Variable Frequency Drive (VFD)
An optional VFD may be
installed at the factory for
purposes of controlling the
speed of the blower motors.
Its purpose is to constantly
regulate the speed of the
blower motor, in response
to various optional sensors.
When the VFD receives a
predetermined signal, it will
adjust the frequency (hertz)
of the AC power supply to
any connected motor, thus
changing the speed of rotation.
The VFD is preset at the factory to respond to
conditions specified by the owner. In some cases,
the VFD will be controlled by owner-installed sensors
and controlling devices such as CO2 sensors,
dehumidistats or pressure sensors.
Refer to the VFD manufacturer’s information and unit-
specific wiring diagram supplied with the unit. For
additional downloadable documentation regarding
the VFD installed in this unit, visit the manufacturer’s
website.
Phase Monitor
A phase monitor constantly
checks for loss of a phase, phase
unbalance or phase reversal. It
requires 24 VAC to operate. When
a fault is detected, it cuts off the
power supply to the low voltage
terminal strip, disabling all motors.
It has two LED indicator lights,
showing “on” and “fault”.
Typical Variable
Frequency Drive (VFD)
Refer to unit-specific
documentation.
Phase Monitor
13
Model MPX Make-Up Air Unit
Model XMPX Make-Up Air Unit
