There is much talk and discussion in certain forums about
how to determine the correct refrigerant charge level for a capillary tube
refrigeration system, but there is only one, simple method that will result in
the perfect charge in a Frigoboast system; the frost-line method. Pressures and
current draw can be monitored to confirm that these are within expected limits,
but there is no better way to guage the refrigerant level than with the
frost-line method.
Frigoboat R134a
charge guidelines
General
The following is intended to be a
guide for a boat operator with average mechanical skills. It will describe what
symptoms to look for in a correctly charged Frigoboat system so that an
evaluation can be made as to whether service is required. No refrigerant gauges
are necessary for this evaluation, and their use is required only for major
repairs and for evacuating the system.
Warning!
Never use, or allow a
technician to use, anything other than pure refrigerant R134a in a Frigoboat
system. Cans of refrigerant R134a with additives must never be used, nor must
stand-alone additives be introduced into the system. These additives include but
are not limited to: leak detecting fluid, leak stopper, dye, extra oil,
conditioner, etc. Serious damage can result from the use of such products, which
are designed for use only in auto air conditioning systems.
Symptoms of correct
and incorrect charge
Correctly
charged system
The Frigoboat systems are capillary tube systems, and
require a precise refrigerant charge to work at maximum efficiency. Too much or
too little refrigerant will result in a systems that will have some cooling
effect, but will not be working to it’s full potential. In a Frigoboat system,
the temperature of the evaporator is directly related to the amount of
refrigerant in the system. There should be enough refrigerant in the system so
that the last of the liquid is evaporating back to a vapor at the very end of
the evaporator, and just as it enters the suction tube back to the compressor.
After running for a time, there should be a slight coating of frost all over the
surface of the evaporator, and there should be no condensation or frost on the
exposed section of copper tube back to the compressor, and no condensation on
the compressor itself. If the system has been installed correctly, the short
length of insulation supplied with the system should be positioned on the copper
tube starting where it exits the refrigerated box. No other insulation is
required, and any extra that has been installed will only cause the system to
run at less than maximum efficiency and may conceal symptoms of an overcharge.
This short length of insulation is installed to prevent any condensation that
may occur as the cold tube leaves the refrigerated box and is exposed to hot,
humid air. In a properly charged system, there should be a “tinny, gurgling”
sound from the evaporator.
Slightly
undercharged system
If there is too little refrigerant in the
system, it will have evaporated back to a vapor before it reaches the end of the
evaporator. Some of the surface will have a coating of frost, but from the point
where the refrigerant has turned all to vapor, the surface will be cold and
sweating. The frost begins at end of the capillary tube, where the liquid
refrigerant is fed into the evaporator. The evaporator will probably sound the
same as a properly charged system.
Seriously
undercharged system
If the system is seriously undercharged, the
refrigerant may exist in the system only as a vapor, and so there will be no
frosting on the evaporator, just a slight sweating and coldness to the touch. In
this condition there will probably be a constant hissing sound from the
evaporator. This sound is important in identifying if the system is undercharged
or overcharged.
Slightly
overcharged system
Too much refrigerant in the system will result in
liquid still evaporating back to a gas past the end of the evaporator and inside
the tubing going back to the compressor. This means that there is still some of
the refrigeration process going on inside the tubing, and there will be a
build-up of frost or ice on the exposed section. If additional insulation has
been added, it may be concealing this symptom and should be removed. The
evaporator may appear and sound normal, but will be at a higher temperature than
desired, resulting in longer than expected run times.
Seriously
overcharged system
If so much refrigerant exists in the system that
it raises the temperature of the evaporator above 32 deg F, the surface will
only be sweating and cold to the touch, resembling an undercharged condition.
But the copper lines leading back to the compressor, and maybe even the
compressor itself, will also be cold and sweating, and there will probably be a
sound similar to a mountain stream coming from the evaporator. This is a
potentially damaging condition as liquid can reach the compressor where it can
damage the valves, since refrigeration compressors are designed to compress gas
only.
