Aprilaire 1720 User manual

Wire
Routing
Port
Wiring
Access
Filter
Access
Humidity
Control Inlet
Drain
On/Off
Switch
Filter
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Service
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PortOutlet
Installation, Safety & Maintenance Manual
Model 1720
Dehumidifier
INSTALLER – PLEASE NOTE!
1. Installation must conform to all applicable codes.
2. A dedicated 20 Amp circuit is required for proper operation of the dehumidifier. If a dedicated circuit is not
available, do not install unit. Dehumidifier must be plugged in directly to an outlet. Do not use an extension cord.
3. For protection of the compressor, unit must be transported and installed in an upright position.
If the unit was shipped or stored on its side, a 24 hour settling period is required before running the unit.
TABLE OF CONTENTS
Safety Instructions . . . . . . . . . . . . . . .2
Overview . . . . . . . . . . . . . . . . . . . . . . .2
Specifications . . . . . . . . . . . . . . . . . . .2
Location Notes . . . . . . . . . . . . . . . . . .2
Ducting . . . . . . . . . . . . . . . . . . . . . . . .3
Drain Line . . . . . . . . . . . . . . . . . . . . . .3
Hanging . . . . . . . . . . . . . . . . . . . . . . .3
Installations
Whole Building . . . . . . . . . . . . . . . . . .4
Localized . . . . . . . . . . . . . . . . . . . . . . .6
Whole Building / Localized
Convertible . . . . . . . . . . . . . . . . . . . . .8
Ventilation and Fan Cycling . . . . . . .10
Float Switch . . . . . . . . . . . . . . . . . . .11
Dip Switch Definitions . . . . . . . . . . .12
System Checkout . . . . . . . . . . . . . . .13
System Setup . . . . . . . . . . . . . . . . . .13
Maintenance . . . . . . . . . . . . . . . . . .13
Troubleshooting . . . . . . . . . . . . . . . .14
Sequences
of Operations . . . . . . . . . . . . . . . . . .15
Warranty . . . . . . . . . . . . . . .Back Cover

2
SAFETY INSTRUCTIONS
OVERVIEW
SPECIFICATIONS
WARNING
• This product must be installed by a qualified heating and air conditioning contractor. Failure to do so could result in
serious injury from electrical shock or damage to product.
• 120 volts may cause serious injury from electric shock. Disconnect electrical power before starting installation.
Leave power disconnected until installation is completed.
• Sharp edges may cause serious injury from cuts. Use care when cutting plenum openings and handling ductwork.
• Unit weight and dropping may cause personal injury or equipment damage. Handle with care.
Overall Dimensions:
21”W x 243⁄4”L x 21”H (mounting feet fully engaged)
21”W x 243⁄4”L x 221⁄2”H (mounting feet fully extended)
Weight: 100 lbs
Capacity: 150 pints per day @ 60%RH, 80°F
(ANSI/AHAM DH-1-2003 conditions)
Power: 115 VAC, 14 Amps. Unit is equipped with an
8 ft. grounded power cord.
The purpose of the Aprilaire Model 1720 Dehumidifier is to keep the humidity in the building at acceptable limits to reduce
the unwanted effects of high humidity. The dehumidifier will measure the dewpoint of the building to decide if it needs to run.
The dryness set point can be adjusted with the control knob on the inlet side of the unit.
An integrated air cycling feature can be used to turn on the HVAC fan to cycle the air through the building to balance the indoor
conditions. This feature is set up during installation based on building size and building manager preference. An optional
ventilation damper can also be installed to bring in outside air during air cycling.
LOCATION NOTES
The dehumidifier can be installed in a wide variety of locations (including unconditioned spaces), provided the ambient conditions
are between 40°F and 150°F. Note the following installation requirements:
• All duct work must be insulated.
• Unit should be placed in a drain pan with overflow protection to prevent water damage in the event of a drain failure (above
ceiling installs).
• The condensate line should be insulated to prevent condensation on the outside of the condensate line.
• Precautions should be taken to assure that the unit does not operate in ambient conditions below 40°F or above 150°F.
• Unit is not designed for outdoor use.
Design Airflow: 500 CFM @ 0.8 in. w.c.
Filter: MERV 8 Filter
Cabinet Insulation: 1” foil faced EPS insulation
Inlet Air Operating Conditions: 40°F to 105°F
Ambient Air Operating Conditions: 40°F to 150°F
Refrigerant: R-22, 25 oz.

