Of Operations - Aprilaire 1720 Installation,Safety & Maintenance Manual

TROUBLESHOOTING GUIDE
SYMPTOM
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.
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.
(CONTINUED)
TROUBLESHOOTING PROCEDURE / POSSIBLE REASON
• 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.
TABLE 2
Outdoor
Temperature
Resistance
-30˚F 229,500 OHMS
-20˚F 162,500 OHMS
-10˚F 116,500 OHMS
0˚F 84,500 OHMS
10˚F 62,000 OHMS
20˚F 46,000 OHMS
30˚F 34,500 OHMS
40˚F 26,000 OHMS
50˚F 20,000 OHMS
60˚F 15,500 OHMS
70˚F 12,000 OHMS
80˚F 9,500 OHMS
90˚F 7,500 OHMS
100˚F
6,000 OHMS
15