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Condenser
After-Coolers
___Also
known as
__Suction Line Heat Exchangers (SLHE)
__Evaporator Pre-Coolers
__Liquid Line Sub-Coolers
An
older design, the "Liquid Modulator" contains an
internal receiver-drier, and is an example of a
"can within a can".
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Features a cold gas inlet at the lower side, outlet
at the top side of the can to allow the up-flowing cold gas to
bathe the hot liquid-filled tubing coil within
the can.
Absence of desiccant within the device provides
a clutter-free chamber for more efficient
sub-cooling of condensed liquid refrigerant as
it passes through the coil. Unlike
standard automotive a/c accumulators, it has an
external oil return line which contains a
serviceable metering orifice & screen which
allows manufacturers to size the orifice based
on the btu rating or other criteria. Also,
since there is no desiccant, the unit may be
totally flushed & re-installed by service
personnel.
QUESTIONS
&
ANSWERS
What
is it?
A
Suction Line
Heat Exchanger (SLHE)
improves
the efficiency of
cooling of automotive, residential & commercial
systems air conditioning systems. Essentially,
it improves the phase change in the condenser &
evaporator. The result is greater fuel economy,
lower emissions, lower evaporator temperatures,
and other benefits.
Where are they
needed
?
In high heat &
humidity areas,
where the summer is long and intense. Cooler
climates don't impose the extreme heat loads found along the Gulf of
Mexico where an air conditioner must perform
efficiently for 6 to 8 months a year,
with daily temperatures having an average range of
90-103°F during June, July & August. It is important that the a/c system
be in top mechanical shape. Anything that will
improve its performance is worth considering.
Why are they needed?
Simply
stated, because of the problematic R134a
refrigerant, and below par a/c system components
& designs which don't support that refrigerant
very well. There has been an longstanding
debate among refrigeration engineers regarding
the usefulness of SLHE's, and the consensus
seems to be that they provide the greatest
benefit when used to resolve problems with
refrigerants like R134a, or systems with low air
flow, or inefficient condensers. There are
a few less benefits to their use with more
efficient refrigerants like R12, and R22, but
overall, the device serves to improve the
condenser's effectiveness by further sub-cooling
liquid refrigerant before it enters the
expansion valve. On that, there is little
disagreement.
TECHNICAL STUFF
Condensers,
Fans & Air Flow:
Older style tube & fin and serpentine
type condensers do a poor job of releasing heat
back to atmosphere. Improved designs such
as the 6mm multi-flow and parallel flow
condensers attempt to compensate for some of
the deficiencies of R134a. Other factors
such as lack of air flow due to inefficient
fan clutches, condenser obstructions
(grill, transmission oil cooler), unsteady
refrigerant flow because of fluxuating engine
speeds, etc. remain unimproved, thus continue to plague a/c system
performance. Unfortunately for the
consumer, many car makers still cling to the use
of fan clutches which relate to engine needs,
and ignore a/c high side pressures which can
reach 350-400 psi before engine temperatures are
high enough to engage the fan. No car a/c
system can maintain comfortable cabin
temperatures at those working pressures,
especially in high heat load climates. It
is a hidden problem which technicians are not
trained to recognize. A condenser requires
much more air flow than a engine radiator. Fan
clutch operation should relate to a/c head pressure, not just engine
temperature. Most vehicle a/c systems
cannot keep up with the higher heat loads
experienced along the Gulf Coast during summer
months. We are not aware of any OEM car
manufacturer which publishes the btu ratings of
their a/c systems. If systems were
performance rated, car buyers might not purchase
vehicles with sub-standard air conditioners.
In the cooler northern climates this is not a
big issue, but it is a VERY BIG issue in the
south, but nothing significant is being done
about it, and the public has had to lower its
expectations on their vehicle's a/c performance.
Some car manufacturers have made an attempt to
remedy air flow problems by use of high volume
electric condenser fans to provide air flow
constancy. Their fans are activated by a
high side pressure switch. This is a step
in the right direction, but grill clutter has
not diminished, and when systems are improved,
they are also frequently down-sized which wipes
out any gains. High head pressures plague many systems like a
low grade fever, making the compressor work harder,
and the engine consume more fuel, etc.. The a/c system can be
dying with 350-400 psi pressures while
the engine is running normal temperatures.
How
does an air conditioner work?
Air
conditioning systems technically do not make
cold air, they remove heat (evaporation cycle),
then they must give up that heat (condensation
cycle). The compressor pumps, expansion valves,
and other control devices do basically the same
things they always do, regardless of which
refrigerant is used. But, because of inefficient
evaporators, and condensers, something else is
needed, that is, (a) better heat acceptance during the
evaporation cycle, and (b) better heat
dissipation during the condensation cycle. If
the evaporator picks up heat from the
air, the condenser has to give up that heat.
If it cannot effectively give up saturated heat, it
goes right back into the evaporator,
where
it now has
less ability to accept as much new heat from the
passenger compartment as it should, had it been
properly sub-cooled within the condenser. The result?
Passenger discomfort, riding around in a
half-sweat, because of longer cool-down time.
The vehicle never gets really cold while driving
short distances, and some never get very cold
even on long trips. The greater high side pressures
also cause the compressor to work harder,
reducing its life, and increasing fuel
consumption.
Testing fan clutches:
The most practical way to test a fan clutch
on the vehicle is
to run the engine at fast idle (1500-2000 rpm)
with the evaporator fan on high speed.
This loads the evaporator with heat. It is
now up to the condenser to release that heat
back to atmosphere. Watch
the high side pressure gage. Even on a 95-100
degree day, the reading should correct back to
between 250-275 psi, if the fan is working properly.
