Part 1: The Smart
VOV™ (Variable Orifice Valve), is it the refrigerant
control of the future?
by I.M. Cool
From November/December 1997
© 2000 All Rights Reserved
1a: Refrigerant Basics
¤ Part 2:
The VOV (Variable
Orifice Valve) versus the FOT (Fixed Orifice Tube)
Part 3: The Flooded Evaporator
Part 1 of 3 of series of interviews with Richard C. Kozinski, inventor of the
Variable Orifice Valve
I.M.: Dick, since you are a pioneer in the field of refrigerant
control devices, would you set us up with a little background.
Dick: Sure. Factory installed air conditioning became available
on American built automobiles in the early 1950's. Today it is standard
equipment on most autos and light duty trucks built in this country.
Since its inception, automotive air conditioning has for the most part
used only two types of refrigerant flow controls: the thermostatic
expansion valve (TXV) and, on many vehicles since 1973, the fixed
orifice tube (FOT). For reasons I'll explain later, we introduced a new
control called the Variable Orifice Valve (VOV) to the aftermarket in
mid 1997 as a drop-in replacement for the FOT.
I.M.: What is the VOV?
Dick: The VOV is a pressure actuated valving device which
produces significantly enhanced cooling performance at low vehicle speed
and at engine idle. Compressor horsepower is also reduced at these
conditions compared to systems using a FOT. OEM tests confirm this. The
VOV accomplishes this by simply reducing orifice size at idle and low
speeds as head pressures rise. This produces subcooling and reduces
liquid floodback to the compressor. Physically it is similar in size to
I.M.: Many readers might need a refresher course in refrigeration
basics. Can you be more specific with subcooling, for instance?
Dick: Sure, but if I have to explain how the VOV works I'm afraid
I'm going to throw around many more technical terms. Perhaps, I can
define these terms in a separate writing and fax them to you.
Editor's note: Dick did fax the definitions, and they appeared
along with this part of the series. To read them, click on: Refrigerant Basics. (Note, we've also linked
specific terms in this part for easy reference.)
I.M.: That sounds good, if you don't mind doing it.
Dick: It'll be my pleasure. Subcooling
in this context is defined as the amount in degrees Fahrenheit that a
liquid is below its boiling point. Subcooled refrigerant per pound has
more cooling potential than say refrigerant at its boiling point. And
much more than a mixture of liquid and vapor. Subcooling refers to
refrigerant at the condenser outlet.
Floodback, in this case, is liquid from the suction accumulator flowing
to the compressor. A little is O.K. - enough to get oil back. Too much
and performance, durability, and horsepower are detrimentally affected.
I.M.: Doesn't the FOT system have subcooling?
Dick: Yes, at road speeds but not usually at idle. This is the
major drawback of the FOT. In fact, it allows a liquid - gas mixture to
leave the condenser in many idle conditions, very poor efficiency. How a
FOT actually controls flow over a wide condition range is probably not
in any popular textbook. (Perhaps I can discuss this in greater detail
later.) The FOT is about twice the flow area at idle as it should be.
I.M.: Is the VOV a new concept?
Dick: No, the benefits of a variable orifice have been recognized
for many years by air conditioning system designers. In fact, pressure
actuated valve designs have been built and tested for over twenty years
by the auto and commercial air conditioning companies. But until now
none have been commercialized. Frankly, the VOV patents I have studied
simply won't work in cars.
I.M.: Why not the VOV sooner?
Dick: R-12 systems of the past produced adequate enough
performance with a FOT to keep development of a viable VOV a low
priority. Now, with R-134a, smaller compressors, and poor condensing,
idle performance on many vehicles is very poor. Foreign makers with good
performing TXV systems are gaining market share in the hotter areas of
the country. This is making auto companies seriously consider
eliminating fixed orifice tubes in future designs. Also, reduced
emissions due to lower compressor power will be part of the decision.
Fuel economy should be improved in hot ambient city traffic.
Environmental concerns loom very large today. An emission test conducted
on a 1997 Minivan by Southwest Research Institute showed the VOV
significantly reduced emissions. I can send you the actual results.
I.M.: Can you share some cooling test results with us?
Dick: Sure. A major California police agency has been testing the
VOV for the past two years in the hottest desert areas of the country.
They report a drastic reduction in compressor failures. Idle cooling
performance is improved by 10°F and more. Canine units, which idle for
hours in the desert, report excellent comfort. Previously, dogs required
cooling fans and were still uncomfortable. The agency has ordered seven
hundred VOV's to upgrade their aging fleet because it made economic
sense when potential savings in compressor repair costs were factored
Instrumented tests of numerous newer R-134a vehicles with fixed and
variable displacement compressors show improvement of 5-12°F in hot
ambient idles. Vehicles with poor idle condensing gain the most. Big
Three test results are confidential. Suffice to say I am working with
I.M.: What about R-134a conversions?
Dick: A conversion from R-12 to R-134a on a 1993 Suburban showed
the VOV improved idle performance significantly over the original R-12
system (3°F), and 5°F over the R-134a FOT at 325 psi condensing
pressure. At higher heads the gain was more. Field reports show even
greater gains on other R-134a conversions.
I.M.: Will the VOV give equal improvements in all sections of the
Dick: No, discharge air improvement in cooler more humid regions
such as Florida will not be as great as in hot dry conditions. This is
because some of the capacity gain is used in dehumidification. Comfort,
however, is greatly improved with this dehumidification. Thousands of
VOV's have been sold and reports from installers confirm these results.
