Thermostatic Expansion Valve (TXV) Adjustment Procedure
NOTE: THE FOLLOWING INFORMATION WAS OB-
TAINED FROM SPORLAN ENGINEERING BULLE-
TIN 10-11. IT HAS BEEN REPRINTED HERE WITH
THEIR PERMISSION. IF MORE INFORMATION IS
REQUIRED PLEASE CONSULT THAT BULLETIN.
The thermostatic expansion valve is erroneously con-
sidered by some to be a mysterious and complex de-
vice. As a result, many valves are needlessly adjusted
or replaced when the cause of the system malfunction
is not immediately recognized. Actually the TXV per-
forms only one very simple function. IT KEEPS THE
EVAPORATOR SUPPLIED WITH ENOUGH REFRIG-
ERANT TO SATISFY ALL LOAD CONDITIONS. It is
not a temperature control, torque control, suction pres-
sure control, or a control to vary the compressor's run-
ning time. How effective the valve performs is easily
determined by measuring the superheat as outlined in
Diagram A.
Checking the superheat is the first step in a simple and
systematic analysis of TXV performance. The following
adjustment procedure is for the unlikely event that the
TXV will require a field adjustment. Before attempting
any adjustment, please verify that all other possibilities
have been checked.
It has been found that in almost all circumstances, a
TXV adjustment was not the problem. It was a symp-
tom of another problem (examples: improper brix level
of the product, worn or improperly installed scraper
blades, improper torque settings, improper refrigerant
added to the unit, a refrigerant leak, etc).
As you can see by this brief list, alot of other things
should be checked before deciding a TXV adjustment
or replacement is
required. The adjustment proce-
dure is as follows. NOTE: The unit must be operat-
ing with a properly brixed product to check super-
heat. DO NOT ATTEMPT TO READ SUPERHEAT
AND SUC-TION PRESSURES WITH NO LOAD ON
THE REFRIG-ERATION SYSTEM.
1. Remove the right side panel (as you face the front
of the machine).
2. Before attempting any adjustment, determine what
the superheat is. Install your refrigerant gauges on
the suction access port on the dispensing head not
at the condensing unit read and record the suction
pressure while the unit is running right before the
unit cycles the liquid line solenoid off. Next measure
the suction line temperature as close to the TXV
suction bulb as possible and record this information.
Now convert the suction pressure to temperature
using a temperature pressure chart (Diagram C),
the refrigerant in this case is HP-62 (R-404A). Now
subtract the pressure converted to temperature
from the actual suction line temperature you meas-
ured. The difference is the superheat.
3. Compare that with what the superheat was when
the unit was installed. This should have been
noted on the operators manual and inside the
unit at the time of install. The superheat and the
suction pressure recorded at initial start up are
best for comparison. If in the event that this was
not done, the suction pressure right at the com-
pressor cycling off will be between 27-35
psig.
The superheat will be around 15°-20°
F.
depend-
ing upon the ambient and load conditions
(Settings apply to single head installs only).
4. Remove the superheat adjustment stem cap
(Diagram
B).
To reduce the superheat, turn the
adjusting stem counterclockwise. To increase the
superheat turn the adjusting stem clockwise.
When adjusting the valve
,
make no more than
one full turn at a time and observe the change in
superheat closely to prevent overshooting the
desired setting. Allow plenty of time between ad-
justments for the new balance point to be estab-
lished. As much as 30 minutes or 6 complete
compressor cycles may be required to seek its
new balance point.
5. Record the system suction pressure and super-
heat right at the point that the unit cycles off the
liquid line solenoid valve. Be sure to place this
information in the space below. This will serve as
a record for any future references.
6. Replace the superheat adjustment stem cap. Be
sure to snug the cap down. Remove your
gauges and install the suction access port cap.
Now install the side panel.
System Pressure & Superheat Record
Date
Superheat
Suction
Pressure
Technician
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