The included condensate trap
must be installed to the Model
1720. Use PVC primer and
cement to connect the trap to the
drain outlet on the Model 1720.
The drain outlet is located near
the On/Off toggle switch. Note
orientation of trap prior to
cementing. The high side of the
trap mates with the Model 1720. The adjustable legs on
the Model 1720 must be disengaged approximately 1” to
accommodate the trap. Complete the assembly by piping
the trap to a drain. The trap must be primed with water
prior to start-up.
If the 1720 is installed above a ceiling or in an area where
flooding is a potential problem, it should be installed in a
secondary drain pan with a condensate overflow safety
switch. See page 11 for condensate overflow safety
switch wiring.
If hanging the unit, use two unistruts to support the base
on the outside edges of the feet locations. There must
be at least 20” of clearance in front of one of the filter
access doors to allow removal of the filter.
3
DRAIN LINE
HANGING
DUCTING
The Aprilaire Dehumidifier is supplied with two
8” round collars. These are packaged with a
condensate trap inside the unit behind the filter
access panel. When installing the collars make sure
the foam seal uniformly contacts the cabinet and
secure with 4 screws (not included). UL approved
8” diameter, insulated flexible duct is recommended
for all connections. Rigid metal duct may be used.
The duct should be capable of handling at least
2” w.c. pressure. All joints and seams must be sealed.
Design air flow is 500 CFM @ 0.8” w.c. This is
equivalent to approximately 100 ft. of 8” duct on the
inlet and outlet side of the dehumidifier. Elbows,
turns and the static pressure of the HVAC equipment
will affect the airflow through the dehumidifier.
• For optimal moisture removal, airflow should be at or above
500 CFM.
• The total static pressure across the dehumidifier must not
exceed 1.5” w.c. Check all pressures with the HVAC fan on.
• The outlet from the dehumidifier to the HVAC supply duct must be
located at least 6” downstream of the cooling coil.
• If connected to HVAC ductwork, the dehumidifier inlet must be located
at least 6” upstream of the HVAC system air cleaner. This will prevent
any trapped particulates from being drawn into the dehumidifier.
• If UV Germicidal lamps are installed in the HVAC system, use
appropriate methods to protect the flexible duct from the UV light.
• If air noise is a problem, install at least 5 feet of acoustical flexible
duct on the outlet and inlet of the dehumidifier.
21/2”
1/2”
Drain Outlet
Drain Trap
High Side Low Side
FIGURE 1
90-961
3“ MIN
CLEARANCE FOR
ACCESS PANEL
20” MINUMUM
CLEARANCE FOR FILTER
(EITHER SIDE)
6" MIN CLEARANCE
FOR ACCESS PANEL
FILTER
TOP VIEW
FIGURE 2
90-970

4
WHOLE BUILDING INSTALLATION AND OPERATION
In this configuration the dehumidifier will pull air from the return duct. The air passes through the dehumidifier, where moisture is
removed, and then returned to the HVAC system downstream of the cooling coil in the supply plenum. This installation is used
when the HVAC unit conditions the area where dehumidification is needed.
1 – 6508 Normally Closed Power Open Damper
Duct Work
24 VAC Transformer (10 VA minimum)
Thermostat Wire
REQUIRED COMPONENTS OPTIONAL COMPONENTS
6506 Ventilation Damper
24 VAC Transformer (10 VA minimum) for Ventilation Damper
8052 Outdoor Temperature Sensor
Normally Closed Condensate Overflow Safety Switch
90-973
FIGURE 3 – DUCTING

5
WHOLE BUILDING INSTALLATION AND OPERATION (CONTINUED)
THERMOSTAT HVAC EQUIPMENT
TRANSFORMER
(10 VA min)
24 VAC
DAMPER
N.C. BACKFLOW CONTROL
DEHUMIDIFIER
DAMPERS
Rf Y -WGhGs
Cf
VENT
HVAC EQUIP REMOTE
DEH B +A
R
C
W
YY
W
G
C
R
G
ODT
SENSORSWITCH
FLOAT
FIGURE 4 – WIRING
90-962
FIGURE 5 – SETTINGS
90-963
CYCLE TIME
TEST
60
OFF
0
MIN
MIN.
30
MIN.
ON
1234
2 HOUR
3 HOUR
30 MIN.
1 HOUR
CYCLE PERIOD
4321
ON
VENT-TIMED
HVAC FAN
SYSTEM SETUP
ON
MODEL 70
CONVERTIBLE
HVAC FAN
WHL HOUSE
VENT-AUTO
MODEL 70
OFF
Standard Fan Cycling Ventilation
OFF OFF OFF
See pages 10-11 See pages 10-11 See pages 10-11
OFF OFF OFF
OFF ON OFF
Standard Fan Cycling Ventilation
OFF See pages 10-11 See pages 10-11
ON See pages 10-11 See pages 10-11
OFF See pages 10-11 See pages 10-11
OFF See pages 10-11 See pages 10-11
Standard Fan Cycling Ventilation
OFF See pages 10-11 See pages 10-11
See page 10 for ventilation control wiring instructions.
See page 10 for fan cycling wiring instructions.
See page 11 for float switch wiring instructions.

