On the 48DK/50DY units, the inlet guide vane motor dif-
ferential pressure switch is located on the post on the left-
hand side of the blower assembly (when facing the blower
assembly). Access is through the access door labeled FAN
SECTION on the end of the unit (opposite condenser sec-
tion of the unit). See Fig. 27.
SIZE 034,044 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. 28
and 29.
SIZE 054-074 UNITS — The inlet guide vane differential
pressure switch is mounted on an upright located behind the
evaporator-fan motor. See Fig. 29 and 30.
Differential Pressure Switch Set Point and Null
Span (Units Equipped with Inlet Guide Vane and
Static Pressure Control Option) —
See Fig. 26-30
for location of switches in unit. Differential pressure switch
has an adjustable set point range of 1.1 in. wg to 3.5 in. wg.
Factory setting is 1.9 in. wg. To adjust set point, turn set
point adjusting screw (see Fig. 31) clockwise to decrease set
point and counterclockwise to increase set point. This switch
also has an adjustable null span. The null span is the pres-
sure 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 minimum 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 adjust null span, turn null adjusting screw
(Fig. 31) clockwise 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.
*The inlet guide vane differential pressure switch for the 034,044 units
and the modulating power exhaust differential pressure switch
(034-074 units) are located in the back of the unit in the auxiliary
control box. Their locations are not shown in this figure.
Fig. 28 — Inlet Guide Vane Motor, 50DK034-074 Units
*The inlet guide vane differential pressure switch for the 034,044 units
and the modulating power exhaust differential pressure switch
(034-074 units) are located in the back of the unit in the auxiliary
control box. Their locations are not shown in this figure.
Fig. 29 — Inlet Guide Vane Motor,
48DK/50DY034-074 Units
Fig. 30 — Location of Modulating Power Exhaust
Control Box, 024-030 Units
NULL DECREASE
SET POINT
DECREASE
PLANE
SET
POINT
INDICATOR
SET
POINT
ADJUSTMENT
NULL
ADJUSTMENT
COM
N.C.
N.O.
CAPACITOR
COM — Common
NC
— Normally Closed
NO
— Normally Open
Fig. 31 — Differential Pressure Switch for Inlet Guide
Vane and Static Pressure Control Option and
Modulating Power Exhaust Option
22
