3. Cool to Dehumidify Mode—This mode tells the system to
operate the compressor, with limits, when there is a dehu-
midify demand and there is no cooling demand. The limits are
that the system may overcool zones by up to 3° F., while
attempting to satisfy a dehumidify demand. Within this 3°F.
range, there is an additional balance between overcooling and
humidity satisfaction. When overcooling must occur, the
dehumidify set point is adjusted upward by 2% for each
degree of zone overcooling. For example, a cooling set point
of 76°F. and a dehumidify set point of 62% is equivalent to a
cooling set point of 75° F. and a humidity set point of 64%.
This balancing of temperature and dehumidification demand
results in smoother operation of the equipment at the set
points. Adjustment of the dehumidify set point as described
above is internal to the system and does not show on the
display.
During cool to dehumidify demand, the compressor runs a
maximum of 10 minutes ON followed by 10 minutes OFF. As
in normal dehumidify, a continuous fan is turned off for 5
minutes at the end of each cooling cycle. Again, to utilize this
feature, the equipment blower off delay must be defeated.
If any of the zones are set to OUT, their dampers will fully
open while the compressor is running and a cool to dehu-
midify demand exists. While the compressor is off or if their
temperature goes below 70°F., their dampers close.
4. Vacation Dehumidify Mode—this is an extension of Cool to
Dehumidify Mode. This mode is initiated when cool to
dehumidify is selected AND all zones are set to OUT. All
zones are conditioned to keep them below 85°F. If the
humidity rises above the dehumidify set point, cooling can
occur to satisfy the dehumidify demand until zones reach 70°.
This selection is ideal for unoccupied homes in high humidity
climates. This mode can be selected — when cool to dehu-
midify is selected — by pressing HOLD, OUT , and ALL
ZONE in that order. Alternatively, each zone can be set to
HOLD and OUT, but this requires more button presses.
Remember, in vacation mode there are no temperature set
points, but a dehumidify set point must be selected. Suggested
values are 60 to 70 percent.
To exit the humidity setup mode, press HOLD/END button once.
If no button is pressed for 3 minutes, Comfort Zone II -B will
automatically save any new settings and then return back to normal
operation.
Additional Dehumidification Comments
Variable Speed Superdehumidification is selected by configuration
Option 7. It can only be implemented with Comfort Heat pump
compatible systems because it require a variable speed indoor unit
with superdehumidify capability. During a cool-to-dehumidify
call, it provides maximum dehumidification by reducing airflow to
its lowest possible value. The actual command from CZII to the
indoor unit is a Y signal without a G signal in addition to a
dehumidify signal. All other characteristics of cool-to-dehumidify
are unchanged.
Dehumidify actions are initiated when humidity rises to 2% above
set point and are terminated when humidity drops to 2% below set
point. This prevents unnecessary toggling of dehumidify actions
when humidity is near the set point.
With any dehumidify selection, if the system has 2-speed com-
pressor (DIP switch 2 is ON) and does not have a variable speed
blower (configuration option 5 is set to OFF), all cooling will be
done at high speed while a dehumidify demand exists. This is
because the combination of a 2-speed compressor without a
variable speed blower generally has poor humidity removal on low
speed.
Dehumidify Output and Equipment Connections
When there is a dehumidify demand, dehumidify output is
activated, which means that a 24vac 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 24vac signal to initiate dehumidification. Equip-
ment has been designed to operate in this manner, so Comfort
Zone must now accommodate the existing equipment.
FK and FV Series Variable-Speed Fan Coils, all 58UHV and
58UXV 80% Variable-Speed Furnaces, and 58MVP 90%
Variable-Speed Furnaces with the DE connection have dehumidify
inputs which connect directly to Comfort Zone DHUM output.
They are compatible with the reverse logic output and will reduce
their cooling CFM by approximately 20% when a dehumidify
demand is present.
The FK and FV Series Fan Coil have a terminal marked DH which
should be connected to the Comfort Zone DHUM output. Jumper
J1 on the 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. 39 through 42.
On 58UHV and 58UXV 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 Comfort
Zone DHUM terminal. See Table 6 and Fig. 23 through 26.
Carrier 58MVP 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 equipment controller and the furnace.
The relay coil is connected between DHUM output on the
equipment controller 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. 27 through 30. 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%.
On newer style variable-speed furnace controls, a field-supplied
relay IS NOT required. The DHUM output on the equipment
controller 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
Table 2—Displays of Available Dehumidify Modes
SELECTION
MODE DISPLAY
DEHUMIDIFY SET POINT
Dehumidify Off
Blank
OF
Normal Dehumidify
Blank
Dehum Set Point
Cool to Dehumidify
COOL
Dehum Set Point
15