If it doesn't, the fan isn't turning fast
enough. Check for blocked air flow through
the grill, condenser & radiator. If there
is (a) no air flow blockage, (b) no missing
perimeter air dams which direct air through the
condenser & radiator, (c) not a refrigerant
system overcharge, and (d) no high side
restrictions, etc, then the fan clutch is
defective. Or, in the case of an electric
fan/s, one or both speeds may not be operating.
About 30-60% of the vehicles on the road today
have head pressures in excess of 300 psi.
In fact, head pressures
can exceed 400 psi while engine
temperature is normal, so for all the driver
knows, everything is ok because the only gage on
the dashboard which relates to air flow is an
engine temperature gage. There is no gage
to indicate excessive refrigerant pressure.
The condenser has its own needs which are not
being met. No air conditioning system can
function properly under those conditions.
A SLHE can greatly alleviate even
those situations.
How does
it work
?
Physically, an SLHE may
be constructed in a variety of ways, but we
offer two designs, both of which have certain
advantages:
(a) a can within a can,
and (b) a coil within a can.
1.
Hot liquid from the condenser goes through
an inner heat exchanger, is sub-cooled, and
goes to the downstream expansion valve or
orifice tube.
2. Simultaneously, cold return gas from the
evaporator goes into the surrounding can
(accumulator) bathing the hot interface with the
cool gas, thus sub-cooling the liquid, enabling
it to absorb greater heat from air passing
through the evaporator.
3. After cold return gas leaves the
accumulator portion of the SLHE, it
returns to the compressor, to begin the cycle
over again. It captures the otherwise
wasted heat absorption capacity of the cold
return gas, and puts it to good use.
4. The condenser is no longer totally
responsible for changing the hot gas back to a
liquid. The greatest amount of heat is found in
the liquid, which is in the lower third of the
condenser & downstream liquid line. In systems
equipped with an SLHE, the liquid instantly releases heat to the
cold return gas, lowering head pressure and duct
temperatures. High head pressures are primarily
the result of excessive saturated heat in the
liquid line & lower third of the condenser.
The device enables the system to compensate for
inefficient condensers, poor air flow, and
greatly reduces high side pressures.
THREE (3) PRACTICAL APPLICATIONS
1.
Retrofitted air
conditioning systems.
The conversion of R12 a/c systems (on an older
vehicle) to an alternate refrigerant (several
types, but usually R134a) has resulted in mixed
results. Performance varies from vehicle to
vehicle, usually between so-so to really bad.
Less efficient evaporators & condensers are the
main reason. The older vehicles struggle to
achieve satisfactory cooling, but even some of
the new vehicles which come equipped with R134a
from the factory have poor cooling. If your
retrofitted vehicle is satisfactory, count
yourself lucky, and maybe your local area does
not experience the heat index found in
cities like Houston, Texas!
2.
Poor cooling R12 systems:
First, fix your automobile air conditioning
system. Put it back in good condition. Find and
fix leaks. Check temperature door adjustments.
For best cooling, always run the a/c in
"Recirculation" mode, also known as "Max Air",
in which case the "outside air door" is closed.
If there are smokers, and you wish to change the
air more frequently, "Normal" setting is used,
but it just means that the evaporator has to
then overcome the hot outside air brought in, so
on hot days, it can't keep up. Don't consider
any device, including our product as a cure for
latent defects, but once the a/c system is in
good working order, it will definitely add a
high degree of extra performance, better a/c
cooling, lower head pressures, especially in hot
conditions. Coordinate the installation of the
device
with the any needed a/c repairs, prior to final
recharging, because the liquid & suction hoses
will have to be custom made. Is it worth it?
Yes!
Examples of Vehicles
having a very bad history of poor cooling
include Dodge Caravans, and Plymouth Voyagers
which use the 6C17 variable displacement
compressor.
Custom vans, suburbans, motor homes and a host
of others, which should be producing 36-40°F
when tested in the "re-circulate" mode @ low fan
speed during fast idle (on non-cycling systems),
or during low idle (on cycling systems) even on
95-100°F days. Some clutch cycling switches will cycle out @ 45°F, thus prevent the
lower temperatures from being achieved, even
with the SLHE, but they can be replaced. So, if
your vehicle is not able to achieve 36-40°F
temperatures, it can, if you are willing to make
the investment.
3.
Refrigerant Based Intercoolers:
It should be
obvious that if air conditioners on the dual evaporators of a
conversion van, voyager, or suburban would
benefit from a
SLHE, so would one of our refrigerated chillers
or intercoolers for use with turbocharged
engines. Replacing an ambient charge air cooler
with one of our refrigerated chillers is like adding
that second evaporator, making it "dual"
evaporator system. There is now a need for
the extra cooling provided by the use of an SLHE.
Refer to our web page on Refrigerated
Chillers/Intercoolers for details.
Caution: On dual evaporative
systems (second evaporator and/or intercooler),
we recommend that special care should be taken to either replace
the factory accumulator with the SLHE, or plumb the
vehicle's factory accumulator in SERIES with the
SLHE, otherwise oil starvation of the compressor
may occur. Plumbing it per the above
instructions will prevent oil from becoming
trapped in the unit with the lowest flow.
THE
NEED FOR CUSTOM-MADE HOSES & FITTINGS Adding accessories like
SLHE's,
or Intercoolers means that custom hoses and
fittings will be needed. Building HOSE
KITS to fit EVERY car or truck is impractical,
because of the great variety of engine
compartment configurations. Therefore, you
must be able to build your own hoses locally,
or let us build them according to your
drawing.
Call our Toll-Free
A/C HOSE HOTLINE
888-740-7039
Information Request Form
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