Field Controls HHSC+, User Manual, Page: 15 / 20

page 15
ACTIVATION BY THERMOSTAT
The HHSC+ monitors the activity of the thermostat and performs operations as described here. If the
thermostat issues a demand for heating or cooling, or the HVAC fan is manually switched on, before an
HHSC Fan On or Fan Cycle Period time expires (see Independent Operation above), the HHSC+ will
immediately begin a new Fan Cycle period. The HHSC+ will then command the FAD vent damper to open,
and the Auxiliary Output terminals will be appropriately energized, for the Fan On and Vent On times as
stated above. The HVAC fan will also be commanded to run by the HHSC+ if either a cooling demand
occurs, or if the fan is manually switched on at the thermostat.
NOTE: The HHSC+ will not give a command to run the HVAC fan if a demand for heating only occurs.
The HVAC system will operate the fan independently when this occurs. This is also true when there is
a demand for cooling, but the HHSC+ merely transmits the fan on command which is issued by the
thermostat.
If the thermostat becomes satisfied and terminates the command for heating or cooling, or the fan is
manually switched to Off or Auto while there is no current demand for heating or cooling, the HHSC Fan
ON and Vent On times will be cut off, and the HHSC+ will terminate the commands to the FAD damper,
the HVAC fan, and the Auxiliary Output. The HHSC+ will then remain idle for the remainder of the Fan
Cycle Period, when it will begin a new cycle, or the system thermostat calls for new HVAC action.
ACTIVATION BY REMOTE (OVERRIDE) DEVICE(S)
Remote device(s) having dry contacts, such as simple wall switches, timers, CO alarm contacts, pressure
switches etc. may be used for remote activation of the HHSC+ ventilation system. Multiple such devices
may be connected to the AUX-IN and R terminals in parallel (see Fig. 4); if any of these devices complete
an electrical connection between R and AUX-IN, the HHSC+ will activate the HVAC fan, open the FAD
damper, and activate the Auxiliary Out terminals, for as long as any of the remote devices are closed.
NOTE: Do not directly connect any devices having solely electronic means of switching electrical current
(transistor or triac switching), such as many current sensing relays; electrical leakage through such devices
may cause improper operation of the system and may damage the HHSC+ and/or other remote devices. If
such a device is to be used, install an isolation relay between the HHSC+ and the device.
POWER OUTAGE
If a power outage occurs, the HHSC+ will resume normal operation after about 15 seconds after power is
restored, with all settings as they were prior to the outage, and will display the correct time and date. The
display and LED will not show or be illuminated, but the internal backup battery will continue to maintain the
time, date, and filter and UV lamp replacement timers; no corrections are required. Battery life is in excess
of one year under such conditions.