6
LOCALIZED INSTALLATION AND OPERATION
In this configuration the dehumidifier will pull air from an area in the building. The air passes through the dehumidifier, where
moisture is removed, and then is returned to the area. This installation is used when the HVAC unit conditions an area other than
where dehumidification is needed, or in an area that needs supplemental dehumidification.
Duct Work
Grilles
REQUIRED COMPONENTS OPTIONAL COMPONENTS
24 VAC Transformer (10 VA minimum) for Ventilation Damper
Thermostat Wire
6506 Ventilation Damper
8052 Outdoor Temperature Sensor
Normally Closed Condensate Overflow Safety Switch
10’ MIN
10’ MIN
90-973
FIGURE 6 – DUCTING

7
LOCALIZED INSTALLATION AND OPERATION (CONTINUED)
THERMOSTAT HVAC EQUIPMENT
CONTROL
DEHUMIDIFIER
DAMPERS
Rf Y -WGhGs
Cf
VENT
HVAC EQUIP REMOTE
DEH B +A
R
C
W
Y
Y
W
G
C
R
G
ODT
SENSORSWITCH
FLOAT
FIGURE 7 – WIRING
90-964
FIGURE 8 – SETTINGS
90-965
CYCLE TIME
TEST
60
OFF
0
MIN
MIN.
30
MIN.
ON
1234
2 HOUR
3 HOUR
30 MIN.
1 HOUR
CYCLE PERIOD
4321
ON
VENT-TIMED
HVAC FAN
SYSTEM SETUP
ON
MODEL 70
CONVERTIBLE
HVAC FAN
WHL HOUSE
VENT-AUTO
MODEL 70
OFF
Standard Fan Cycling Ventilation
OFF OFF OFF
See pages 10-11 See pages 10-11 See pages 10-11
ON ON ON
OFF ON OFF
Standard Fan Cycling Ventilation
OFF See pages 10-11 See pages 10-11
ON See pages 10-11 See pages 10-11
OFF See pages 10-11 See pages 10-11
OFF See pages 10-11 See pages 10-11
Standard Fan Cycling Ventilation
OFF See pages 10-11 See pages 10-11
See page 10 for ventilation control wiring instructions.
See page 10 for fan cycling wiring instructions.
See page 11 for float switch wiring instructions.

8
WHOLE BUILDING / LOCALIZED CONVERTIBLE INSTALLATION AND OPERATION
In this configuration the dehumidifier will automatically switch between whole-building dehumidification when the HVAC
equipment is on, and localized dehumidification when the equipment is off. This installation is used to dehumidify a whole
building and a separate unconditioned space.
2 – 6508 Normally Closed Power Open Damper
2 – 6608 Normally Open Power Closed Damper
Duct Work
24 VAC Transformer (40 VA minimum)
Thermostat Wire
REQUIRED COMPONENTS OPTIONAL COMPONENTS
6506 Ventilation Damper
24 VAC Transformer (10 VA minimum) for Ventilation Damper
8052 Outdoor Temperature Sensor
Normally Closed Condensate Overflow Safety Switch
OPTIONAL
OUTDOOR AIR INTAKE
6“ MIN
RETURN
AIRFLOW
6“ MIN
AIR CLEANERCOOLING COIL
OPTIONAL
N.C. DAMPER
HVAC UNIT
1720
N.O. DAMPER
3‘ MIN
SUPPLY
AIRFLOW
N.O. DAMPER
N.C. DAMPER
N.C. DAMPER
RETURN FROM
UNCONDITIONED
SPACE
SUPPLY TO
UNCONDITIONED
SPACE
FIGURE 9 – DUCTING
90-947

