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

Part No. 24-8466-1, Rev. — Code No. LIT-125715

ntroduction

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

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

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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