YORK INTERNATIONAL
78
Sequence of Operation
FORM 100.50-NOM1 (604)
• Applications uses two return air fans each with
there own motor being controlled by a single VFD
drive.
• The return fan VFD drive is controlled by a pressure
transducer with a static pressure probe located in
the return section of the unit.
• The return fan VFD is programmed to maintain
+0.1 to +0.15 inches of WC of static at the probe.
These values are programmed into the VFD at the
factory. The value can be veri
Þ
ed by checking item
# 204 and 205 in Menu 2 (References and Limits) in
the VFD program. Refer to Installation, Operation
& Maintenance Form 100.40-N04 for additional
information.
• The unit will also require a motorized exhaust air
damper that operates off a building pressure trans-
ducer.
• The supply air VFD is controlled by the duct static
transducer.
• The supply air blower and return air fan will always
be energized together.
• The speed of the indoor blower and the opening of
the exhaust air damper will both in
ß
uence the speed
at which the return air fan operates.
0 – 25% Manual /2 Position Outside Air, VFD
Supply Fan, with No Exhaust
This con
Þ
guration would be used for applications where
the supply fan performance cannot meet the total static
requirement of the duct system. Ventilation air is sup-
plied through the unit but exhaust is handled by other
means. This allows the external static pressure to be split
between the return air and supply air fan while bringing
ventilation air into the building.
• Applications uses two return air fans each with
there own motor being controlled by a single VFD
drive.
• The return fan VFD drive is controlled by a pressure
transducer with a static pressure probe located in
the mixed air return section of the unit.
• The return fan VFD is programmed to maintain -
.03 to -.05 inches of WC static at the probe. These
values are programmed into the VFD at the factory.
The value can be veri
Þ
ed by checking item # 204
and 205 in Menu 2 (References and Limits) in the
VFD program. Refer to Installation, Operation
& Maintenance Form 100.40-N04 for additional
information.
• The supply air VFD is controlled by the duct static
transducer.
• The supply air blower and return air fan will always
be energized together.
• As the pressure in the return air section becomes
more negative the return air fan will speed up. As
the pressure in the return section increases above
the setting the return air fan will slow down.
• The percent of outdoor air will remain the same
regardless of the air
ß
ow through the unit.
0 – 25% Manual /2 Position Outside Air, VFD
Supply Fan, with Motorized Exhaust Damper
This con
Þ
guration would be used for applications where
the supply fan performance cannot meet the total static
requirement of the duct system. Ventilation air is sup-
plied through and exhausted by the unit. This allows the
external static pressure to be split between the return air
and supply air fan while bringing ventilation air into the
building and exhausting return air.
• Applications uses two return air fans each with
there own motor being controlled by a single VFD
drive.
• The return fan VFD drive is controlled using a pres-
sure transducer with a static pressure probe located
in the mixed air return section of the unit.
• The return fan VFD is programmed to maintain -
.03 to -.05 inches of WC static at the probe. These
values are programmed into the VFD at the factory.
The value can be veri
Þ
ed by checking item # 204
and 205 in Menu 2 (References and Limits) in the
VFD program. Refer to Installation, Operation
& Maintenance Form 100.40-N04 for additional
information.
• The unit will also require a motorized exhaust air
damper that operates off a building pressure trans-
ducer.
• The supply air VFD is controlled by the duct static
transducer.
• The supply air blower and return air fan will always
be energized together.
• As the pressure in the return air section becomes
more negative the return air fan will speed up. As
the pressure in the return section increases above
the setting the return air fan will slow down.
• The percent of outdoor air will remain the same
regardless of the air
ß
ow through the unit.
