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When using a Dehumidistat or Interface Relay to initiate high speed blower operation on a
furnace, certain thermostats will initiate the outdoor cooling condenser when R and G are closed.
Use this wiring configuration to stop the Dehumidistat from initializing the condenser unit. This
problem can occur at the thermostat because the Y terminal is connected to the G terminal
internal to the stat. When R and G are closed at the furnace (by dehumidistat or relay) 24 Volts
is sent to G at thermostat. 24 Volts is then sent through Y which will initiate outdoor condenser.
The relay will isolate this problem.
NOTE:
This problem does not occur with all thermostats, therefore it is important to fully
commission the installation to determine if this relay configuration is required.
30
R
GWYC
R
GWY
Furnace
T-stat
COM
or Dehumidistat
24 Volt
Relay
NO
Interface Relay
NC
TB-102
1099
Optional Dehumidistat
An optional dehumidistat can be connected to the furnace to help eliminate
excessive moisture during the heating season. When the dehumidistat
senses moisture in excess of the control setpoint, the blower will be
overridden into high speed. This will increase the
ventilation airflow and
create a dehumidification affect. Typical settings are between 30-40 during
the winter and OFF for all other seasons
.
The dehumidistat will connect to R&G terminals on the furnace.
Note: Do not use dehumidistat for hot southern climates.
Dehumidistat
Setting Relative to
Outside Conditions
WINTER:
Set dehumidistat
between 30% to 40%.
If home is too dry,
adjust to higher setting.
If home is too humid,
adjust to lower setting.
SUMMER:
Set dehumidistat
to OFF.
Part # 99-130W