ENVIRO-TEC
28
FORM ET115.24-NOM11 (118)
FAN RELAY BOARD – INSTALLATION, OPERATION AND MAINTENANCE
The Fan Relay Board assembly (FRBii) provides
electronic control for the fan motor and various
connections for peripheral devices. The FRBii accepts
incoming single phase power of nominal AC voltages
120, 208, 240 and 277. The assembly includes a multi-
tap transformer (30VA or 50VA) that steps each of these
primary voltages to 24 VAC. The assembly allows for
the control of a three speed fan motor, including a relay
for control of the neutral voltage signal path.
The FRBii can be connected to an external device (e.g.,
thermostat, controller, 3-speed switch) to control the
three fan speeds. The FRBii includes logic to detect
when multiple speeds are commanded simultaneously
and block all but the highest of the commanded speeds
from being sent to the motor windings. A signal to
call for electric heat from an external controller will
verify that a fan speed is selected before providing the
command signal to the external electric heat control to
ensure that electric heat can only be energized when the
fan motor is operational. The assembly includes factory
provided harnesses to allow for faster installation and
improved troubleshooting by the end user.
The FRBii allows for peripheral devices (e.g., thermostat
controllers, electric heat relays, water valve actuators,
condensate drain pan float switches, air dampers) to be
connected by either the OEM or by the installer. The fan
relay board also includes a fuse on the secondary side
of the transformer to protect against incorrect wiring of
external components, shorting the transformer leads.
The signals in the screw terminal block (TB1) and
18-pin black connector (J1) have a nominal voltage of
24VAC. These signals are properly insulated from line
voltage present on the assembly (J2-J5).
Figure F.1: Fan Relay Board (FRBii)
