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SECTION 1 - FIELD CONTROL MODIFICATIONS
OPTIONAL HEAD PRESSURE CONTROL
The chiller provides an analog output to control sys-
tem equipment, to maintain condenser temperature
for head pressure control. The output may be used to
control a converging or diverting valve, pump VSD, or
other suitable equipment.
The 03630 Microboard terminal TB7-1 (4-20mA) to
TB7-3 (RTN) will provide a 4-20mA output in pro-
portion to the command from the microprocessor for
control. The 03630 microboard terminal TB7-2 (0-
10VDC) to TB7-3 (RTN) will provide a 0-10VDC out-
put in proportion to the command from the micropro-
cessor for control (See Figure 21 on page 16).
The load connected to these terminals must meet the
following specification:
• 0-10V - Input resistance should be greater than 1K
ohms.
• 4-20mA - Input resistance must be less than or
equal 500 ohms.
During head pressure control operation in a con-
figuration (where the means used by a particular site
is to throttle the flow through the single condenser
tube bundle in service), the controlled device should
be setup to inhibit throttling below the minimum re-
quired flow rate through the condenser. This is when
the control panel output is at minimum, such that the
flow switch requirement is maintained. Alternately, a
minimum control output setpoint can be programmed
for run and stop states. See the YZ Operation Manual
(Form 161.01-OM1).
4-20mA
0-10VDC
1
TB7 03630 Microboard
FIGURE 21 - OPTIONAL HEAD PRESSURE CON-
TROL OUTPUT
16
RTN
3
LD23519
FORM 161.01-PW2
ISSUE DATE: 7/18/2018
JOHNSON CONTROLS
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