
Flushing
should never be overlooked when servicing auto A/C systems. For more details
and complete procedures, see
Flushing auto A/C systems.
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This
was probably one of the best books on recharging air conditioning that I
have seen...