9
WHOLE BUILDING / LOCALIZED CONVERTIBLE INSTALLATION AND OPERATION (CONTINUED)
THERMOSTAT HVAC EQUIPMENT
DEHUMIDIFIER SYSTEM DAMPERS CONTROL
DEHUMIDIFIER
TRANSFORMER
(40 VA min)
24 VAC
DAMPERS
Rf Y -WGhGs
Cf
VENT
HVAC EQUIP. REMOTE
DEH B +A
R
C
W
YY
W
G
C
R
G
ODT
SENSORSWITCH
FLOAT
WIRE NUT
FIGURE 10 – WIRING
90-966
FIGURE 11 – SETTINGS
90-965
CYCLE TIME
TEST
60
OFF
0
MIN
MIN.
30
MIN.
ON
1234
2 HOUR
3 HOUR
30 MIN.
1 HOUR
CYCLE PERIOD
4321
ON
VENT-TIMED
HVAC FAN
SYSTEM SETUP
ON
MODEL 70
CONVERTIBLE
HVAC FAN
WHL HOUSE
VENT-AUTO
MODEL 70
OFF
Standard Fan Cycling Ventilation
OFF OFF OFF
OFF OFF OFF
ON ON ON
OFF ON OFF
Standard Fan Cycling Ventilation
OFF See pages 10-11 See pages 10-11
ON See pages 10-11 See pages 10-11
OFF See pages 10-11 See pages 10-11
OFF See pages 10-11 See pages 10-11
Standard Fan Cycling Ventilation
OFF See pages 10-11 See pages 10-11
See page 10 for ventilation control wiring instructions.
See page 10 for fan cycling wiring instructions.
See page 11 for float switch wiring instructions.

10
First, set the 1/2, 1, 2 or 3 hour period by
setting the CYCLE PERIOD dip switches to determine how often the dehumidifier should look to
ventilate or cycle the HVAC fan. The factory default setting is 1 hour.
Next, use the CYCLE TIME dial to determine how long during every cycle period the HVAC fan
should operate. Adjust the dial from OFF to between 1 to 60 minutes. This will give you HVAC fan
operation from 1 to 60 minutes every 1/2, 1, 2 or 3 hours. A call for heat, cooling or fan from the
HVAC equipment will often satisfy the run time requirement. If not, the dehumidifier will turn on
the HVAC fan to assure that the cycle time is met. For example: If the building requires
ventilation of 20 minutes every two hours set the CYCLE PERIOD Dip Switch for 2 hours
to ON, turn OFF the 1 HOUR Dip Switch and rotate the CYCLE TIME to 20 minutes. If the
HVAC equipment has only run for 10 minutes, the dehumidifier will turn on the HVAC
fan for 10 minutes at the end of the 2 hours to assure the ventilation / fan cycling time.
Finally, if using the Ventilation Damper, determine if the ventilation should be restricted based
on outdoor temperature. Set the VENT-AUTO / VENT-TIMED dip switch to VENT-AUTO
(see Figure 15) to prevent opening the ventilation damper if the outdoor air is above 100°F,
below 0°F or except with a heat call between 20°F and 0°F. In the VENT-TIMED setting the
ventilation damper is activated regardless of outdoor conditions. Note: The Outdoor
Temperature Sensor (Model 8052) must be installed for this to work.
You can also check the wiring of the dehumidifier to the HVAC equipment. If you rotate the
CYCLE TIME dial to TEST, the HVAC fan should come on and the Ventilation Damper
(if equipped) should open. DO NOT leave the CYCLE TIME in TEST.
FIGURE 14
90-783C
FIGURE 13
ON
1234
2 HOUR
3 HOUR
30 MIN.
1 HOUR
CYCLE PERIOD
90-783C
SET-UP PROCEDURE
CYCLE TIME
TEST
60
MIN.
OFF
0
MIN
MIN.
30
MIN.
(shown set
to 1 hour)
FIGURE 15
4321
ON
VENT-TIMED
HVAC FAN
SYSTEM SETUP
ON
MODEL 70
CONVERTIBLE
HVAC FAN
WHL HOUSE
VENT-AUTO
MODEL 70
OFF
90-969
(shown set to
30 minutes)
VENTILATION / FAN CYCLING SETTINGS
The Aprilaire Dehumidifier has the option
to monitor HVAC heating, cooling and fan
calls to assure the HVAC fan has
operated a predetermined amount of
time each 1/2, 1, 2 or 3 hours. The
dehumidifier can also open a normally
closed damper in an outdoor air intake to
ventilate during this predetermined
amount of time. This feature will
function even if the dehumidifier is
turned off at the dehumidifier or Model
70 Occupied Space Control. The only way
to disable this feature is by turning the
Cycle Time setting to OFF or turning
power off at the On/Off switch.
HVAC EQUIPMENTTHERMOSTAT
WIRE NUT
DEHUMIDIFIER
CONTROL
24 VAC
(10 VA min)
TRANSFORMER
DAMPER
VENTILATION
OPTIONAL
G
R
C
G
W
YY
W
C
R
A+BDEH
REMOTEHVAC EQUIP.
VENT Cf Gs Gh W -YRf
DAMPERS
OPTIONAL OUTDOOR
TEMPERATURE SENSOR
(Model 8052)
SENSOR
ODT
SWITCH
FLOAT
FIGURE 12
90-968

