H8908B Humidistat
H8908C Dehumidistat
INSTALLATION INSTRUCTIONS
APPLICATION
OUT
PER
°
F
°
F
°F
+10
°F
DOO
R
ATU
RE
HUM
SET
IDIT
TING
15%
Y
TEM
-20
-10
-30
-25
-20
-10
°
C
°
C
20%
25%
30%
35%
40%
The H8908B Humidistat and H8908C Dehumidistat
(humidity controllers) provide automatic low voltage
control of humidifiers and dehumidifiers or ventilators,
respectively, in central heating and air conditioning sys-
tems. They have a spst, snap-acting, dust-proof switch
and are designed for wall or surface duct mounting.
Humidity Control
Régulateur d'humidité
0
°
C
°
C
+20
20
°F
°
F
-5 °C
0
Ove
r
Ove
r
°
C
INSTALLATION
When Installing this Product...
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a haz-
ardous condition.
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable
for your application.
CASE REMOVAL
SLOT
HOLE FOR WIRING
THE DUCT MOUNTING
INSTALLATIONS
M13371
Fig. 1. H8908B Humidistat.
3. Installer must be a trained, experienced service
technician.
4. After installation is complete, check out product
operation as provided in these instructions.
Wall Mounting
IMPORTANT
Mount the control in an area with average
CAUTION
room temperature and average relative
humidity.
Personal Injury Hazard.
Power supply can cause electrical shock.
Disconnect power supply before beginning
installation.
The following mounting instructions are for mounting
the H8908 on the wall next to the T8600. When install-
ing the H8908 at another location, modify the procedure
to fit the installation.
Location and Mounting
1. Hold the mounting template (included) next to the
T8600. Select the mounting side for the H8908.
The template is reversible for mounting on either
the left or right side of the T8600. See Fig. 2.
2. Mark the holes for the two mounting screws
(included). Then mark the hole for the low voltage
wiring on the template that corresponds with the
side selected in step 1.
The styling of the H8908 is designed to blend with the
latest T8600 family of Honeywell Chronotherm® IV
Deluxe Programmable Thermostats. A mounting tem-
plate is included for mounting the H8908 next to the
T8600. The H8908 can also be mounted at any other
convenient location in the living area or equipment
room. See Fig 1.
3. Remove the template and drill the holes.
4. Run low voltage wiring to the location and pull
about 6 in. (152 mm) of wire through the hole.
5. Plug the hole with nonflammable insulation to
prevent drafts from affecting the control opera-
tion.
NOTE: The H8908 electrical connections are not
shared with the thermostat.
® U.S. Registered Trademark
Copyright © 1999 Honeywell Inc. •
•All Rights Reserved
69- 1341
H8908B HUMIDISTAT H8908C DEHUMIDISTAT
WIRING
H8908B
WATER
2
SOLENOID
LEAD WIRE
CAUTION
TRANSFORMER
Personal Injury Hazard.
Power supply can cause electrical shock and
injury.
1
L2 L1
(HOT)
Disconnect power supply before installation or
servicing.
CURRENT
LO
SENSING
RELAY
C
HUMIDIFIER
HI
All wiring must comply with applicable local codes, ordi-
nances and regulations. Make wiring connections
according to humidifier (or dehumidifier/ventilator)
instructions, if available; otherwise, see typical wiring
diagrams in Fig. 5 through 12.
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
24V WIRING.
M13386
IMPORTANT
Fig. 7. Typical wiring diagram of current
sensing relay with humidifier.
Select models of fan centers include humidifer
taps so the current sensing relay or sail switch
is not needed.
SAIL
SWITCH
H8908B
If not using a current sensing relay or sail
switch, the humidifier must be energized dur-
ing blower motor cycles for proper operation.
2
TRANSFORMER
On multispeed blower applications, do not wire
the high voltage side of the transformer to the
same power source that services the furnace
blower. Premature transformer burnout can
occur.
1
HUMIDIFIER
L2 L1
(HOT)
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
24V WIRING.
