Maintenance Instructions:
Aprilaire Models 550, 550A, & 558
1. Note the Humidifier Control setting and turn dial to the “OFF” position.
2. Turn off water supply. Move the integral bypass damper (10), if present, to the
SUMMER position.
3. At the side of the humidifier opposite the airflow duct, pull front cover (1) off
holding with both hands and set aside.
4. Carefully pull the feed tube (2) out of the nozzle (3) at the top of the
evaporative assembly (4). Pull this assembly out by grasping at the top and
tipping out.
5. Remove the distribution tray (5) from the Water Panel evaporator assembly
(4) by unsnapping the plastic ends of the scale control insert (8), from the
tabs at the end of the tray. Follow the instructions below depending upon the
type of distribution tray in your humidifier.
a. 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.
b. 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. If the granular coating has been removed,
place several drops of liquid dishwashing soap on the distribution tray.
This will only need to be done once if there is no granular coating.
6. Slide the Water Panel evaporator (7) out of the scale control insert (8). Clean
the scale control insert of mineral deposits. Slide the new Water Panel
evaporator into the scale control insert with the colored spot up and snap the
distribution tray (5) back into place.
7. Inspect feed tube (plastic only) by gently flexing it and looking for cracks or
signs of wear. Replaced tube if it is cracked, brittle or has been damaged.
8. Reinstall the Water Panel evaporator assembly (4) into the humidifier by
fitting its drain into the round receptacle at the base of the humidifier. Push
the assembly in at the top against the beveled tabs that will hold it in place.
Push the end of the feed tube (2) firmly back into the nozzle (3) and replace
the front cover (1).
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