11
VENTILATION / FAN CYCLING SETTINGS (CONTINUED)
• An Aprilaire®Normally-Closed Damper (Model 6506) should
be installed in the outside air intake. It should be wired to the
terminals labeled “VENT DAMPER” on the dehumidifier
control board. Follow all installation instructions supplied
with the damper. Refer to each installation for ducting.
• The Outdoor Temperature Sensor (Model 4278) should be
installed outside in a shaded location (Figure 16) or in an
outside air intake duct, but no more than 3 feet from the
outside (Figure 17).
• The Outdoor Temperature Sensor is not affected by wire
length. However, do not route the wire alongside wires
carrying high voltage (115 VAC or greater), as interference
may occur.
• Connect the wires from the sensor to the terminals labeled “ODT SENSOR” on the dehumidifier.
See Figure 12 for terminal locations.
This installed option allows outside air to be combined with
the fan cycling feature from the dehumidifier, provided the
outside air temperature is in the acceptable range (0-100°F).
Note: The dehumidifier can control the HVAC fan to provide
fan cycling, regardless of whether or not an outdoor
ventilation duct is installed.
NORTH, EAST
OR WEST SIDE
OF BUILDING
OUTDOOR
TEMPERATURE
SENSOR
SENSOR
SENSOR
BRACKET
ABOVE EXPECTED
SNOW LINE
OUTDOOR
TEMPERATURE SENSOR
LEADS
36" MAX.
CENTER LINE
OUTSIDE WALL
B2202617-D
B2202617-E
FIGURE 16
FIGURE 17
VENTILATION GUIDELINES
NOTE: Installer must refer to ASHRAE Standard 62.1-2004 and local building codes to determine ventilation rate. Ventilation
rate is determined by building type and occupancy. Outdoor air ventilation may not be required if an air handler is already serving
this purpose.
O.A. Ventilation = Required Ventilation Rate (CFM/person) x Occupancy (# of people)
Cycle Time Setting = Cycle Period Setting (hours) x 60 min x O.A. Ventilation (CFM)
hour Air Handler Fan Delivery (CFM)
FLOAT SWITCH
If the Model 1720 is installed above a ceiling, the unit should be
placed in a drain pan with a normally closed condensate overflow
safety switch (also known as a float switch). The float switch
should be wired to the float switch terminals on the dehumidifier
control board. See Figure 18. Remove the jumper at the float
switch terminals. The compressor is disabled when the float
switch is open. The Model 1720 will continue to ventilate when
the float switch is open.
CLOSED FLOAT SWITCH
LOW VOLTAGE NORMALLY
FLOAT
SWITCH SENSOR
ODT
90-968A
FIGURE 18

12
DIP SWITCH DEFINITIONS
MODEL 70 – OFF/ON (SYSTEM SETUP SWITCH #1):
HVAC FAN – OFF/ON (SYSTEM SETUP SWITCH #2):
WHL BUILDING / CONVERTIBLE
(SYSTEM SETUP SWITCH #3):
VENT-AUTO / VENT-TIMED (SYSTEM SETUP SWITCH #4):
Determines use of internal RH and temperature sensor or use
of the RH and temperature sensor on the Occupied Space
Control (Model 70).
MODEL 70-OFF. Uses internal RH and temperature sensor.
MODEL 70-ON. Uses Occupied Space Control (Model 70)
RH and Temperature Sensor.
Default is MODEL 70-OFF.
Determines if the HVAC fan activates during a call for
dehumidification.
HVAC FAN-OFF position. The dehumidifier will not activate
the HVAC fan during a call for dehumidification; it will
however activate the HVAC fan for air cycling and ventilation.
HVAC FAN-ON position. The dehumidifier will activate the
HVAC fan during a call for dehumidification as well as for air
cycling and ventilation.
Default is HVAC FAN-OFF.
Determines if ventilation is restricted based on outdoor
temperature.
VENT-AUTO position. The dehumidifier will measure the
outdoor temperature (through sensor, part # 8052) to
determine if the ventilation damper will open. If the outside
temperature is above 100°F or below 0°F the dehumidifier
will not actuate the ventilation damper terminals (VENT
DAMPER). If the outside temperature is between 0°F – 20°F,
the dehumidifier will only actuate the ventilation damper
terminals (VENT DAMPER) when the HVAC system is making
a call for heat. The dehumidifier will energize the HVAC fan
whether or not the ventilation damper opens.
VENT-TIMED position. The dehumidifier will actuate the
ventilation damper terminals (VENT DAMPER) regardless of
the outdoor temperature.
The default position is VENT-AUTO.
Determines when the dampers are powered open or closed.
CONVERTIBLE position. The damper (DEH) terminals are
actuated when the HVAC equipment is making a call for heat,
cool or fan and the dehumidifier is making an internal blower
call for air sampling or dehumidification.
WHL HOUSE position. The damper (DEH) terminals are
actuated any time the dehumidifier is making an internal
blower call for air sampling or dehumidification.
The default position is WHL HOUSE.

