Johnson Controls System 350 A350A Technical Bulletin page 7

2. Check temperature sensor for proper resistance.
a. Take an accurate, independent temperature
reading at the sensor location.
b. Disconnect the sensor from the control. Using
an ohmmeter, measure the resistance across
the two sensor leads. Consult Figure 7 to verify
sensor conformance.
Temperature
°F
260
240
220
200
180
160
140
120
100
80
60
40
20
0
-20
-40
500 700 900 1100
Resistance (Ohms)
Figure 7: Temperature vs. Resistance
Chart for the A99B Series Sensor
c. If the resistance varies substantially from the
optimal resistance for that temperature, the
sensor or wiring must be replaced.
Note: The sensor reading indicated by the D350 may
differ from thermometer readings due to sensor
tolerances, time constants, accuracy of
thermometer, and other factors.
O
rdering
Table 5: System 350 Products
Item
A350 Temperature Controls
(With Temperature Sensors)
A350 Controls Without
Sensors
Digital Temperature Setpoint
Display Modules
On/Off Stage Modules
Slave Stage Modules
Proportional Stage Modules S350PQ-1C
Power Module
°C
120
100
80
60
40
20
0
-20
-40
1300 1500 1700 1900 2100
Product Code Description
Number
A350AA-1C Range: -30 to 130°F; Adjustable Differential: 1 to 30F°
A350AA-2C Range: 90 to 250°F; Adjustable Differential: 1 to 30F°
A350AA-3C Range: -30 to 130°F; Adjustable Differential: 1 to 30F° (concealed setpoint)
A350BA-1C Range: -35 to 55°C; Adjustable Differential: 0.5 to 17C°
A350BA-2C Range: 30 to 120°C; Adjustable Differential: 0.5 to 17C°
A350AB-5C Range: 90 to 150°F; Adjustable Differential: 1 to 30F°
A350AB-1C Range: -30 to 130°F; Adjustable Differential: 1 to 30F°
A350AB-2C Range: 90 to 250°F; Adjustable Differential: 1 to 30F°
A350BB-1C Range: -30 to 130°F; Adjustable Differential: 1 to 30F°
D350AA-1C Fahrenheit Scale
D350BA-1C Celsius Scale
S350AA-1C Fahrenheit Scale
S350AB-1C Celsius Scale
S350CC-1C Dual Scale (°F and °C)
Dual Scale (°F and °C)
Y350R-1C 120/240 VAC, 50/60 Hz Input; Rectified Class 2, 24 VAC Output
System 350 A350A/B Electronic Temperature Control Product/Technical Bulletin
3. Check the A350 for proper operation.
Note: Steps 1 and 2 must be performed first.
a. Adjust the setpoint dial to at least 40°F (22°C)
below the sensor temperature determined in
Step 2.
b. Increase setpoint by slowly turning the dial until
the control relay and LED turn On and Off.
c. If the relay does not perform as indicated in
Table 4, replace the A350.
Table 4: A350 Relay Troubleshooting
N.O. Contact
Action LED
Heating
On Closed
Heating
Off Open
Cooling
On Closed
Cooling
Off Open
*(T s ) is sensed temperature, and (Sp) is setpoint
temperature.
R
epairs and Replacement
Do not make field repairs or perform calibration.
Replacement controls and A99B Temperature Sensors
are available through the nearest Johnson Controls
representative. See Tables 5 and 6 for ordering
information.
Setpoint
Status Dial Setting*
(T s ) = Sp - Diff
(T s ) = Sp
(T s ) = Sp + Diff
(T s ) = Sp
7