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CONTROL POINT
CONTROL
(Approx Deg F)
CURVE
AT 50% RH
A
73
B
68
C
63
D
58
Fig. 46 — Psychrometric Chart for
Enthalpy Control
NOTES:
1. Switches shown in high enthalpy state. Terminals 2 and 3 close on enthalpy
decrease.
2. When standard economizer is used with accessory differential enthalpy sen-
sor, set enthalpy control to ''D'' setting.
Fig. 47 — Wiring Connections for Solid-State
Enthalpy Sensor (HH57AC077)
KEYPAD AND DISPLAY MODULE (HSIO)
CONFIGURATION
IMPORTANT: The HSIO keypad and display module
is required for initial start-up of these units. All units
are shipped in standby mode, and the HSIO should be
used to change the unit to run mode. Once the unit is
in run mode, the HSIO is not required for normal
operation.
The keypad and display module provides unit function in-
formation at the unit. See Fig. 48. The module consists of a
keypad with 6 function keys, 5 operative keys, 10 numeric
keys (0 through 9), and an alphanumeric 8-character liquid
crystal display (LCD). Key usage is explained in Table 23.
Each function has one or more subfunctions.
The HSIO keypad and display module is installed by con-
necting the power and communication plugs and can be
easily moved from one unit to another. Because of this flex-
ibility, one HSIO can be used for several units.
Unit operation is controlled by the status of the run/
standby mode on the HSIO. To access the mode, press
on the HSIO keypad, and then press
The HSIO will display either STBY YES or STBY NO.
To enable the unit, press
at the STBY YES display. To disable the unit, press
while at the STBY NO display. Clearing an alarm
ENTER
that has stopped unit operation is accomplished by entering
the STBY YES mode.
IMPORTANT: Use the STBY YES mode when ser-
vicing the unit or running the quick test feature.
IMPORTANT: If remote start function is used, place
LOCAL/REMOTE switch in Local (OFF) position when
ever unit is placed in STBY YES.
SET UNIT TYPE — The correct unit type must be set. The
default unit type is VAV. If the unit is being used in a VAV
application, then the unit type does not need to be changed.
Table 23 — HSIO Keypad Key Usage
FUNCTION
KEYS
Status — To display diagnostic codes and
current operating information about the unit.
Quick Test — To check inputs and outputs for
proper operation.
History — To check most recent alarms.
Service — To enter specific unit configuration
information.
Set Point — To enter operating set points and
day/time information.
Schedule — To enter occupied/unoccupied
schedules for unit operation.
OPERATIVE
KEYS
Expand Display — To display a non-
abbreviated expansion of the display.
Clear — To clear the screen and return to previous
display. Also used to enter data value
CLEAR
of zero.
Up Arrow — To return to previous display position.
Down Arrow — To advance to next display position.
To enter data.
ENTER
EXPN
STAT
EDIT
SET
SCHD
Fig. 48 — Keypad and Display Module (HSIO)
36
or
and press
CLEAR
ENTER
USE
USE
TEST
1
2
3
SRVC
ALRM
4
5
6
HIST
ALGO
CLEAR
7
8
9
ENTER
-
0
.
while
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