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HARMONY III
T
SERIES
System Components
Zone Control System
The Harmony III
t
zone control system monitors electrical
signals and directs control signals between thermostats,
dampers, and HVAC equipment (see figure 1).
JUMPERS:
STAGING
TEMP‘
HEATING−−
COOLING−−
AIR
REDUCTION
CONT.−−
HEATING−−
Figure 1
EQUIPMENT
CONNECTIONS
THERMOSTAT
CONNECTIONS
24VAC
CONNECTIONS
PIAB
JUMPERS
SYS Config & E−HEAT JUMPERS
DIAGNOSTIC
LEDS
time
delay
override
FAULT
RECALL
BALANCE POINT
SENSOR
CONNECTIONS
PRESSURE
SWITCH CON-
NECTIONS
DISCHARGE
AIR SENSOR
CONNECTIONS
DAMPER
CONNEC
TIONS
FUSES
SYSTEM OPERATION LEDS
Harmony III
t
Zone Control Board
Discharge Air Sensor
A discharge air temperature sensor (88K38) monitors the
supply air. This electronic sensor’s probe (see figure 2) is
inserted into the discharge air plenum to gather air temper-
ature data for the zone control board.
Discharge Air Sensor (Probe)
Figure 2
Separately-Ordered System Components
Thermostats
For all zones, use thermostats that are of this type:
S
electronic thermostat
S
single-stage
S
non-heat pump
S
non-power robbing
S
autochangeover or non−autochangeover
Lennox recommends that zone 1 thermostat [central
(vacation) mode controller] be programmable. Each ther-
mostat must have a dead band between HEAT and COOL.
IMPORTANT
Use only Electronic thermostats. Mechanical or
electro-mechanical thermostats will not work with
the Harmony III
t
zone control system.
Recommended thermostats include:
S
SignatureStat
t
Thermostat − 1 heat / 1 cool (81M26)
[IMPORTANT!
When using this thermostat, only Pre-
cision Mode dehumidification can be used wherein
2°F of over-cooling is allowed. Also, it cannot reduce
the blower speed because the zone control DS con-
trols the blower. Thermostat D terminal is not used.
S
Elite
®
Touch Screen Thermostat − 1 heat / 1 cool /
7−day programmable (X4146).
Transformer
The dampers, zone control board, and zone thermostats
are powered by a single, field−provided 24VAC transform-
er. Together, the zone control panel and thermostats re-
quire 10VA; dampers require 10VA each. The transformer
must have an adequate VA rating to serve all components
(see recommendations in table 1).
Table 1
24VAC Transformer Selection Chart
Catalog
No.
Size
Description
VA LOAD =
Panel plus−
10P17
40VA
120/208/240VAC, 24VAC
3 dampers
10P87
50VA
120/208/240VAC, 24VAC
4 dampers
12P61
75VA
120/208/240VAC, 24VAC
6 dampers
83P74
_
Electrical Box (4-in.
square)
Dampers
Motorized 24VAC powered closed/spring return open
dampers are standard for the Harmony III
t
zone control
system. However, power-open/spring-close" and power-
open/power-close" dampers can be accommodated.
Pressure Switch
A pressure switch [R−22 (21J18); R−410A (51M08)] is re-
quired for applications with a Lennox heat pump (Options 2
and 3). The pressure switch acts as a guard in case of high
head pressures during first− and second−stage heating.