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FORM NO. 747-23 Rev. B  (FILE 12549)

Litho in U.S.A.

8

ELECTRICAL

NOTE: The humidifier has a built-in "Humidity Control" which is an adjustable 

thermostat that completes the humidifier motor circuit on rising duct 

temperature. The thermostat senses the peaks and valleys of the modulating 

duct temperature caused by the furnace heating cycle. When the control is set 

on "HIGH", the humidifier will operate a greater percentage of the furnace 

cycle; and when set on "LOW", it will operate a lesser percentage of the cycle. 

A wall or duct mounted humidistat becomes an optional accessory with the 

built-in "Humidity Control". 

WIRING 24 VOLT MODEL HUMIDISTAT OPTIONAL

The humidifier does not require connection to the furnace blower circuit. 

Connect the wire supplied to the two wires on the humidifier. Slide the plastic 

tubing over the terminals. Connect the two wires to the transformer and plug 

transformer into a 115 volt electrical outlet that will remain on at all times. Do 

not use an extension cord. If a humidistat is used in conjunction with the built-

in "Humidity Control", connect the humidistat in series with the humidifier as 

shown and turn the "Humidity Control" to the "ON" position. ALL WIRING 

SHOULD COMPLY WITH LOCAL ELECTRICAL CODES.

TEST RUN HUMIDIFIER

Turn on the water supply and electrical power. Set the "Humidity Control" to the "ON" position. The humidifier motor should turn the drum at 1 

RPM. The float valve should maintain a water level of approximately 1-1/2 inches. The "OFF" position on the "Humidity Control" corresponds to a 

trunk duct temperature of 160ºF. and the "ON" position to a temperature of 70ºF. With the control set on "MED" (115ºF.), the humidifier will run 

approximately 50% of the available furnace operating time. Initially the "Humidity Control" may be left on "MED" with instructions to the user to 

adjust higher or lower as required. 

The mid-range set point for warm air heating systems employing heat pumps will be in the "HIGH" range because of the lower trunk duct 

temperatures. A humidistat may be required on heat pump systems.

INSTALLER: Please instruct user on the importance of frequent draining through the quick-drain device to keep water fresh and reduce the 

mineral concentration in the water pan.

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22

1

2

3

5

6

9

10
11

12
13
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15
16

17

18

4

7 8

19

20

27

26

23

24

25

PARTS LIST FOR HUMIDIFIER

FILL OUT AND MAIL THIS 
WARRANTY CARD AND 
LITERATURE REQUEST FORM

A

IR

C

LEANERS AND 

A

IR

P

URIFIERS

H

UMIDIFIERS

D

IGITAL

H

UMIDITY

G

AGE

A

IR

F

ILTER

G

AGE

F

UEL

O

IL

F

ILTERS AND 

A

CCESSORIES

1. 727-7 DRUM SHAFT

2. P-188 RETAINER CLIP

3. 727-5 DRUM END (2 REQ'D)

4. 727-4 DRUM ASSEMBLY

5. 727-12 EVAP. SLEEVE

6. 747-28 MOTOR ASSY.

7. P187 COMPRESSION UNION 

8. 747-35 "L" TUBE ASSY.

9. 975-3 ORIFICE NUT

10. 747-11 VALVE WASHER

11. 727-8 SPLASH GUARD

12. 975-6 SHIELD - VALVE

13. 727-24 FITTING - ORIFICE

14. 975-1 VALVE SEAT

15. P118 COTTER PIN

16. 727-34 ARM - FLOAT

17. 727-32 FLOAT BLOCK

18. 747-29 FLOAT VALVE ASSY. 

19. 747-7 MOUNTING FRAME

20. 747-30 WINDOW

21. 45-1 DRUM BEARING

22. 747-1 WATER PAN

23. 1099-9 THUMB NUT

24. 747-26 HUMIDITY CONTROL

25. 747-21 NAME PLATE

26. 747-5 QUICK DRAIN

27. P185 CLAMP

PARTS NOT SHOWN:

800UST SADDLE VALVE

727-48 LEAD WIRE ASSY.

747-36 TRANSFORMER 

747-9 MOUNTING TEMPLATE 

747-38 WATER SUPPLY TUBE KIT 

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