Lennox Harmony III Installation Instructions Manual page 17

2. Fan On / Auto Mode Zone thermostats can send a
continuous fan signal to the zone control system. The
zone control system will signal the blower to supply air
to zones calling for continuous fan while no other con-
ditioning calls exist. When the zone control system re-
ceives a conditioning call while satisfying a demand for
continuous fan, it signals the damper controlling the
continuous-fan zone to close. After the conditioning
demand is satisfied, the continuous-fan zone damper
is signaled to reopen.
3. Service Light (Heat pump only) The service light in
the central control thermostat is connected to the out-
door unit. The light illuminates when the outdoor com-
pressor needs to be serviced. The service lights in the
remaining zone thermostats are not connected.
4. Emergency Heat (Heat pump only) The emergency
heat switch prevents the outdoor compressor unit from
responding to a thermostat heating demand. The in-
door unit (furnace or strip heat) supplies all of the heat.
The emergency heat switch light illuminates when the
switch is engaged, and the auxiliary source is used to
satisfy the heating demand in all zones.
Balance Point Setting
(Dual Fuel Systems) Balance Point Sensor (56A83) com-
municates with the Zone Control Board whether or not to
force the Gas Furnace to satisfy heating demands, based
on a comparison of the Balance Point setting with the out-
door temperature.
Zone Mode
The zone control mode (Vacation switch OFF) utilizes the
zone control system's full potential. While in this mode, the
zone control system will respond to demands from any
zone, controlling dampers and regulating blower CFM to
maintain comfort. When the system is in zone mode, the
zone control system responds to demands from any zone
thermostat. (Switch settings are shown in figures 19
through 21.)
The only OPEN supply-air dampers are those zones from
which a demand was received; all other dampers are
CLOSED. The blower operates at a speed based on the
position of the Zone PIAB selection jumpers (and the heat-
ing air reduction jumper, if a call for heat is present).
NOTE − To ensure that the zone control performs optimally,
avoid mixing air between the zones.
Central (Vacation) Mode
When in central mode (Vacation switch ON), the system
responds only to heating or cooling demands from the
master (Zone 1) thermostat); all zones will receive condi-
tioned air. All dampers remain open and the blower oper-
ates at full speed (minus the amount selected by the heat-
ing air reduction jumper). (Switch settings are shown in
figures 19 through 21.)
In Fan−Auto mode, the blower will cycle on and off with
each demand. During gas or electric-strip heating, the
blower may continue after the end of a demand until the
heater is cooled sufficiently.
Cooling Operation
When the Harmony IIIt zone control system receives a
thermostat cooling call, the following events occurs:
S
The zone control unit checks to make sure it has been
at least 5 minutes since the last cooling call ended to
prevent starting against high head pressures.
S
When timed−off delay is satisfied, the zone control unit
starts the outdoor unit with first−stage compressor and
slowly increases the indoor blower speed to achieve
proper CFM. Four minutes must elapse at this state to
allow the system to reach steady−state operation be-
fore staging again.
S
The zone control unit checks the discharge air sensor
for proper temperature. If measured temperature is
7ºF or more above the cooling staging jumper setting,
then Y2 energizes (if available). If both stages of cool-
ing are energized and 4 minutes has elapsed since the
last staging event, and the discharge air sensor (DAS)
detects a temperature less than the cooling staging
jumper, then Y2 is staged off.
S
If, at any time, the discharge air sensor measures a
temperature of 45ºF or below, the zone control unit de−
energizes the Y1 and/or Y2 output, stopping the com-
pressor and preventing the indoor coil from freezing
up. The compressor will not be energized again until
the temperature at the DAS rises by 10ºF and the
timed−off delay expires. During this time, continuous
fan is supplied to the zones calling for cooling.
Heating Operation
Gas furnace In this system, when the zone control re-
ceives a thermostat heating demand, the following events
occurs:
S
The zone control unit sends a W1 signal to the furnace,
which goes through its normal ignition sequence, ex-
cept that while the temperature at the DAS is below
100ºF, the zone control instructs the blower to run at
minimum speed.
S
After the temperature at the DAS rises above 100ºF,
the zone control unit slowly increases the CFM deliv-
ered until it reaches the correct setting. During a call
for heat, the zone control stages the furnace up and
down to maintain the discharge air temperature be-
tween the heating staging jumper setting and 20ºF
above this jumper setting. There is a minimum 3 min-
ute delay between staging events.
Heat Pump with Electric Heat In this system, when the
zone control receives a thermostat heating call, the follow-
ing events occurs:
S
The zone control unit starts the heat pump on first
stage.
S
If after 4 minutes, the temperature at the DAS is not
within the proper range (heating staging jumper setting
and heating staging jumper setting +20) the unit
stages up or down, accordingly.
S
If the air temperature cannot be maintained using the
heat pump alone, the zone control starts the electric
heating stages. Should the discharge temperature ex-
ceed 135ºF, the compressor (and any electric heat that
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HARMONY IIIT SERIES