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—13—
B. Differential Enthalpy Control
NOTE: The accessory outdoor-air enthalpy sensor must be
installed BEFORE the economizer hoods are installed on the
unit or hoods will have to be removed.
1. Remove and discard the factory-installed jumper
assembly containing the 800-ohm resistor on the
economizer control module (between terminals S
R
and +). See Fig. 18.
2. Disconnect black wire from economizer control mod-
ule terminal S
O
and blue wire from the OAT (outdoor-
air thermostat).
3. Remove OAT and black wire assembly containing the
620-ohm resistor from the outside of the economizer
(see Fig. 17).
4. Mount the outdoor-air enthalpy sensor (first sensor)
to the economizer on the outside of the unit (in the
same location from which the OAT was removed)
using the 2 screws provided. See Fig. 17.
5. Reconnect the blue wire removed in Step 2 to the
enthalpy sensor terminal +.
6. Cut the violet wire provided to desired length and
terminate with quick-connect terminal provided.
Route the violet wire from the enthalpy sensor termi-
nal S, through the snap bushing, and to the econo-
mizer control module terminal S
O
.
7. Mount the second enthalpy sensor in the return-air
duct (return-air sensor).
8. Route the blue wire (provided) from terminal + on the
return-air enthalpy sensor to the economizer control
module terminal +.
9. Route the violet wire (provided) from terminal S on
the return-air enthalpy sensor to the economizer con-
trol module terminal S
R
.
10. Turn changeover set point dial clockwise past the “D”
setting, or the control will not operate on a differen-
tial. See Fig. 18.
11. Reinstall economizer hood if removed.
IMPORTANT: Be sure all seal strips and RTV sealant are
intact. A watertight seal to inside of unit must be
maintained.
XI. STEP 11 — INSTALL ALL ACCESSORIES
After all the factory-installed options have been adjusted,
install all field-installed accessories. Refer to the accessory
installation instructions included with each accessory.
A. Motormaster® I Control Installation (581A155 and 180
Only)
Install Field-Fabricated Wind Baffles
Wind baffles must be field-fabricated for all units to ensure
proper cooling cycle operation at low ambient temperatures.
See Fig. 25 for baffle details. Use 20-gage, galvanized sheet
metal, or similar corrosion-resistant metal for baffles. Use
field-supplied screws to attach baffles to unit. Screws should
be
1
/
4
-in. diameter and
5
/
8
-in. long. Drill required screw holes
for mounting baffles.
Install Motormaster I Controls
Only one Motormaster I control is required per unit. The
Motormaster I control must be used in conjunction with the
Accessory 0° F Low Ambient Kit (purchased separately). The
Motormaster I device controls outdoor fan no. 1 while out-
door fans no. 2 and 3 are sequenced off by the Accessory 0° F
Low Ambient Kit.
Accessory 0° F Low Ambient Kit — Install the Accessory 0° F
Low Ambient Kit per instruction supplied with accessory.
CAUTION: To avoid damage to the refrigerant coils
and electrical components, use recommended screw
sizes only. Use care when drilling holes.
Fig. 24 — Psychrometric Chart for Solid-State
Enthalpy Control
RH —
Relative Humidity
NOTE:
Dimensions in ( ) are in mm.
Fig. 25 — Wind Baffle Details
CONTROL
CURVE
CONTROL
POINT
(Approx Deg)
AT 50% RH
A
B
C
D
73
68
63
58