M13385
On HE360 fan powered humidifier models,
only the two yellow wires are connected to the
control. The remaining two red wires are only
used with electronic humidity controls.
Fig. 8. Typical wiring diagram
of sail switch with humidifier.
FAN WIRING
TERMINALS
H8908B
1
L1
1
TO
SYSTEM
FAN
(HOT) POWER
2
H8908B
FAN CONTROL
SUPPLY
L2
HUMIDISTAT
TERMINALS
1
TRANSFORMER
HUMIDIFIER
HUMIDIFIER
FURNACE
FAN
MOTOR
1
24V WIRING.
NOTE: FOLLOW THE INSTALLATION INSTRUCTIONS
INCLUDED WITH THE STEAM HUMIDIFIER
TO WIRE THE SYSTEM FAN.
1
PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION
AS REQUIRED.
M13387
2
24 VAC WIRING.
M13368
Fig. 9. Typical wiring diagram for steam humidifiers.
Fig. 5. Typical wiring diagram for
system with fan interlock.
®
H8908C
CHRONOTHERM IV THERMOSTAT
B
O
L1
W
Y
R
G
(HOT) POWER
SUPPLY
L2
FAN CONTROL
DPST
H8908B
2
1
TRANSFORMER
HEATING
SWITCHING
RELAY OR
VALVE COIL
RELAY
2-SPEED
FAN
MOTOR
H
L
COOLING
CONTACTOR
COIL
FAN
RELAY
COIL
HUMIDIFIER
C
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
1
1
PROVIDE OVERLOAD PROTECTION AND
DISCONNECT MEANS AS REQUIRED.
M13384
M13366
24 VAC WIRING.
Fig. 10. Typical parallel wiring of humidity controller
with Chronotherm® IV Thermostat for
Fig. 6. Typical wiring diagram for system
with 2-speed fan motor.
dehumidification and mildew control.
3
69-1341
H8908B HUMIDISTAT H8908C DEHUMIDISTAT
ADJUSTMENTS
®
CHRONOTHERM IV THERMOSTAT
Humidity Control Adjustment
B
O
W
Y
R
To maintain optimum humidity control without causing
condensation on cold surfaces such as windows, the
homeowner must adjust the setpoint as the outdoor
temperature changes.
G
H8908C
HEATING
RELAY OR
VALVE COIL
To reduce the relative humidity, reduce the setpoint
approximately three percent relative humidity every 24
hours. To increase the relative humidity, increase the
sepoint approximately three percent relative humidity
every 24 hours.
COOLING
CONTACTOR
COIL
FAN
RELAY
COIL
Setpoint Adjustment
1
PROVIDE OVERLOAD PROTECTION
AND DISCONNECT MEANS AS REQUIRED.
1
M13367
Set the humidity setpoint according to the prevailing
outdoor temperature. See Table 1 for recommended
settings.
Fig. 11. Typical series wiring of humidity controller
with Chronotherm® IV Thermostat for
Table 1. Recommended Humidity
Controller Settings.
dehumidification and mildew control.
Outdoor Temperature
Recommended
Humidity
H8908C
°F
-20
-10
0
°C
-29
-23
-18
-12
-7
Controller Setting
15
20
25
30
35
40
VENTILATOR/DEHUMIDIFIER
DEHUMIDISTAT
TERMINALS
+10
+20
>+20
M13383
>-7
Fig. 12. Typical wiring diagram for HR150,
HR200, ER150 and ER200 Ventilator
or HD220 Dehumidifier applications.
OPERATION AND CHECKOUT
Place the system in operation and observe through at
least one complete cycle to make certain that all com-
ponents are functioning properly.
Home and Building Control
Honeywell Inc.
Home and Building Control
Honeywell Limited-Honeywell Limitée
Honeywell Plaza
P.O. Box 524
Minneapolis, MN 55408-0524
155 Gordon Baker Road
North York, Ontario
M2H 3N7
69-1341 G.H. 10-99 Printed in Taiwan R.O.C.
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