Johnson Controls W43A Humidistat Data Sheet
W43A Humidistat
The W43A Humidistat controls humidifying and/or
dehumidifying equipment. Typical uses include the
control of humidity by ventilation, air conditioning,
humidifiers, and dehumidifiers in residential,
commercial, and industrial installations.
The W43A has Single-Pole/Double-Throw (SPDT)
snap-acting contacts rated to switch 1/4 hp motors. It
has a wide setpoint range of 0 to 70% Relative
Humidity (RH), as well as “off” dial positions for
humidification and dehumidification. The differential of
the W43A is fixed at approximately 6% RH.
Master Catalog 125
Humidity Controls Section W
Product/Technical Bulletin W43A
Issue Date 1095
Figure 1: W43A Humidistat with Vertical Faceplate
Features and Benefits
❑
Human Hair Sensing Element Provides stable, accurate measurement
❑
1/4 hp (6A) Rated Contacts Permits direct operation of many fans in
commercial applications
❑
High/Low Adjustable Knob
Range Stops
❑
Enclosed Pennswitch Provides dust protection for contacts
❑
Mounting Plate Allows easy mounting and wiring without
Allows adjustments within a desired range
removing the cover
© 1995 Johnson Controls, Inc.
Part No. 24-8466-1, Rev. —
Code No. LIT-125715
1
ntroduction
I
IMPORTANT: The W43A Humidistat is designed for
use only as an operating control.
Where an operating control failure
would result in personal injury and/or
loss of property, it is the responsibility
of the installer to add devices (safety,
limit controls) or systems (alarm,
supervisory systems) that protect
against, or warn of, control failure.
The W43A Humidistat provides SPDT control for use
on low or line voltage applications. It has a
thermoplastic cover with Allen-head locking screw to
discourage unauthorized tampering. The sensing
element consists of carefully selected and processed
human hair.
An adjusting knob and easy-to-read dial allow quick
selection of the desired setpoint. The humidistat is
supplied with the faceplate installed for vertical
mounting and knob adjustment. However, a horizontal
faceplate is enclosed for horizontal mounting and knob
adjustment if desired.
Table 1: Humidity Settings
Outside Temperature Suggested Humidity
Setting
-20°F (-29°C) and Below 15% RH
-10°F (-23°C) 20% RH
0°F (-18°C) 25% RH
10°F (-12°C) 30% RH
20°F (-7°C) 35% RH
Above 20°F (-7°C) 40% RH or Higher as Desired
nstallation
I
Supplies Needed
• 2 x 4 in. (51 x 102 mm) wall box (field supplied)
• 3-wire cable (field supplied)
• screwdriver (slotted standard)
• marking pencil
• wire strippers
umidity Settings
H
The humidistat has a setpoint range of 0 to 70% RH,
as well as humidification off (HUM OFF) and
dehumidification off (DEH OFF) positions. At the HUM
OFF position, the C to L terminal circuit is open and
the C to H terminal circuit is closed.
At the DEH OFF position, the C to H terminal circuit is
open and the C to L terminal controls the humidification
equipment.
At any given setpoint, the C to L circuit closes on a
decrease in relative humidity, and the C to H circuit
closes on an increase in relative humidity.
The usual setting in winter is 30 to 40% RH. Lower
settings may be necessary in extremely cold weather
to prevent condensation on windows, doors, etc. The
same setting should be used where reduction of
humidity by means of exhaust fans is provided in wellconstructed homes. Summer settings on air
conditioning or dehumidifying equipment will usually be
near 50% RH.
The suggested indoor humidity at 70°F (21°C) for
residential applications on humidifying or dehumidifying
equipment in winter is shown in Table 1.
Location Considerations
Locate the W43A Humidistat as follows:
• on an inside wall away from ranges, sinks,
bathrooms, or other areas of extreme moisture and
temperature
• where natural air circulation is unrestricted
• where lamps, sunlight, fireplaces, heat registers,
radiators, concealed air ducts or pipes, or room
occupants will not affect its operation
2 W43A Humidistat Product/Technical Bulletin
Dimensions
1.59
40
6-32 Mounting
Screws (2 Places)
1.20
30
0.69
18
2.96
75
1.27
32
Mounting and Wiring
4.71
120
1.28
33
0.25
6
1.41
36
Figure 2: W43A Dimensions (in./mm)
2.34
59
3.22
82
0.80
20
Mounting Plate
Locking Screw
Adjustment
Knob
Optional
Concealed
Adjustment
Faceplate
Grounding
Screw
Mounting
Plate
Vertical
Faceplate
Cover
Locking Screw
Figure 3: W43A Humidistat
Wall
Box
W43A Humidistat Product/Technical Bulletin 3
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