GAS FURNACE
Page 31
HARMONY IIIT ZONE CONTROL SYSTEM
VSM Furnace System Operation (G61MPV & G60UHV [cont’d})
Heating Operation
Gas furnaceIn this system, when the zone control re-
ceives a thermostat heating demand, the following events
occur:
S The zone control sends a W1 signal to the furnace, which
goes through its normal ignition sequence, except 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 slowly increases the CFM delivered 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 between the heating staging jumper setting and
20ºF above this jumper setting. There is a minimum 3 minute
delay between staging events.
NOTE − See page 26 for additional notes on operation with
G71MPP & SLP98 furnace.
Heat Pump with Electric HeatIn this system, when the
zone control receives a thermostat heating call, the follow-
ing events occur:
S The zone control starts the heat pump on 1st−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, ac-
cordingly.
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 exceed 135ºF,
the compressor (and any electric heat that may be on) is
turned off and continuous fan runs (if the demand for heat re-
mains) until the air temperature falls below 130ºF and the
minimum timed−off delay expires.
S If the heat pump goes into defrost mode, the zone control en-
ergizes all stages of compressor and the 1st−stage of electric
heat. If the defrost process lasts longer than 20 minutes, the
zone control, presuming a defrost board failure, de−ener-
gizes the heat pump and instructs electric heat to service the
remainder of the current heating call. (The heat pump will be
tried again on the next heating call.)
Dual Fuel−Heat Pump with Gas FurnaceIn this sys-
tem, when it receives a thermostat heating call, the zone
control responds in one of two ways:
1. Outdoor temperature below balance point (bal-
ance point sensor closed, red Balance Point Sensor
LED on): the zone control sends a W1 signal to the fur-
nace to satisfy heat demands, staging the furnace to
maintain discharge air temperatures between 110ºF
and 130ºF.
2. Outdoor temperature above balance point (bal-
ance point sensor open, red Balance Point Sensor
LED off): the heat pump is first used to satisfy the de-
mand. If, after 20 minutes, the heat pump fails to main-
tain the required discharge air temperature, the zone
control will discontinue using the heat pump and initi-
ate furnace heating. (A five−minute delay exists be-
tween stopping the heat pump and starting the fur-
nace.) In this mode, all heating calls for the next three
hours are serviced with the gas furnace. Also, diag-
nostic lights 2, 3, and 4 blink to indicate that the zone
control is operating within this 3−hour furnace lock−in
time. During this time, the zone control stages the fur-
nace to maintain discharge air temperatures between
110ºF and 130ºF. After the 3−hour delay expires, the
heat pump will again be tried on the next heating call.
Defrost Tempering (Optional)
If installed, refer to De-
frost Operation on Page 23 for Defrost Tempering operation.
Emergency heat mode
When the unit is setup for heat pump and the emergency
heat switch is turned on, the unit will satisfy all heating de-
mands with electric backup heat or, in a dual fuel system,
the heat demand is satisfied by the gas furnace.
Humiditrol® mode (Enhanced Dehumidification
Accessory)
When the unit is equipped for dehumidification (Enhanced
Dehumidification Accessory and Humiditrol
®
Zoning Ac-
cessory installed), the unit will satisfy all demands for de-
humidification. Refer to supplemental kit information De-
humidification Interface Kit for Harmony IIIt Zone Control.
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