CSC-3000 Series Pneumatic VAV Reset Volume Controllers
4
Applications Guide, Rev G
Adjustments and Calibration
NOTE: Do
NOT
adjust
reset start point and reset
span
(upper and lower knobs)
without
thoroughly reviewing the relevant sections.
Damper Action
The damper action is factory-set at Normally Open
(N.O.). To change to Normally Closed (N.C.), per-
form the following steps:
1. Loosen the damper selection screw.
2. Turn the selection dial clockwise until the “NC”
arrow aligns with the “DAMPER” arrow.
NOTE: Accuracy in the alignment of the arrows is
very important. Make this adjustment as
exact as possible.
3. Tighten the selection screw.
Be sure the
screw is tight
(2 to 4 in-lbs. of torque),
but if
overtightened, the plastic will strip out.
DIRECT Reset Minimum and Maximum
Determining the Type of Reset
The following table shows when Direct Reset or
Reverse Reset is required. Determine the reset type
based on the temperature of the primary air entering
the VAV box and whether the thermostat in the space
is direct or reverse acting.
Adjusting Minimums and Maximums
When adjusting the minimum and maximum airflow
settings, the output responds slowly to changes in
the setpoint. Wait for the flow rate to stabilize after
making an adjustment (usually 20 to 30 seconds) be-
fore making further adjustments. Also, if the damper
position is all the way closed or open when starting
this step, turn the adjustment one full turn, and then
wait 20 to 30 seconds for a change in the flow read-
ing of the Magnehelic gauge. If no change occurs
after this time, repeat until the flow rate changes.
NOTE: The direct reset illustration above assumes
no relays are connected between the
thermostat and “T” port.
For Direct Reset (DA thermostat for cooling or RA
thermostat for heating), perform the following steps:
1a. On the CSC-3000, disconnect the “T” port and
leave it open. Temporarily plug the tubing (but
do NOT plug the port).
1b.
Alternately,
instead of removing the tubing from the
T port, (temporarily) remove the plug from the CSC-
3000’s “G” port.
2. Adjust the LO STAT
∆
P (center dial) one
adjustment at a time until the desired
Minimum
airflow is read at the Magnehelic gauge and is
stable.
NOTE: Adjust the dial no more than about a
half rotation at a time. After making any
adjustment, wait approximately ten seconds
while watching for motion in the damper
shaft. If no motion occurs, make the next
adjustment.
NOTE:
IF the LO STAT
∆
P Limit must be set at
“0” (zero minimum),
do not turn the LO
STAT
∆
P knob fully clockwise. The knob
will adjust one and one-half turns after a
zero minimum is reached. Turning the LO
STAT
∆
P knob fully clockwise will result
in a negative reset condition. This means
that when the controller begins to reset at
the reset start point, it must first overcome
the negative adjustment and will not begin
to reset from “0” until a higher thermostat
reset pressure is reached. This negative
reset will also reduce the effective range
of the controller by reducing the low end
reset, narrowing the reset span. If a zero
minimum is required, adjust the LO STAT
∆
P knob until the controller just begins to
crack the damper open, and then back-off
one-quarter
turn and verify zero airflow.
(This is typically 2-1/2 knob rotations
counterclockwise from the fully clockwise
position.)
Primary Air
Thermostat
Reset Type
Cooling
DA
Direct Reset
RA
Reverse Reset
Heating
DA
Reverse Reset
RA
Direct Reset
Thermostat Pressure
Max. Airflow
Min. Airflow
Reset Start Point
• 3 psig: CSC-3021/3026
• 8 psig: CSC-3011/3016/3017/3025
• 10 psig: CSC-3023
Reset Span (5 psig)
(Cooling w/ DA Thermstat or
Heating w/ RA Thermostat)
