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FIGURE 21
POWER EXHAUST FANS
POWER
EXHAUST FANS
ECONOMIZER
P18
E-Power Exhaust Fan
The power exhaust fan (PEF) requires an optional gravity
exhaust damper and economizer and is used in downflow
applications only. See figure 21. The PEF provides exhaust
air pressure relief and also runs when return air dampers
are closed and the supply air blower is operating. See
installation instructions for more detail.
Power Exhaust Setpoint Adjustment
Locate the A6 enthalpy control in the control area. The EXH
SET potentiometer is factory-set at approximately 50% of
the dial range. See figure 22. Power exhaust fans will be en
ergized 30 seconds after dampers are 50% open. Adjust the
EXH SET potentiometer higher (clockwise toward 10V) to
energize fans when dampers are further open. Adjust the
EXH SET potentiometer lower (counterclockwise toward
2V) to energize fans when dampers are further closed.
(Thirty-second delay allows dampers to partially open be
fore exhaust fan starts.)
F-Drain Pan Overflow Switch S149 (optional)
The overflow switch is used to interrupt cooling operation
when excessive condensate collects in the drain pan. The
N.O. overflow switch is controlled by K220 and DL46 re
lays, located in the unit control panel. When the overflow
switch closes, 24VAC power is interrupted and after a five-
second delay unit compressors are de-energized. Once
the condensate level drops below the set level, the switch
will open. After a five-minute delay the compressor will be
energized.
FIGURE 22
A6 ENTHALPY CONTROLLER
A
B
C
D
Open
Min
Pos
Free
Cool
DCV
EXH
EXH
Set
2V
10V
DCV
Max
2V
10V
DCV
Set
2V
10V
ADJUST POWER
EXHAUST FAN
SETPOINT
ENERGIZED WHEN
DAMPER POSITION
IS HIGHER THAN
EXHAUST FAN
SETPOINT
