CSC-3000 Series Pneumatic VAV Reset Volume Controllers
6
Applications Guide, Rev G
Reset Span
NOTE: In almost all applications, the reset span
never needs adjusting. Do not change the
default 5 psi unless really necessary.
The reset span is the thermostat’s effective reset
range for the controller. A reset span of 5 psi means
that it will take a 5 psi pressure change measured
from the reset start point to reset the flow rate of the
VAV box.
3 psig
8 psig
13 psig
Thermostat Pressure
Max. Airflow
Min. Airflow
Reset Start Point (8 psig)
Reset Span (5 psig)
NOTE: Reset span is the pressure change at “T”
above the reset start point that causes the
flow setpoint to move from one extreme to
the other. In a direct reset application, the
flow setpoint will change from minimum
to maximum flow above the start point. In
a reverse reset application, the reset will
change from maximum to minimum flow
above the start point.
The CSC-3000 series are factory set with a reset span
of 5 psi. This is standard in most applications and
does not typically require adjustment. Leaving this
adjustment at the factory setting is recommended.
If necessary, the reset span can be adjusted (between
0 and 10 psi). If the reset span is changed, the
minimum and maximum flows may need to be
readjusted.
To adjust the reset span to another value, perform the
following steps:
1. Adjust the thermostat to a higher pressure,
beyond working range (20 psi is best).
2. Attach a pressure gauge to the “G” port (requires
5/32" O.D. tubing).
3. With a small flat-blade screwdriver, adjust (coun-
terclockwise to increase; clockwise to decrease)
the reset span control (at the bottom of the con-
troller) until pressure at the “G” port equals the
desired reset span pressure.
3 psig
8 psig
13 psig
Thermostat Pressure
Max. Airflow
Min. Airflow
New Reset Start
Point (3 psig)
Old Reset Start
Point (8 psig)
(Reverse) Reset Start Point Adjusted from 8 to 3 psi
Reset Start Point
The reset start point is the pressure from the
thermostat at which the controller begins to reset
from the LO STAT to the HI STAT setting.
Models of the CSC-3000 series come with reset
start points factory-set at 3, 8, or 10 psi. (See the
chart on the next page.) These are standard in most
applications and typically do not require adjustment.
If a reset start point is needed other than the default
setting, all models are field adjustable between 0 and
10 psi. (If the reset start point is changed, the reset
span may need to be adjusted as well.) To adjust the
reset start point, carry out the following steps:
1. Put the thermostat pressure at the desired start
point pressure (e.g., 3 psi).
2. Remove rubber plug at the “G” port and read
pressure at “G” with a 0–30 psi gauge (requires
5/32" O.D. tubing).
3. With a small flat-blade screwdriver, adjust
(counterclockwise to increase; clockwise to
decrease) the reset start point control (at the top
of the controller) until the pressure read at “G”
port is just beginning to move off zero (0) psi.
NOTE: If the controller does not respond correctly
after all adjustments have been made, it
may be necessary to correct the reset span
adjustment.
