McQuay IM 980-1 15
Operation and Maintenance
Low-Voltage (LV) Interface Board
The low-voltage interface board is used with any remote (wall
mounted) McQuay thermostat or control. It can also be used in
conjunction with a controller of a building automation system
(BAS) control where low voltage is needed to operate the fan
coil. It is located in the control box for the unit (see Figure 11,
page 10).
The LV interface board includes:
• Three 24-volt relays with line-voltage contactors to operate
the fan motor speeds.
• Terminal connections for interfacing to:
• An optional remote-mounted thermostat.
• Low-voltage actuators for heating and cooling valves.
• A return air sensor.
• A pipe temperature sensor for changeover from heating
to cooling on two-pipe systems.
• A factory-wired and installed transformer.
See Figure 18 for a list of connecting points to the board. For
additional wiring information, see the typical wiring diagram
Figure 37, page 28 or the unit’s wiring diagram, which is
attached to the corner panel on cabinet units and to the chassis
front cover on hideaway units. (see Figure 12, page 11).
For instructions on field-mount MT155 thermostats on units
supplied with LV Interface boards (a typical arrangement for a
5-day Quick Ship Program), refer to page 45.
Figure 18: LV Interface Board 24 VAC connections
Low Voltage Fan motor control
Low-voltage valve actuators
Room air or return air temperature sensor
Pipe temperature sensor
Condensate overflow sensor
Remote thermostat 24 VAC power
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