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Supply Fan Control with IGV Option — The inlet
guide vane option will modulate the supply fan airflow in
order to maintain the static pressure in the supply duct. The
set point for duct static pressure is established at the differ-
ential pressure switch for the IGV control.
SIZE 034-048 UNITS — The inlet guide vane differential
pressure switch is located in the auxiliary control box mounted
in the corner under the side air hood that is next to the access
door marked FILTER SECTION. To gain access to this con-
trol box, remove the auxiliary control box cover. When
replacing cover, be sure to properly secure it in order to
prevent water from being drawn into the unit. See Fig. 36
and 37.
SIZE 054-104 UNITS — The inlet guide vane differential
pressure witch is mounted on an upright located behind the
supply-fan motor. See Fig. 36-38.
The IGV differential pressure switch has an adjustable
set point range of 1.1 to 3.5 in. wg. and a factory setting of
1.9 in. wg.
To adjust set point, turn set point adjusting screw (see
Fig. 39) clockwise to decrease set point and counterclock-
wise to increase set point. This switch also has an adjustable
null span. The null span is the pressure change that can be
made without contacts opening or closing. It is adjustable
from 0.06 in. wg to 0.17 in. wg when set point is at mini-
mum position (1.1 in. wg) and 0.11 in. wg to 0.31 in. wg
when set point is at maximum position (3.5 in. wg). To ad-
just null span, turn a null adjusting screw (Fig. 39) clock-
wise to decrease span and counterclockwise to increase span.
All switches leave factory with null span set at maximum
position. The smaller the null span, the closer the pressure
will be maintained to desired set point.
Supply Fan Control with VFD Option — The VFD
option will modulate Supply Fan motor (and thus wheel) speed
to maintain the static pressure in the ductwork. Set point for
the VFD option is set at the VFD, using the display key-
board on the front of the VFD enclosure. See Fig. 40.
NOTE: The VFD will always provide the proper phase
sequence to the supply-fan motor. The supply-fan motor op-
erates in proper rotation regardless of the phase sequence to
the unit. If, upon start-up, the outdoor fans operate back-
wards but the supply fan operates in the correct direction,
reverse any two leads to the main terminal block. All fans
will then operate in the correct direction.
To set the duct static pressure, perform the following steps.
The factory setting is 2.5 in. wg. The duct transducer has
a range from 0 to 5 in. wg. The transducer output is 4 to
20 mA, therefore, 0 to 5 in. wg is proportional to the 4 to
20 mA and must be expressed to the VFD in terms of per-
centage of the frequency range. Refer to Table 13. The set
point value is a percentage of the maximum output fre-
quency. Locate the duct static pressure closest to that de-
sired and use the corresponding set point value. If necessary,
interpolation between duct static pressures is permissible.
Factory-installed optional VFD is located near the sup-
ply fan and motor. During any service work or pro-
gramming at the VFD, operation of the fan and motor
is not desirable and may be dangerous. Either disable
the unit supply fan (following instructions below) or in-
stall the accessory VFD remote display accessory.
*Theinlet guidevane differentialpressure switchfor the034-048units
is located in the back of the unit in the auxiliary control box. Its lo-
cation is not shown in this figure.
Fig. 36 — Inlet Guide Vane Motor,
50FK,JK034-074 Units
*Theinlet guidevane differentialpressure switchfor the034-048units
is located in the back of the unit in the auxiliary control box. Its lo-
cation is not shown in this figure.
Fig. 37 — Inlet Guide Vane Motor, 48FK,JK, 50FY,JY,
and 50FJX,FJY,FKX,FKY034-074 Units
Fig. 38 — Inlet Guide Vane Motor,
Size 078-104 Units
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