JOHNSON CONTROLS
167
SECTION 8 – SERVICE
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
8
Discharge Pressure Transducer
The discharge Pressure Transducer is located in the
common discharge line of the tandem compressors for
each refrigerant circuit. The purpose of this transducer
is to sense and convert the discharge pressure into a DC
voltage. The DC voltage is then sent to the IPU board
where it is used to control the number of condenser fan
when the unit is in cooling operation. The discharge
pressure value, in PSIG, is displayed by the User In-
terface.
The Discharge Transducer has a range of 0 to 500
PSIG, with a linear output of 0 to 5VDC.
illustrates the DC volt output from the trans-
ducer for a given discharge pressure.
Suction Pressure Transducer
The optional suction pressure transducer is located in
the common suction line of the tandem compressors for
each refrigerant circuit. The purpose of the transducer
is to sense and convert the suction pressure to a DC
voltage. The DC voltage is then sent to the IPU board
where it is displayed by the User Interface. When this
option is installed the IPU board will also calculate and
display the Evaporator Superheat value for the system.
The Suction Transducer has a range of 0 to 200 PSIG,
with a linear output of 0 to 5VDC.
illustrates the DC volt output from the transducer
for a given suction pressure.
TABLE 59 -
PRESSURE TRANSDUCERS
SUCTION
TRANSDUCER
DISCHARGE
TRANSDUCER
PRESSURE
PSIG
VOLTAGE
VDC
PRESSURE
PSIG
VOLTAGE
VDC
0
0.50
0
0.50
25
1.00
50
1.00
50
1.50
100
1.50
75
2.00
150
2.00
100
2.50
200
2.50
125
3.00
250
3.00
150
3.50
300
3.50
175
4.00
350
4.00
200
4.50
400
4.50
Humidity Sensors
The humidity sensor outputs a 0 to 5VDC in response to
the relative humidity sensed. An outdoor air humidity
sensor is used whenever the economizer is configured
for single or dual enthalpy. A return air humidity sensor
is used whenever the economizer is configured for dual
enthalpy. A humidity sensor is also used to monitor the
humidity in the space between the slab and raised floor
system used for FlexSys applications.
gives the relationship between the voltage output
of the humidity sensor and the % relative humidity.
CO
2
Sensor
Two CO
2
sensors are used in conjunction with the de-
mand ventilation option. In demand ventilation the IPU
board monitors the CO
2
level of the outdoor air and the
CO
2
level in the conditioned space and varies the amount
of ventilation air based on the relationship between these
gives the volts DC
output for a given CO
2
level.
Furnace Status Input
The IPU board monitors the operation of the Staged
and Modulating Gas Heat sections and displays the sta-
tus through the STATUS screen of the User Interface.
The operation of each of the gas heat sections is moni-
tored by a multiplexer installed in the gas heat section.
When a gas heat section is energized, it sends a 24-volt
signal to the multiplexer. The multiplexer takes the five
ON/OFF inputs and converts them into a 0 to 5VDC
signal that is sent to the IPU board. The IPU board then
decodes this analog input and displays the furnace sec-
tion status.
Table 62 on page 168 and Table 63 on
show the relationship between the DC volt-
age and the furnace operation status.
TABLE 60 -
HUMIDITY SENSOR OUTPUTS
%
RELATIVE
HUMIDITY
OUTPUT
VOLTAGE
VDC
%
RELATIVE
HUMIDITY
OUTPUT
VOLTAGE
VDC
5
0.25
55
2.75
10
0.50
60
3.00
15
0.75
65
3.25
20
1.00
70
3.50
25
1.25
75
3.75
30
1.50
80
4.00
35
1.75
85
4.25
40
2.00
90
4.50
45
2.25
95
4.75
50
2.50
100
5.00