JOHNSON CONTROLS
167
SECTION 8 – UNIT OPERATION
FORM 150.67-NM2
ISSUE DATE: 01/31/2019
8
PROGRAMMING YCAL0019-0028
Condenser fan control type must be programmed un-
der both the OPTIONS and PROGRAM keys when a
VFD is installed on the chiller. Under the OPTIONS
key, FAN CONTROL must be programmed for DIS-
CHARGE PRESSURE CONTROL only. This will as-
sure condenser fan control of the chiller is solely by
discharge pressure, with no ambient control.
Under the PROGRAM Key, the FAN CONTROL
ON PRESSURE should be programmed for 385
PSIG and the FAN DIFFERENTIAL OFF PRES-
SURE must be programmed for 125 PSIG.
Programming as suggested assures the chiller control
points for the second fan in the fan staging sequence
and the inverter control points are matched for opti-
mum control of the fans at reduced ambient tempera-
tures, assuring superheat and oil control is not compro-
mised. When the chiller and VFD fan control points are
programmed properly, the fans will operate as outlined
in Table 26 on page 167.
TABLE 26 - YCAL0019 – 0028 VFD LOW AMBIENT OPTION – CONDENSER FAN CONTROL OPERATION
FAN STAGE ON OFF
CONTACTOR MICROBOARD FAN #
SYS 1 SYS 1 SYS 1
1:
VFD Control
(1 fan
Variable Speed)
Fan Speed Is A Function
Of Liquid Temperature
Fan will turn on when
liquid line temperature is
above 65º F.
Speed increases with
temperature
FAN Will Turn OFF When
Liquid Temperature Drops
Below 65 °F
7M TB7-3 1
2:
1 Fan VFD
Control
2nd Fan Full
Speed Under
Contactor Control
385 PSIG, Both Fans
Will Be Running Full
Speed
Discharge Pressure
< 260 PSIG (Pressure Is
< Fan Control ON Pressure
of 385 PSIG Minus Fan
Differential
Pressure of 125 PSIG =
260 PSIG) Fan 1 Will Still
Be Running
7M & 8M
TB7- 3
&
TB7-10
1 & 3
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