3. Dehumidify Off
Dehumidification can be turned off completely. This can be
done without changing existing set points.
TO SELECT DEHUMIDIFICATION (BETWEEN NORMAL,
COOL TO, AND OFF)
Press HUMIDITY button to bring up humidity selections. Succes-
sive presses will show "hu" or "dhu" in clock display. Select "dhu"
for dehumidify selections. The large display shows actual humidity
level. The smaller display (in cool set point location) shows
dehumidify set point (DSP) or OF (off). When DSP value is
displayed, its value can be changed with up and down buttons.
Successive presses of MODE button moves between 3 choices
above and each will be indicated as in Table 5.
SUPERDEHUMIDIFY (WITH COOL TO DEHUMIDIFY)
This selection only affects cool-to-dehumidify operation. It is part
of the installer setup (see Configuration Option No. 7) and must be
made by installer. The Homeowner’s Guide does not cover this
selection. A requirement is the use of a variable-speed indoor unit
with superdehumidify capability. During cool-to-dehumidify call,
it provides maximum dehumidification by reducing airflow to a
minimum. The actual superdehumidify command from Thermidis-
tat Control to the indoor unit is a Y signal without a G signal in
addition to dehumidify signal. The indoor unit responds to this
combination by reducing the airflow to a minimum. All other
characteristics of cool to dehumidify are the same.
ADDITIONAL DEHUMIDIFY COMMENTS
Dehumidification can be enhanced (with some efficiency loss) by
turning blower off immediately at the end of each cooling cycle
(eliminating normal 90 sec blower off delay). Where maximum
humidity removal is desired, this should be done, if possible. Fan
coils have the capability of removing this off delay, furnaces do
not. On FK Fan Coils, set delay tap to 0/0. On standard fan coils,
a jumper can be cut to disable off delay. Refer to fan coil
Installation Instructions for details. If FAN is set for continuous
operation (fan ON icon displayed), G output is turned off for 5
minutes at the end of each cooling cycle as long as dehumidify
demand exists.
Like humidify, dehumidify actions are initiated when humidity is
2 percent above set point and are terminated when humidity drops
to 2 percent below set point. This prevents unnecessary toggling of
dehumidify actions when humidity is near set point.
The vacation mode contains additional dehumidify features de-
signed to protect an unoccupied home. Refer to the "Vacation"
section for additional information.
With any dehumidify selection, if the system has a 2-speed
compressor (DIP switch No. 2 is ON) and does NOT have a
variable-speed blower (Configuration Option No. 5 set to OFF), all
cooling will be done at high speed while dehumidify demand
exists. This is because the combination of 2-speed compressor
without variable-speed blower generally has poor water removal
on low speed.
DEHUMIDIFY OUTPUT AND EQUIPMENT CONNECTIONS
When there is a dehumidify demand, dehumidify output is
activated, which means that a 24-vac signal is removed from the
DHUM output terminal. In other words, dehumidify output logic is
reversed — output is turned ON when no dehumidify demand
exists and is turned OFF when demand exists. This logic reversal
has come about from historical use of a standard humidistat to do
dehumidification. The humidistat contacts open on high humidity,
thus removing a 24-vac signal to initiate dehumidification. Equip-
ment has been designed to operate in this manner, so the
Thermidistat Control must now accommodate the existing equip-
ment.
Bryant FK Series Variable-Speed Fan Coils, all 333BAV and
333JAV 80% Variable-Speed Furnaces, and 355MAV 90%
Variable-Speed Furnaces with the DE connection have dehumidify
inputs which connect directly to Thermidistat Control DHUM
output. They are compatible with the reverse logic output and will
reduce their cooling CFM by approximately 20 percent when a
dehumidify demand is present.
The FK Series Fan Coil has a terminal marked DH which should
be connected to the Thermidistat Control DHUM output. Jumper
J1 on fan coil MUST be removed. It is located behind the DH
terminal. Additionally blower delay tap on fan coil should be set to
0/0 (no ON delay and no OFF delay) when using cool to
dehumidify. With this selection, the blower stops when G signal is
removed, preventing re-evaporation of water from the coil which
would occur during the normal 90 sec blower off delay. See Table
6 and Fig. 7 through 10.
On 333BAV and 333JAV Furnaces, a green wire marked DHUM
is connected to a spade lug which is connected to the G input
terminal. Unplug spade lug, cut off spade receptacle from wire
end, and splice a wire between green DEHUM wire and Thermi-
distat Control DHUM terminal. See Table 6 and Fig. 19 through
22.
Bryant 355MAV Furnaces also have a DEHUM input. The
DEHUM input acts differently depending on which style of
variable-speed furnace control you have. The older style variable-
speed furnace control DOES NOT have a DE connection while the
newer style variable-speed furnace control has a DE connection.
Both of these variable-speed furnace controls function the same
except the DEHUM logic is reversed.
On the older style variable-speed furnace controls, a field-supplied
relay is required between the Thermidistat Control and furnace.
The relay coil is connected between DHUM output on the
Thermidistat Control and COM terminal on the furnace control. Its
normally closed contact is connected between R and DEHUM
terminals on the furnace control, where the DEHUM terminal is a
spade lug located next to the transformer secondary connections.
See Table 6 and Fig. 23 through 26. When a dehumidify demand
exists, relay is de-energized, and normally closed contacts supply
24vac to the furnace DEHUM terminal. As a result the furnace
control reduces the blower airflow by 15 percent.
On newer style variable-speed furnace controls, a field-supplied
relay IS NOT required. The DHUM output on the Thermidistat
Control is instead connected directly to the DEHUM terminal on
the furnace control, where the DEHUM terminal is a spade lug
located next to the transformer secondary connections. In addition
the DE jumper located next to the DEHUM terminal must be
removed to enable the DEHUM input. See Table 6 and Fig. 27
through 30. When a dehumidify demand exists the furnace control
reduces the blower airflow by 21 percent.
C.
Vacation
A vacation selection is available specifically for times where the
home will not be occupied for an extended period. For conve-
nience, 1 button selects vacation mode which is indicated by OUT
icon on display. Vacation mode also has an automatic hold,
TABLE 5—DEHUMIDIFICATION SELECTIONS
SELECTION
MODE DISPLAY
FAN DISPLAY
DEHUMIDIFY SP
DISPLAY
Normal Dehumidify
Blank
Blank
DSP Value
Cool to Dehumidify
COOL
Blank
DSP Value
Dehumidify OFF
Blank
Blank
OF
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