13
ADJUSTING THE DEHUMIDIFIER SET POINT
Use the main control knob (Figure 19)
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 dry” will make conditions drier.
Moving the knob toward “less dry”
allows for higher moisture levels.
Setting Dewpoint Set Point (°F)
165
260
356
452
548
644
740
SYSTEM CHECKOUT
SYSTEM SETUP
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 of debris annually. Flush it with water under pressure to
ensure opening is clear.
Note: The drain trap needs to be primed with water prior to unit operation. The drain trap needs to be primed with water prior
to start-up and after extended periods of unit shutdown (winter months).
MAINTENANCE
1. Check the wiring to the HVAC equipment.
2. Rotate the main control knob clockwise to the “TEST” position.
3. If all is set up properly, the dehumidifier blower will turn on.
The compressor will turn on after the dehumidifier blower
has run for 30 seconds. After 1 minute the dehumidifier
blower and compressor will shut off (“TEST” mode only).
4. If the dehumidifier blower does not activate in TEST mode,
refer to the Troubleshooting Guide.
5. For ventilation (optional) test, be sure that 24 VAC is applied
in series with the Aprilaire®Normally-Closed Damper
(Model 6506) and connected to the “VENT DAMPER”
terminals on the dehumidifier control.
6. Rotate the “CYCLE TIME” potentiometer clockwise to the
“TEST” position.
7. If all is set up properly, the HVAC blower will turn on and the
ventilation damper will open. Both should be audible to the
installer. The HVAC blower will remain on and the ventilation
damper will remain open for 1 minute or until the dial is
turned from the “TEST” position, whichever happens first.
8. If the optional ventilation damper or HVAC blower does not
activate in TEST mode, refer to the Troubleshooting Guide.
90-782
FIGURE 19

14
The fan turns on unexpectedly. • The control will turn on the fan as needed to meet the air cycling requirements
determined by the cycle time and cycle period settings.
The compressor never runs. • If a float switch is not installed, confirm that the jumper is installed at the
float switch terminals on the control board.
• If a float switch is installed, confirm that the float switch is not open.
• Control knob is set too low. Increase towards “MORE DRY”.
TROUBLESHOOTING GUIDE
SYMPTOM TROUBLESHOOTING PROCEDURE / POSSIBLE REASON
Dehumidifier is not
draining properly.
• Check condensate trap to be sure it is clear of debris.
• Check drain line for continuous slope, air pockets, etc.
• Confirm trap is properly installed and primed.
Dehumidifier is producing
hot air.
• Reheat of outgoing air will cause a temperature increase across the dehumidifier.
• Unit will possibly run continuously initially. After unit has “dried” building,
dehumidifier will cycle, reducing load.
HVAC fan does not turn
on when cycle time dial is
in “TEST” mode.
• Make sure there is power to the HVAC equipment.
• Check the wiring diagram for the R, C, W, Y, GH, and GS at the HVAC equipment,
thermostat, and the dehumidifier.
• Make sure the sensor is connected to the Outdoor Temperature Sensor terminals or
the System Setup block is set to “TIMED” mode.
• Check the voltage across the R and C terminals at the dehumidifier. Voltage should
be 18 VAC minimum - 30 VAC maximum.
• In “TEST” Mode, the HVAC fan will activate for 1 minute, DO NOT LEAVE IN TEST
MODE AS DEHUMIDIFIER WILL NOT OPERATE.
Dehumidifier Blower is running,
but no airflow.
• Normally Open Damper was used instead of Normally Closed Damper in backflow.
• Total HVAC system static is significantly higher than 1.5” w.c.
Dehumidifier not adequately
dehumidifying.
• Unit will need time to “dry” materials in building before effectively changing RH.
• Too little or too much airflow through dehumidifier.
• Total HVAC system static is significantly higher than 1.5” w.c.
• Compressor is not turning on.
• System undercharged.
The dehumidifier damper does
not open in “TEST” Mode.
• Follow all of the system checkout procedures.
• Check the wiring diagram for the damper and 24 VAC transformers.
Fan cycling operates
continuously after the dial
is taken off “TEST” mode.
• If the HVAC equipment is making a Heat or Cool call, or the fan is in Continuous
Operation, fan cycling will remain on until the requirement set by the cycle period
dip switch and knob is met.
• If the interval is set at 1 HOUR and the cycle time is set at 60 minutes, fan cycling
will be on continuously. Change the setting to a lower amount if this is not desired.
The dehumidifier does not run. • Follow all of the system checkout procedures.
• Check that the power switch on the dehumidifier is on.
• Check that the circuit breaker is not tripped. The dehumidifier requires a minimum
of 14 amps. The dehumidifier should be placed on its own dedicated 20 amp circuit.

