47
Three phase voltage imbalance will cause
motor overheating and premature failure.
The maximum allowable imbalance is 2%.
Voltage imbalance is defined as 100 times the
maximum deviation from the average voltage
divided by the average voltage.
Example:
(221V+230V+227V)/3 = 226V, then
100*(226V-221V)/226V = 2.2%, which
exceeds the allowable imbalance.
Check voltage imbalance at the unit
disconnect switch and at the compressor
terminal. Contact your local power company
for line voltage corrections.
Installing contractor must check for proper
motor rotation and check blower motor
amperage listed on the motor nameplate is
not exceeded. Motor overload protection may
be a function of the variable frequency drive
and must not be bypassed.
Wire control signals to the unit’s low voltage
terminal block located in the controls
compartment.
Variable Speed Compressors
Variable speed compressors with VFD speed
control are available on 7-13, 15, 16, 20, 25,
30, 55, 65 and 75-140 ton units. Variable
speed compressors must not be operated
outside the factory determined turndown
ratio or frequency range. The factory
determined compressor VFD ranges are
given in the following tables.
Table 7 - RN-A through C Cabinet Variable
Speed Compressor Turndown Ratio
Rotation must be checked on all
MOTORS AND COMPRESSORS of
three phase units. Supply fan, exhaust
fan, return fan, and condenser fan
motors must all be checked by a
qualified service technician at startup
and any wiring alteration must only be
Scroll compressors are directional
and will be damaged by operation in
the wrong direction. Low pressure
switches on compressors have been
disconnected after factory testing.
Rotation must be checked by a
qualified service technician at startup
using suction and discharge pressure
gauges and any wiring alteration must
only be made at the unit power
connection.
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