Aprilaire 220 Service Manual page 8

III. LEAKING WATER
The Models 220 and 224 are provided with a cover over the distribution tray. These covers
are quite effective in minimizing water bubbling out of the feed tray up to approximately
0.4 in. static pressure. A damper should be included in the bypass between the supply and
return plenum to relieve the pressure that can be created by zone dampers completely
closed with the furnace blower still operating. We might also suggest that zone dampers
be slightly cracked to relieve the pressure and therefore reduce the static pressure in the
plenum.
IV. NOISE
— See Page 4.
V. Model 400 troubleshooting Procedure
The two floats in the chambers at the base of the scale control insert activate switches in
the water level sensor assembly, which control power to the solenoid valve. The float on
the right is the primary control mechanism. When the water level in the chamber on the
right rises, the float disconnects power to the solenoid valve, shutting off the water. As the
water level drops, the float activates the switch, energizing the solenoid valve, which
opens and sends water to the distributor tray. The float in the chamber on the left controls
an over-flow protection circuit. If the primary float fails to shut off the solenoid valve, water
will flow into the chamber on the left, raising that float and disconnecting power to the
solenoid valve. If both floats fail to disconnect power to the solenoid valve or if the valve
fails in the open position, water will flow into the safety overflow line.
●
Check both floats, the chambers, and the float cover. Make sure the float cover is
properly snapped into place and that both floats move freely up and down.
●
Check that the solenoid valve closes when de-energized.
●
Check the electrical continuity of the water level sensor circuit. With both floats
down, the circuit should be closed. With either float up, the circuit should be open.
VI. GENERAL MAINTENANCE
— See Page 4.
— See Pages 4 and 5.
- 7 -