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8.4
CONDENSER FAN CONTROL
The chiller is equipped with 6 condenser fans, with 3
fans per system as shown in Fig. 50 below. Fan control is
via Outside Ambient Temperature (OAT) and Discharge
Pressure (DP). There are 3 or 6 stages of fan control,
depending upon the version of EPROM, utilizing 3
outputs per system from the Relay Output Board. The
fan stages will operate according to Tables 3, 4, 5 and
6, according to the EPROM version installed. Operation
of the fans, regardless of the EPROM version, will be
satisfactory in all ambient conditions,
Tables are provided which show fan on/off points and
also include fan contactors, wire numbers, and Relay
Output Board output numbers related to specific fans
operation. System 1 fan contactors are controlled by
Relay Output Board #1 and System 2 fan contactors are
controlled by Relay Output Board #2.
FIG. 50 – CONDENSER FAN CONTROL LAYOUT
FOR DXST COMPRESSORS UNITS
EPROM Versions C.ACS.09.01 (F350)
and C.ACS.09.02 (3902)
Fan operation on these versions is outlined in Table 3.
Condenser fan ON conditions are governed solely by the
Discharge Pressure (DP). When the DP rises above 220
PSIG, fan stage 1 is activated. From there, subsequent
fan stages are activated as the discharge pressure rises
in increments of 15 PSIG, except stage 6, which is acti-
vated when the DP rises over 290 PSIG. The system will
remain at the highest fan stage reached unless the OFF
conditions outlined in the next paragraph are satisfied.
Condenser fan OFF conditions are governed by both the DP
and OAT. Fan staging will be decreased from the highest
fan stage reached if both the DP and OAT requirements
JOHNSON CONTROLS
are met. For example, if a system is at fan stage 4, and the
DP falls below 195 PSIG and the OAT drops below 75 °F,
the fan stage will be reduced to stage 3.
EPROM Version C.A17.09.02 (5320)
Fan operation on these versions is outlined in Table 4.
These EPROM versions operate very similar to versions
0 and 1. The only difference is that the ON/OFF pres-
sures are 15 PSIG lower. Condenser fan ON conditions
are governed solely by the Discharge Pressure (DP).
When the DP rises above 205 PSIG, fan stage 1 is acti-
vated. From there, subsequent fan stages are activated
as the discharge pressure rises in increments of 15 PSIG,
except stage 6, which is activated when the DP rises
over 275 PSIG. The system will remain at the highest
fan stage reached unless the OFF conditions outlined in
the next paragraph are satisfied.
Condenser fan OFF conditions are governed by both the DP
and OAT. Fan staging will be decreased from the highest
fan stage reached if both the DP and OAT requirements
are met. For example, if a system is at fan stage 4, and the
DP falls below 180 PSIG and the OAT drops below 75°+
F, the fan stage will be reduced to stage 3.
EPROM Versions C.A32.09.02 (0483),
C.ACS.09.02 (D87E), and C.A06.09.03 (E10C)
These EPROM's operate according to the Flowchart in
Fig. 51. This control scheme is designed to minimize fan
cycling. Whenever discharge pressure stabilizes between
150 PSIG and 250 PSIG, the micro will neither start or
stop stages of fans.
LD06907
If discharge pressure rises between 250 PSIG and 285
PSIG, the micro will add another fan stage and start a 15
minute timer. If the discharge pressure remains in this
range for 15 minutes, another step of fan cycling will
be added and the micro will restart the 15 minute timer.
If discharge pressure falls between 150 PSIG and 120
PSIG, a step of fan cycling will be dropped and the micro
will start a 15 minute timer. If the discharge pressure
remains in this range for 15 minutes, another step of
fan cycling will be dropped and the micro will restart
the 15 minute.
If discharge pressure rises above 285 PSIG, the micro
will add a step of fan cycling every 5 seconds, until the
discharge pressure drops below 285 PSIG in an effort to
quickly control the discharge pressure to an acceptable
range.
FORM 201.18-NM7
8
167
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