Technical information

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REPRI NTE D WITH PE RMISSION FROM RAC ENG IN EER
SUM M E R 2 009
20
TECHNICAL
 The rapidly approaching ban on using
virgin R22 as a Top-up refrigerant has
led to a huge increase in the amount of systems being
retrofied to one of the newer more environmentally
friendly pure refrigerants such as R134a or a HFC-
blended refrigerant such as R407c or R404a.
A major issue with replacing R22 in systems with a
pure or blended HFC refrigerant is that R22 systems
generally operate with mineral oil as a lubricant and
many of the new HFC refrigerants require the use of
polyolester oil. Unless all traces of the previous
mineral oil are removed from the system prior to
retrofing there is a high likelihood of cross-contaminaon,
which could lead to damage to equipment.
The soluon is to use an internal cleaning or flushing
product to ensure that the system is clean before
refilling with new oil and charging with new refrigerant.
I am sure that a number of you can remember
pushing R11 through systems to clean them out, but of
course we live in enlightened mes now and R11 has
long since been banned.
This has lead to a couple of different types of
alternave flushing products entering the market and
these are generally either a circulatory product with a
low evaporaon rate, which is pumped around the
system several mes or a high evaporaon rate solvent
cleaner which is normally a single-pass product.
What do i have to do before flushing?
Remove the refrigerant from the system using a
suitable recovery machine, dispose of through the
correct disposal channels and isolate the electricity
supply to the equipment. Disconnect the compressor
and dryer and also remove or bypass all solenoid and/
or check valves in the system.
Components on bigger systems with large volume
capacity such as liquid receivers, sucon line
accumulators and oil separators can be flushed
separately if preferred and it can also be easier to clean
Internal refrigerant
system and line cleaning
While all types of ushing products used correctly will do the job, it
is a matter of convenience, budget considerations and customer
pr
eference which determines the choice of product, explains
Tom Fitzsimons, product manager at Diversitech/Pump House
the condenser coil, evaporator coil and the
interconnecng pipe work in three separate secons.
How does a flushing product work?
All flushing products will break down the oil, sludge,
etc, remaining in the system following the removal of
the refrigerant and these contaminants are then flushed
out during the cleaning and purging process leaving
behind clean internal surfaces.
Which type of flushing product should I use?
It is important to ensure that the vast majority of product
has been removed from the system by purging through
with nitrogen because these products cannot be removed
with a vacuum pump. It is also important to follow a
manufacturer’s instrucons and recommendaons
regarding this as any excessive flushing soluon le in
the system could lead to contaminaon.
A high evaporaon rate flushing solvent such as
DiversiTech’s DiversiFlush does not require a circulaon
pump because the engineer uses pressure regulated
oxygen free nitrogen (OFN) as the propellant to carry
the product through the system and the kit has a
special re-usable cylinder and injector tool supplied
with the kit. Once cleaned, neat OFN is then used to
flush out any small amounts of solvent that may
remain in the system.
In the unlikely event that there is any le aer that
it will boil off rapidly when evacuang the system
with a vacuum pump. Other high evaporaon flushing
systems may use a pre-pressurised cylinder containing
the cleaning solvent and propellant which needs to be
replaced each me.
Are flushing products safe to use?
It is important to wear suitable personal protecve
equipment, use in well-venlated areas and follow a
manufacturer’s usage instrucons, and familiarity with
the COSHH data supplied. 