Aprilaire 400, 400A, 400M Installation Manual

No. 45 Water Panel Evaporator Installation Page 1

1. Note Humidifier Control setting and turn dial to the “OFF” position.

WARNING

120 Volts may cause serious injury from electrical shock. Disconnect power and shut off water supply before servicing.

2. Turn off water supply. Turn the integral bypass damper (3) to the “SUMMER” position.

Aprilaire Models 400, 400A & 400M

6

4

7

1

1. Front Cover

2. Feed Tube

3. Integral Bypass Damper

4. Water Panel Evaporative Assembly

5. Distribution Tray

6. “V” Notches

3

11

7. Water Panel Evaporator

8. Scale Control Insert/Float Chamber

9. Overflow Drain Line

10. Float Cover

11. Float

12. Water Level Sensor Assembly

5

10

12

9

8

90-1077

3. Press the tabs in the latches on the top and bottom of front cover (1) and pull cover off base
with both hands.

4. Carefully pull the plastic feed tube (2) out of the distribution tray (5) at the top of the Water
Panel evaporative assembly (4). Tip the Water Panel evaporative assembly forward and lift it
out of the humidifier. Do not tip the Water Panel evaporative assembly more than needed to
clear the housing to avoid over-bending the water level sensor assembly (12).

5. Unsnap the distribution tray (5) from the scale control insert (8). Follow the instructions below
depending upon the type of distribution tray in your humidifier:

For trays with a synthetic fabric liner: Lightly scrape out or brush off any mineral deposits,

being careful not to stretch or loosen the synthetic fabric liner. Soaking the tray in vinegar or a
lime-removing agent is helpful when trying to remove stubborn mineral deposits.

For trays with granular coating: Do not scrape off the granular coating, but lightly

scrape out any mineral deposits and clean the “V” notches (6). This textured surface helps
ensure even water flow for maximum performance.

6. Slide the used Water Panel evaporator (7) out of the scale control insert/float chamber and
dispose of the Water Panel.

7. Remove the float cover (10) and inspect the floats (11) and float chamber for mineral build-up.

2

Remove deposits as needed from floats, float chamber and scale control insert. Wash the
parts with a disinfecting cleaner. Reassemble the floats and float cover. Make sure stems of
both floats extend through openings in float cover and that floats move freely up and down.

8. Inspect the plastic feed tube (2) by gently flexing it and looking for cracks or signs of wear.
Replace tube if it is cracked, brittle, or has been damaged.

9. Slide a new Aprilaire No. 45 Water Panel evaporator (7) into the scale control insert/float
chamber (8). Snap the distribution tray (5) back on the scale control insert (8).

10. Reinstall the Water Panel evaporative assembly (4) into the humidifier. Take care not to
over-bend the water level sensor assembly. Push the top of the Water Panel evaporative
assembly firmly back until it snaps into place.

11. Push the end of the feed tube back firmly into the distribution tray. Replace the front cover.

12. Under normal operation the overflow drain line (9) will never have water in it. However,
inspect it for mineral deposits and replace if necessary. Make sure the drain line has a
constant downward slope and is not flattened or blocked.

13. Turn on the water supply. Return integral bypass damper to appropriate position.

14. Check system operation:

Manual Humidifier Control (Model 400M): With the HVAC blower operating, turn up

Humidifier Control and check system operation.

Automatic Humidifier Control (Models 400 & 400A): (Automatic or Manual mode)

Check system operation and reset Change Water Panel indicator by setting the knob to
“Test/Reset”. With furnace blower operating and furnace calling for heat, humidifier will
operate for one minute. Do not leave in Test Mode as humidifier will not operate.

15. Set Humidifier Control to its original position.

Aprilaire Models 400, 400A & 400M

90-1077

1. Front Cover

2. Feed Tube

3. Integral Bypass Damper

4. Water Panel Evaporative Assembly

5. Distribution Tray

6. “V” Notches

7. Water Panel Evaporator

8. Scale Control Insert/Float Chamber

9. Overflow Drain Line

10. Float Cover

11. Float

12. Water Level Sensor Assembly

1

4

5

6

7

8

2

9

3

10

11

12

No. 45 Water Panel Evaporator Installation Page 2

Water Line Inspection and Service

Instructions for All Models

The humidifier is equipped with an

in-line water strainer. See the following

instructions for strainer cleaning.

WATER
FEED TUBE

OUTLET
COMPRESSION
NUT

ORIFICE

SOLENOID

90-1053

1. Disconnect electrical power to the furnace and shut off
water supply.

2. Disconnect the water line at the inlet compression nut.

3. Remove the in-line strainer from inside the inlet side of
the valve by using a small nail or wire.

4. Flush the in-line strainer clean or replace with a new
strainer, Service Department, Part No. 4004.

5. Reconnect the inlet water line. Double Wrench to

Prevent Leaking.

6. Disconnect the water feed tube at the outlet
compression nut.

7. Inspect the water feed tube (plastic only) by gently
flexing it and looking for cracks or signs of wear. Replace
tube if it is cracked, brittle, or has been damaged.

8. Remove the orifice from the copper or plastic water feed
tube and make sure this small opening is unplugged.

9. Replace the orifice with Part No. 4231 (yellow) and
reconnect the water feed tube. Double Wrench to

Prevent Leaking.

10. Turn on water supply and reconnect electrical power to
the furnace.

VALVE

INLET

IN-LINE
STRAINER

INLET
COMPRESSION
NUT

10010437 6.13
B2206152A

P.O. Box 1467 • Madison, WI 53701-1467 • Phone: [phone] • Fax: [phone] • www.aprilaire.com

© 2013 Aprilaire – A division of

Research Products Corporation