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1. Front Cover
2. Feed Tube
3. Integral 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 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 from the scale control insert (8). Lightly scrape out any
calcium deposits and clean the “V” notches (6) but do not scrape off the granular
coating. 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. Inspect the overflow hose (9) to make sure it is open.
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. Slide a new Aprilaire no. 45 water panel into the scale control insert/float chamber. Snap
the distribution tray back on the scale control insert.
9. Reinstall the water panel evaporator assembly 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.
10. Push the end of the feed tube back firmly into the distribution tray. Reset the damper to
desired position. Replace the front cover.
11. Turn on the water supply.
12. 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.
13. Reset Humidifier Control to its original position. Check operation.
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
MODEL
400