I have personally tested the VOV in many vehicles. You usually don't
need a thermometer to see the gain. You feel it.
I.M.: O.K., you have been comparing the VOV against the very
inefficient (as you say) FOT. How does it stack up against a TXV?
Dick: We have compared the TXV against the VOV both in the lab
and in an OEM wind tunnel. The VOV outperforms the saturated cycle TXV
and competes very favorably with a subcooled TXV system. (More
definitions.) The TXV control has a history of failing with dire
consequences. Failing open will slug a compressor into submission, while
closed it will starve it to death.
The VOV has the advantage of a suction accumulator protecting the
compressor against slugging, and it should not fail shut since there is
always a designed-in flow path. Evaporator coil refrigerant distribution
is better with a VOV since the coil runs flooded
(another fax). Compressors run significantly cooler with the VOV due to
some floodback. The VOV differs from the TXV in that most of the time
VOV parts remain stationary, moving only if head pressures rise high
enough. The TXV internal components however, are constantly moving when
the system is cooling. Common sense dictates which is more reliable. The
VOV is not competing with the TXV in the aftermarket and this is perhaps
beyond the scope of your question, so I'll stop.
I.M.: Why not just a smaller FOT?
Dick: The VOV at high ambient idle in our tests doubles the gain
of an 0.057" diameter orifice versus an 0.072 FOT which is used on
most General Motors cars. The 0.057 raises road speed head pressures
exceeding some manufacturer's engineering guidelines. A small orifice at
road speeds increases compressor horsepower (I won't go into the reasons
now). With a small FOT, airflow on Outside air mode is usually reduced
to limit evaporator load so as to manage these higher head pressures.
This forces occupants to run on Re-circulation at elevated ambients to
maintain comfort. A relatively few factory systems use this size and it
is controversial. May I expand on this subject a little more?
Installing an orifice significantly smaller than production intent is
risky for the repair shop without knowing condensing capability at high
speed under controlled high load conditions, compressor discharge
temperature, and charge quantity tolerance. Shops simply don't have the
facilities to run controlled conditions like the OEM have. An
0.057" FOT has about 38% less flow area than a 0.072. At equal
refrigerant liquid temperature a sizable increase in head pressure (and
horsepower) is required to flow enough to still flood the evaporator.
Many accumulators will not return adequate oil if no liquid refrigerant
is present and compressor failure will result due to lack of
lubrication. Running the system on re-circulation will fool the
installer into thinking everything is O.K., but problems surface at high
humidity outside air operation, especially at extreme car speeds like 80
to 90 MPH. Remember, the OEM's know the benefits of a smaller orifice
but in general have stayed between 0.062 and 0.072.
I.M.: What sizes of orifice are in the VOV?
Dick: Significantly larger than 0.057 at full open and
significantly smaller at idle. This is all I can say at this time.
Something I have failed to mention in your previous question on orifice
size is that a smaller FOT requires significantly more refrigerant
charge. Environmentally this is bad since more refrigerant will be
eventually released into the atmosphere. This orifice size is an
oxymoron. I am saying a small orifice reduces compressor idle horsepower
but increases road speed horsepower. In a later writing this will become
more clear. There are also many subtle factors such as compressor
discharge temperature, hose life, clutch cycle rate, etc., which play a
part in orifice size decisions.
I.M.: What do you see down the road for future A/C designs?
Dick: In the near term the VOV is going to fight it out with the
TXV. I feel the FOT will become obsolete as manufacturers strive for the
most efficient, most reliable alternative driven by environmental and
We will probably see more manufacturers introducing variable
displacement or variable speed compressors. There is a move to combine
components by the auto manufacturers such as condenser and receiver in
one assembly. Desiccants will be replaceable.
In the longer term, air conditioning systems may be hermetically sealed
packaged units with more efficient electrically driven high speed
centrifugal compressors possessing great reliability. Electric and
hybrid vehicles will accelerate these developments. Much of this is just
my opinion, of course.
I.M.: Final question. How does the VOV impact repair shops?
Dick: The VOV is an opportunity to increase sales as the
potential audience is going to increase. For example, FOT vehicles which
cool poorly but had no remedy. Police fleets and taxi cabs are prime
targets. People should now not balk at R-134a conversions since cooling
will be increased not decreased. There may be less compressor call backs
if the experience of the major California police organization is
representative. Customers shocked at repair bills will be less hostile
if performance is demonstrably improved. A reduction in emissions will
make public officials happy. The potential fuel savings is in the right
direction for fleet managers.
I.M.: This has been very interesting. I'm really looking forward
to getting your definitions and technical explanations.
Dick: Thank you for the opportunity to discuss the VOV. Thirty
years ago when I developed the FOT it was done in secrecy. Dissemination
of this type of information is very helpful to speed up acceptance of a
new product if people understand it. (End of Part 1, to go to Part 2, click here.)
C. Kozinski Editor's note:
Mr. Kozinski is an automotive HVAC engineer with over 35 years
experience, including over 25 years in commercial HVAC. His masters
thesis in 1967 covered the fixed orifice tube system. He wrote this
while working for Chrysler Corporation. He co-invented the system with
Mr. Ed Bottum, owner of Refrigeration Research. In 1969 he and Ward
Atkinson spearheaded the FOT development while at General Motors. He
later helped develop the system at GM's Harrison Radiator Division. He
is currently the owner of a mechanical contracting firm and is also a
consultant to several companies involved in HVAC component development.