Table of Contents
Advertisement
High current conditions may result from power problems,
contactor problems, wiring problems, refrigerant over-
charge, very high chilled liquid temperatures, very high
ambients, or situations that cause high discharge pres-
sures.
The micro begins monitoring "average" motor current af-
ter 5 seconds of compressor operation on chillers with
ACROSS-THE-LINE start and after 20 seconds on chill-
ers with WYE-DELTA starters. Between 5 - 7 seconds of
run time (ACROSS-THE-LINE) or 20 - 22 seconds (WYE-
DELTA) "average" motor current must be less than 120%
FLA, or the micro will shut the compressor down. After 7
seconds of operation (ACROSS-THE-LINE) or 22 sec-
onds (WYE-DELTA), "average" motor current must be less
than 115% FLA as long as the compressor continues to
run. Anytime these current thresholds are exceeded for
3 seconds, the system will shut down.
NOTE: Do not confuse FLA and RLA. FLA (full load
amps) is approximately 1.2 x RLA. RLA (running
load amps) specified on the motor / chiller name-
plate is typical current demand under rated op-
erating conditions in a fully loaded system. There-
fore, do not expect to always see 100% FLA
when the system is fully loaded. In a fully loaded
condition, motor currents may often run 65 - 85%
FLA.
An example of the high current fault display message is
shown below:
S Y S
1
H I G H
S Y S
2
H I G H
Phase Rotation Safety
The Phase Rotation Safety assures that the compressor
rotates in the proper direction eliminating the possibility
of damage to the compressor.
The micro will shut the compressor down after 4 sec-
onds of operation whenever the phasing of the incoming
power wiring is incorrect. Anytime this fault occurs, the
solution is to switch any two of the three incoming power
wires.
An example of the Phase Rotation Fault message is
shown below:
S Y S
1
P H A S E
S Y S
2
P H A S E
High Discharge Temperature Safety
This safety assures that the compressor's screws do
not overheat and expand causing them to be damaged.
108
M T R
C U R R
M T R
C U R R
R O T A T I O N
R O T A T I O N
The compressor will not start or will shut down in the first
5 seconds of operation if the discharge temperature ex-
ceeds 225°F.
After 5 seconds of operation, a warning message will be
displayed if discharge temperature exceeds 225°F. The
compressor will shut down if the discharge temperature
exceeds 230°F.
This safety operates in conjunction with the Oil Pressure
Safety to assure proper oiling is taking place. If oiling is
lost for any reason, the oil seal between the two screws
will be lost and the compression ratio will drop. The loss
in compression ratio will cause the discharge tempera-
ture to rise.
An example of the High Discharge Temperature warning
and fault message is shown below:
S Y S
1
H I G H
S Y S
2
H I G H
Low Motor Current Safety
This safety protects against system problems that cause
low motor current, motor overheating, high motor current
(overload) and high discharge pressure. These problems
could result in motor failure, compressor failure, and sys-
tem malfunction.
Shown below is the display relating to this safety. Actual
current as well as MP (Motor Protector) and HP (High
Pressure Cut-out) are related to this safety. A Motor Over-
load Relay (OL) will also cause a low current fault.
S Y S
1
L O W
S Y S
2
L O W
Low "average" motor current may result from running with
low or no refrigerant. This safety protects against gross
refrigerant problems until the low pressure bypass is de-
activated by the micro. Low current may also be due to
contactor or power problems or a compressor that is not
pumping due to a mechanical malfunction. The micro
monitors motor current with 3 C.T.'s per motor, one on
each phase T1, T2 and T3 in both Wye-Delta or Across-
the Line starters.
The micro begins monitoring "average" motor current af-
ter 5 seconds of compressor operation on chillers with
ACROSS-THE-LINE start and after 20 seconds on chill-
ers with WYE-DELTA starters. After 5 seconds of opera-
tion (ACROSS-THE-LINE) or 20 seconds (WYE-DELTA),
"average" motor current must be greater than 5% (ambi-
ent 25°F), 10% (ambient 26 - 45°F), or 15% (ambient
45°F) FLA but less than 115% FLA as long as the com-
pressor continues to run. Anytime these current thresh-
olds are exceeded for 3 seconds, the system will shut
down.
D S C H
T E M P
D S C H
T E M P
C U R R / M P / H P
C U R R / M P / H P
YORK INTERNATIONAL
Advertisement
Table of Contents