• The damper will not open if the cycle time within the
current period has already been met. For instance if
the cycle time is set to 5 minutes and the control has
already ventilated for 5 minutes in that interval, the
damper will remain closed.
• If using the Outdoor Temperature Sensor, check that it
is installed in the Outdoor Air Intake a maximum of 3
feet from the outside, or on the North, East or West
side of the building. (Not in direct sunlight.)
• If the outdoor temperature is below 0°F or above
100°F, the damper will remain closed.
• Verify that the Outdoor Temperature Sensor is
reporting an accurate resistance. Remove the Outdoor
Temperature Sensor leads from ODT Sensor terminals
and check the resistance. Compare the reading with
the resistance shown in Table 2.
15
TROUBLESHOOTING GUIDE (CONTINUED)
SYMPTOM TROUBLESHOOTING PROCEDURE / POSSIBLE REASON
The ventilation damper
does not open when the
HVAC fan is active.
DEHUMIDIFIER SEQUENCE OF OPERATION
IF THE DEHUMIDIFIER IS NOT WIRED TO THE HVAC EQUIPMENT, THE DEHUMIDIFIER WILL SAMPLE AT THE END OF THE
CYCLE PERIOD.
With 3 minutes left in the Cycle Period, the dehumidifier will turn on the dehumidifier blower for 2 minutes. During this time the
temperature and relative humidity are measured and the dewpoint is calculated. If the dewpoint is higher than the setting at the
Control Knob then the dehumidifier compressor will turn on and the dehumidifier will run until it reaches set point.
After reaching the set point, the dehumidifier will not sample again until the end of the next Sample Period.
For example, if the Sample Period is set for 1 hour, the dehumidifier will sample at the end of the hour. Once the dehumidifier
reaches set point and shuts off, the dehumidifier will not sample again until the end of the next hour.
IF THE DEHUMIDIFIER IS WIRED INTO THE HVAC EQUIPMENT, THE DEHUMIDIFIER WILL SAMPLE THE FIRST TIME THE HVAC
EQUIPMENT RUNS IN THE CYCLE PERIOD OR AT THE END OF THE CYCLE PERIOD IF THE HVAC EQUIPMENT DOES NOT RUN.
For example, if the Cycle Period is set to 1 hour and the air conditioner starts 15 minutes into that hour, the dehumidifier will
sample when the air conditioner starts. Once the dehumidifier begins dehumidifying, it will run until set point is reached. If the
dehumidifier samples and determines that dehumidification is not needed, it will not sample again until the next Cycle Period.
Outdoor
Temperature
-30˚F
-20˚F
-10˚F
0˚F
10˚F
20˚F
30˚F
40˚F
50˚F
60˚F
70˚F
80˚F
90˚F
100˚F
Resistance
229,500 OHMS
162,500 OHMS
116,500 OHMS
84,500 OHMS
62,000 OHMS
46,000 OHMS
34,500 OHMS
26,000 OHMS
20,000 OHMS
15,500 OHMS
12,000 OHMS
9,500 OHMS
7,500 OHMS
6,000 OHMS
TABLE 2
DAMPER SEQUENCE OF OPERATION
In the Whole Building Convertible to Localized installation 4 motorized dampers are used to control the air flow through the
dehumidifier. The dampers are energized when the HVAC equipment is running. This means that when the HVAC equipment
is running, the dampers are in the Whole-Building position. When the HVAC equipment is not running, the dampers are in the
local position.

