Johnson Controls System 350 A350A, System 350 A350B Technical Bulletin

System 350™

A350A/B Electronic Temperature Control

The A350A/B Series is an on/off electronic
temperature control with a Single-Pole, Double-Throw
(SPDT) relay output and a Light-Emitting Diode (LED)
relay status indicator. Designed to operate with both
heating and cooling equipment, this control includes an
adjustable differential and an interchangeable
temperature sensor.

As are all System 350™ products, the A350A/B is
housed in a NEMA 1, high-impact plastic enclosure.
The modular design provides easy, plug-together
connections for quick installation and future
expandability.

FANs 930, 930.5, 125, 121

Product/Technical Bulletin A350

Issue Date 0899

Features and Benefits

❑ Modular Design

❑❑❑❑ Plug-together Connectors

and 35 mm DIN Rail
Mounting

❑ Two Standard Models

Cover Wide Setpoint
Ranges

-30 to 130°F (-34 to 55°C) or
90 to 250°F (32 to 121°C)

❑ Wide Adjustable Differential

of 1 to 30F° (0.6 to 16.7C°)

❑❑❑❑ Field-Selectable Mode

Jumpers

❑❑❑❑ Available with Either

External or Concealed
Setpoint

Figure 1: A350 Series Electronic

Temperature Control

Enables stage, display, and power modules to
be purchased and installed as needed

Eliminates wiring between modules and
reduces installation costs

Reduces inventory by encompassing
temperature ranges required to support the
majority of Heating, Ventilation, Air
Conditioning, and Refrigeration (HVAC/R)
applications

Enables the user to match equipment cycle
rate and/or sequencing for a given application

Operates in both heating and cooling
applications

Helps deter accidental and unauthorized
adjustments

❑❑❑❑ Interchangeable

Temperature Sensors

© 1999 Johnson Controls, Inc.

Part No. 24-7664-44, Rev. C www.johnsoncontrols.com
Code No. LIT-930010

Increases versatility and serviceability

1

pplication

A

The A350A/B Temperature Control can be used as
a standalone device or in conjunction with other
System 350 plug-together modules to control single or
multiple-stage HVAC or refrigeration equipment.
Typical applications include:

•

frozen/refrigerated food cases

•

cooling tower control

Setpoint Adjustment

Setpoint is defined as the temperature at which the
A350A/B’s relay de-energizes. Use the Setpoint Dial on
the front of the A350A/B to adjust setpoint. See
Figure 2.

Differential Adjustment

•

beverage/milk coolers

•

chiller staging

•

space temperature control

A typical System 350 Temperature Control
arrangement includes the following:

•

A350A/B Temperature Control

•

S350 Stage Modules

•

D350 Digital Temperature Sensor/Setpoint Display
Module

•

Y350R Power Module (or Class 2
24 VAC transformer)

•

A99B Series Temperature Sensor

peration

O

The A350A/B Temperature Control operates on
24 VAC and provides an SPDT relay output. A front
panel LED lights to indicate when the relay is
energized. Adjustable features include:

Differential is defined as the change in sensor
temperature between energization and de-energization
of the relay. Adjustment of the A350A/B differential is
made using the potentiometer marked DIFF. See
Figure 2 for its location. Refer to Table 5 for
adjustment ranges.

24V
COM
VDC

SEN

DIFF

(Differential

Potentiometer)

Relay

LED Indicator

Figure 2: A350A/B Board Layout and

Setpoi nt

Dial

Module

Connector

Jumper Block

Relay

NC

Terminal Locations

NO

Position

Heating

Cooling

•

setpoint

•

differential

•

heating/cooling mode

IMPORTANT: All System 350 Controls are

designed for use
operating controls. Where an
operating control failure would
result in personal injury and/or
loss of property, it is the
responsibility of the installer to add
devices (safety, limit controls) that
protect against, or systems
(alarm, supervisory systems) that
warn of, control failure.

2

System 350 A350A/B Electronic Temperature Control Product/Technical Bulletin

only

as

Heating/Cooling Mode Adjustment

Heating mode

With
setpoint. The relay and LED indicator will de-energize
as the temperature rises to the setpoint. As the
temperature drops to the setpoint
setting, the relay will energize and the LED illuminates.
Refer to Figure 6.

Cooling mode

With
setpoint. The relay and LED indicator will de-energize
as the temperature drops to setpoint. As the
temperature rises to the setpoint plus differential
setting, the relay will energize and the LED illuminates.

As shipped from the factory, the heating/cooling
jumper blocks are installed in the horizontal (cooling)
position. See Figure 2.

selected, the differential is below

minus

the differential

selected, the differential is above

dd-On Modules

A

The S350 Stage Modules, D350 Digital Temperature
Display Module, and Y350R Power Module connect
together and plug into the A350 via a connector on its
right side. The maximum number of add-on modules is
listed in Table 1.

Table 1: Maximum Number of S350 Stage
Modules per A350A/A350B

Power
Source

Y350R

External
Class 2
Transformer

Note: For each S350P added, the number of S350A

or S350C Stage Modules that can be used
with a Y350R decreases by two. If an external
transformer is used, the number of S350A and
S350C Stage Modules used decreases by
one for each additional S350P.

Number
of S350A
or S350C
Modules

Allowed

96 4

98 7

Number
of S350A
or S350C
Modules

(with

1 S350P)

Allowed

Number of

S350A or

S350C

Modules

(with

2 S350P)

Allowed

S350C Slave Stage Modules

S350C Slave Stage Modules receive power and
sensor input from the A350 control. S350C Slave
Stage Modules perform switching functions based
upon the A350’s sensor information. (Setpoint and
differential are selected independently at the S350C.)

For more information on these modules, refer to the

System 350
Module Product/Technical Bulletin (LIT-930084).

TM

S350C Temperature Slave Stage

S350P Proportional Stage Modules

S350P Proportional Stage Modules receive power,
setpoint, and sensor input from the A350 control.
The S350P responds with an analog 0-10 VDC and
0-20 mA output signal. This is based upon the A350’s
setpoint and sensor information, with the offset,
throttling range, and minimum output selected at the
S350P.

For more information on these modules, refer to the

System 350
Temperature Stage Module Product/Technical Bulletin
(LIT-930086).

TM

S350P Proportional Plus Integral

D350 Temperature Sensor/Setpoint Display Module

S350A On-Off Stage Modules

S350A On-Off Stage Modules receive power, setpoint,
and sensor input from the A350 control. S350A Stage
Modules perform switching functions based upon the
A350’s setpoint and sensor information, with the offset
and differential selected at the S350A.

For more information on these modules, refer to the

System 350 S350 Temperature, S351 Humidity, and
S352 Pressure On/Off Stage Modules
Product/Technical Bulletin (LIT-930080).

The D350 receives power, sensor, and setpoint
information from the A350. A 3-digit Liquid Crystal
Diode (LCD) gives continuous read-out of the sensed
temperature. Pushing the PRESS FOR SETPOINT
button on the front of the D350 causes the setpoint of
the adjoining A350 to be displayed.

Y350R Power Module

The Y350R provides a convenient method of powering
System 350 modules from a 120 or 240 VAC power
source. The Y350R supplies power to the modules.
See Figure 5 for a typical wiring diagram where a
Y350R is used to power the A350.

For more information on this module, refer to

System 350
Product/Technical Bulletin (LIT-930090)

TM

Y350R Power Module

.

System 350 A350A/B Electronic Temperature Control Product/Technical Bulletin

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