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MODEL 400
- 10 -
1. Front Cover
2. Feed Tube
3. Integral Bypass Damper
4. Water Panel Evaporator
Assembly
5. Distribution Tray
6. “V” Notches
7. Water Panel
8. Scale Control Insert/Float
Chamber
9. Overflow Hose
10. Float Cover
11. Float
12. Water Level Sensor Assembly
1. Note Humidifier Control setting and turn dial to the “Off” position.
2. Turn off water supply. Turn the integral bypass damper (3) to the SUMMER position.
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
evaporator assembly (4). Tip the Water Panel evaporator assembly forward and lift it out of the
humidifier. Do not tip the Water Panel evaporator 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. See page 3 if removed.
6. Slide the used water panel (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. 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 (7) into the scale control insert/float chamber (8). Snap the
distribution tray (5) back on the scale control insert (8).
10. Re-install the Water Panel evaporator assembly (4) into the humidifier. Take care not to over-bend the
water level sensor assembly. Push the top of the Water Panel evaporator 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. Remove the overflow hose (9) from the bottom of the unit and flex it to loosen any mineral deposits or
blockage. Then flush with water under pressure and slip it back onto the drain fitting. Make sure the
drain hose 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:
Humidifier Control
: (Automatic or Manual) 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. Reset Humidifier Control to its original position.
MAINTENANCE INSTRUCTIONS FOR
APRILAIRE HUMIDIFIER MODEL 400
CAUTION! Sudden operation may cause personal injury or
property damage. Turn Humidifier Control to “off” or
lowest setting before servicing.
MODEL
400