Aprilaire 8120 Safety & Installation Instructions page 5

STEP 9: SET THE SAMPLING TIME INTERVAL
A. The Cycle Time Interval is the time period over which ventilation
will occur. This is variable from 1 to 4 hours depending on
customer preference. Keep in mind, once the Ventilation
requirement is met the Vent Control won't run again until the
start of the next cycle. The Cycle Time is the length of the
sampling period, while the Ventilation time as set is the actual
operating time.
B. The device is factory set to a 1 hour sample time. This is
recommended for a quicker reaction to conditions. Also the
longer Cycle Intervals are more likely to require more than the
60 minutes available on the dial.
C. Remove knob by carefully pulling it out from the case. Snap the
cover off and refer to Figure 7 to locate the cycle time setting
tab and pins.
D. The jumper tab on the 5 pin array determines the sampling time
interval. Per diagram this can be 1,2,3 or 4 hours. The jumper
tab is removed by pulling it straight out from the pins. Take care
in replacing, do not bend.
STEP 10: DETERMINE THE VENT CONTROL KNOB SETTING
A. The run time in minutes is set with the knob. The Time 0 setting keeps the circuit live but the
vent won't operate. OFF deactivates it completely. Any setting made is the total running
time per 1, 2, 3 or 4 hour cycle.
B. Record your entries from Steps 7C and 8C in the Table on page 6. From this you can determine
the correct knob setting. For example, if 80 CFM is required but the Vent delivers 120 CFM set
the knob to 40 minutes. The knob settings as listed are for a 1 hour cycle time.
C. All values can be set except those in the black area. If the Vent Control is clocked out (black
area) and if the cycle is set to 2, 3 or 4 hours, reset the pin jumper to get a settable time. For
example, if 80 minutes is required at 2 hours, at 1 hour this would be a settable 40 minutes. If
you're still clocked out or are already set to a 1 hour cycle consult with the homeowner about
installing a second device.
FIGURE 7 – Cycle Time
CYCLE TIME
1 HR 3 HR
2 HR 4 HR
5
WIRING AND
CYCLE TIME
JUMPER
1 HR 3 HR
CONFIGURATION
2 HR 4 HR
G
TO STAT
S
C R D D T T
G
H TO HVAC
W
TO HVAC
10005991
OUTDOOR
TEMPERATURE
SENSOR
FIGURE 8 – Set Vent Time
INSTALLATION TEMPLATE
4-11/16" x 2-15/16" cutout
90-698
90-702