Code No. LIT-1900304
Issued February 1, 2009
SYSTEM 350™ APPLICATION NOTE
Night Setback or Setup Using the A350 Temperature Control
IMPORTANT: Use the A350 temperature
control and S350 stage module only as
operating controls. Where failure or
malfunction of the A350 temperature
control or S350 stage module could lead to
personal injury or property damage to the
controlled equipment or other property,
additional precautions must be designed
into the control system. Incorporate and
maintain other devices such as supervisory
or alarm systems or safety or limit controls
intended to warn of, or protect against,
failure or malfunction of the A350
temperature control and S350 stage
module.
open (in the unoccupied mode), the sensor
reading will be artificially shifted upward by the
number of degrees that corresponds to the
added resistance.
System 350™ applications can be used in
conjunction with any commercially available
time clock that has dry contacts (rated to
switch 1V at 1 mA or less) to perform night
setback or setup. The offset from the daytime
setpoint is accomplished by adding a resistor
in series with the sensor (add 4.3 ohms for
each degree (ºF) of offset from the occupied
control point).
Night Cooling Setup
For setup of cooling, the clock contacts are
open during the occupied mode. The
occupied setpoint is adjusted to the desired
occupied control point plus the number of
degrees that corresponds to the resistance
added. When the clock contacts open (in the
occupied mode), the sensor reading will be
artificially shifted upward by the number of
degrees that corresponds to the added
resistance.
Night Heating Setback
For setback of heating, the clock contacts are
closed during the occupied mode. The
setpoint is adjusted to the occupied value and
the sensor reading is correct during the
occupied mode. When the clock contacts
Example Sensor Readings when Using Night Setback or Setup
Examples
Desired
Occupied
Temperature
Desired
Unoccupied
Temperature
A350
Setpoint
D350
Sensor Reading
Resistance
Occupied
Actual
Temp
Unoccupied
Sensor
Reading
Actual
Temp
Sensor
Reading
Heating Setback, ºF (ºC)
70 (21)
60 (16)
70 (21)
70 (21)
70 (21)
60 (16)
70 (21)
43 ohms
Cooling Setup, ºF (ºC)
78 (26)
88 (31)
88 (31)
78 (26)
88 (31)
88 (31)
88 (31)
43 ohms
Time clocks shown in occupied mode.
Heating (Setback)
Cooling (Setup)
Clock contacts closed in the occupied mode for
heating, open in the occupied mode for cooling setup.
Sens.
A350
Y350
S350
S350
S350
D350
A350
COM
To Heating A350
L1 and S350 COM
Relay Contact
120
VAC
Note: Both cooling S350 COM
relay contacts must be
wired to L1.
L1
N
Stage 1
Heating
Stage 2
Heating
Stage 1
Cooling
Stage 2
Cooling
9305002:350setup.drw
9305001:fig1_01
A 43 ohm resistor
will give an approximate
10 F° setup. Resistor
should be mounted inside
the clock enclosure.
Figure 1: Night Setback or Setup Wiring
Note: This method cannot perform cooling setup and heating setback on the same system.
To lock out the opposite function, use a clock with double-pole/double-throw contacts and wire
according to the diagram. The power to the relay contacts performing the function to be
disabled must always be wired to a clock contact that will open in the unoccupied mode.
IMPORTANT: Select a time clock that has
dry contacts and is rated to switch 1V at
1 mA or less. Otherwise use the time clock
contacts to energize a separate relay that
has dry contacts.
The performance specifications are nominal and conform to acceptable industry standards. For applications at conditions beyond these specifications, consult the local Johnson Controls office.
www.johnsoncontrols.com
Johnson Controls, Inc. shall not be liable for damages resulting from misapplication or misuse of its products. © 2009 Johnson Controls, Inc.
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