I. PRINCIPLE OF OPERATION
The purpose of the Aprilaire®Dehumidifier is to keep humidity in the house at acceptable limits to
reduce the unwanted effects of high humidity. The dehumidifier gathers data from the HVAC system
and measures the condition of the house air to decide when to run. An integrated air cycling feature
can activate the HVAC blower to cycle air through the house to balance the indoor conditions. The
dehumidifier can also operate an optional ventilation damper to bring in outside air.
II. OPERATING INSTRUCTIONS
There are three adjustable settings: the dryness setting, the air cycle period and the air cycle time
within that period. The dehumidifier dryness can be set from
“1” or
“LESS” to “7” or “MORE” based on
desired comfort level. Most installations should be initially set between “3” and “5” or “NORMAL”
setting; however this can be adjusted to your individual needs. Air cycle period is set using the dip
switches, and the potentiometer is used to set the air cycle time which are both located on the control
board under the knob and are set during installation. If the cycle period is set to 1 hour and the cycle
time potentiometer is set to 20 minutes, you will get 20 minutes of air cycling every hour. It is important
to understand that the air cycling requirement – 20 minutes per hour in this example – may be satisfied
by a heating, cooling, or fan call initiated by your thermostat, or if such calls do not satisfy the air
cycling requirement, from a blower call initiated by the dehumidifier itself.
1. ADJUSTING THE DEHUMIDIFIER SET POINT
Use the main control knob (Figure 1) on the outside
of the unit to set the dehumidifier dryness setting.
Start with a “NORMAL” setting for most installations.
Moving the knob clockwise to “MORE” will make
conditions drier. Moving the knob toward “LESS”
allows for higher moisture levels.
Based on the indoor temperature, use the following
table to determine the control knob setting to reach
the desired RH value. The dehumidifier will work to
achieve these values.
2. SETTING THE AIR CYCLE PERIOD AND CYCLE TIME
The air cycle period and cycle time are set during installation to meet the individual needs of your
home. Detailed instructions are included in the dehumidifier installation manual.
III. OUTDOOR VENTILATION OPTION
If an Aprilaire®Normally-Closed Damper (Model 6506) was installed in the HVAC outside air intake,
then this damper will open whenever air cycling is active. This allows ventilation of outside air to be
included into the air cycling of your indoor air.
IV. MAINTENANCE
AIR FILTER
Under normal circumstances, the filter in the dehumidifier should be cleaned or replaced once a year.
A clean filter is necessary to prevent damage to the dehumidifier and allow it to function at full
capacity. To remove the filter, first unplug or disconnect power to the dehumidifier, then remove the air
filter via the access panel on the side of the dehumidifier. To clean, flush with warm water and
detergent solution. After a clean or new filter is reinstalled, replace the access panel and reconnect
power to the dehumidifier. The replacement filter for the dehumidifier is Model 4510 and is available
from your installing contractor or from most other HVAC contractors in your area.
DRAIN
The drain trap or outlet should be checked and cleaned o debris annually by a quali ied
service pro essional.
NOTE: The drain trap needs to be primed with water prior to start-up and after extended periods of
unit shut down (winter months).
VENTILATION CONTROL LIMITS
In a standard installation, your Aprilaire®Dehumidifier will use measurements of outdoor temperature
along with the user adjustable time settings to determine when to ventilate with outdoor air. The
ventilation damper will not bring in outside air if the outside temperature is above 100 F or below 0 F.
The ventilation damper will allow outside air to be brought in when the temperature is between 20 F
and 0 F only during a heat call. In timed mode, outdoor air is taken based on the time setting only,
regardless of temperature.
%RH (± 5%) based on Control Knob Setting and Indoor Temperature
Control Knob Indoor Temperature (°F)
Setting 65 70 75 80
1 - “LESS” 84% 71% 60%
2 86% 73% 61% 52%
3 - “NORMAL” 74% 63% 53% 45%
4 - “NORMAL” 64% 54% 45% 39%
5 - “NORMAL” 55% 46% 39% 33%
6 47% 39% 33% 28%
7 - “MORE” 40% 34% 28% 24%
EXAMPLE: At an indoor
temperature of 75 F with a
dehumidifier control knob
setting of 3, the dehumidifier
will work to achieve an RH
value of 53%.
NOTES:
1. %RH values are ±5% and
are to be used as a GUIDE
ONLY for initial set-up.
2. Indoor Temperature is
measured at the inlet to
the Model 1750A/1770A.
FIGURE 1
90-1327