© 2005 RESEARCH PRODUCTS CORPORATION
P.O. BOX 1467 • MADISON, WI 53701-1467 • PHONE: [phone] • FAX: [phone] • www.aprilairecontractor.com
61000407 11.05
B2203961A
LIMITED WARRANTY
Your Research Products Corporation Aprilaire®Dehumidifier is expressly warranted for two (2) year from date of installation to be free from defects.
Research Products Corporation’s exclusive obligation under this warranty shall be to supply, without charge, a replacement for any component which is found
to be defective within two (2) year period and which is returned not later than thirty (30) days after said two (2) year period by you to either your original
supplier or to Research Products Corporation, Madison, Wisconsin 53701, together with the installation date of the dehumidifier.
THIS WARRANTY SHALL NOT OBLIGATE RESEARCH PRODUCTS CORPORATION FOR ANY LABOR COSTS AND SHALL NOT APPLY TO DEFECTS IN
WORKMANSHIP OR MATERIALS FURNISHED BY YOUR INSTALLER AS CONTRASTED TO DEFECTS IN THE DEHUMIDIFIER ITSELF.
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE SHALL BE LIMITED IN DURATION TO THE AFORESAID TWO YEAR
PERIOD. RESEARCH PRODUCTS CORPORATION’S LIABILITY FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES, OTHER THAN DAMAGES FOR PERSONAL
INJURIES, RESULTING FROM ANY BREACH OF THE AFORESAID IMPLIED WARRANTIES OR THE ABOVE LIMITED WARRANTY IS EXPRESSLY EXCLUDED. THIS
LIMITED WARRANTY IS VOID IF DEFECT(S) RESULT FROM FAILURE TO HAVE THIS UNIT INSTALLED BY A QUALIFIED HEATING AND AIR CONDITIONING
CONTRACTOR. IF THE LIMITED WARRANTY IS VOID DUE TO FAILURE TO USE A QUALIFIED CONTRACTOR, ALL DISCLAIMERS OF IMPLIED WARRANTIES SHALL
BE EFFECTIVE UPON INSTALLATION.
Some states do not allow limitations on how long an implied warranty lasts or the exclusion or limitation of incidental or consequential damages so the above
exclusion or limitations may not apply to you.
This warranty gives you specific legal rights and you may also have other rights which vary from state to state.
VENTILATION OR FAN CYCLING SEQUENCE OF OPERATION
If the dehumidifier is providing outdoor air ventilation or fan cycling, it is monitoring the HVAC equipment to provide the amount
of HVAC fan run time that has been set by the Cycle Time during the Cycle Period.
If an outdoor air damper has not been installed then the dehumidifier is providing fan cycling. The dehumidifier will monitor the
HVAC system and if the system has not run for the specified Cycle Time within the Cycle Period, the dehumidifier will energize
the HVAC fan through the G terminal to provide the desired amount of fan run time.
For example, if the Cycle Time is set for 10 minutes and the Cycle Period is set for 1 hour then the dehumidifier will provide
10 minutes of fan cycling or outdoor air ventilation. If the HVAC system runs for 5 minutes during this hour then the dehumidifier
will energize the fan for an additional 5 minutes.
If an outdoor air damper has been installed, then the Model 1720 is providing outdoor air ventilation. The 1720 will open the
outdoor air damper whenever the HVAC system is running, up to the amount of time specified by the Cycle Time. The
dehumidifier will energize the HVAC fan and open the outdoor air damper to provide the desired ventilation time if the HVAC
system has not run for the specified Cycle Time.
If an Outdoor Temperature Sensor has been installed, then the dehumidifier will use the outdoor temperature to determine if the
outdoor air damper is to be opened. If the outdoor temperature is above 100°F the damper will not open. If the temperature is
between 20°F and 0°F the damper will only open with a heat call. If the outdoor temperature is below 0°F, the damper will not
open. If the Outdoor Temperature Sensor is not installed then the temperature is not considered in opening the damper.
Your Warranty Registration information will not be sold or shared outside of this company.
Thank you!
WARRANTY REGISTRATION
Please… Take a few minutes to visit us on-line at www.aprilaire.com to register your Aprilaire product.
If you do not have on-line access, please mail a postcard with your name, address, phone number, product purchased and date of purchase to:
Research Products Corporation
P.O. BOX 1828
Madison, WI 53701