Installation manual

035-16682-000-E-0303
Unitary Products Group 73
Damper). As long as the building pressure floats within
the null range, neither contact is closed and ACT2 holds
the damper in position. When ACT2 opens more than 5
an end switch (ACT2-1) closes to power the 10M starter
and engage the power exhaust fan motor. When the
power exhaust is disabled, ACT2's spring return closes
the exhaust dampers and 10M opens to shut down the
exhaust fans.
12. Power Exhaust Option with Variable Frequency Drive:
The power exhaust controls are powered through relay
MR (supply air Motor Relay) with a call for the supply
fan. Once powered, the sensor BSP (Building Static
Pressure sensor) sends a signal to terminal 53 of the
VFD. Contact closure of PR (Power Exhaust Relay)
gives the VFD permission to run.
13. Non-modulating Power Exhaust Option: The power
exhaust controls are powered on a call for the supply
fan. Switch SSP1 (Switch Static Pressure - Building)
closes whenever the building pressure exceeds setpoint.
If the exhaust motor has been off for a minimum of five
minutes, TDR (Time Delay Relay - five min. Anti-Short -
Cycle Timer) power is applied to the 10M starter to
engage the power exhaust fan motor. The outlet pres-
sure of the power exhaust fan forces the barometric
relief dampers open. Exhaust fan operation is continued
until the building static pressure falls below the SSP1
setpoint or until the supply fan call is satisfied. Gravity
closes the barometric relief dampers when the exhaust
fans are off.
VARIABLE AIR VOLUME UNIT (VFD & IGV)
OVERVIEW
The VAV units operate in one of three modes: Night Mode,
Warm-up Mode, and Day Mode. The unit operational mode is
determined by the status of a field supplied contact that
switches between the Day and Night Modes. Day Mode oper-
ation is further segregated into a Warm-up Mode and a Cool-
ing mode, depending upon the return air temperature. On all
VAV units, heating i
s not available during the day or set-
up mode. Heating is
available in the night set back or
morning warm-up mode.
The bypass VFD is a standard Variable Frequency
Drive packaged with a set of contactors. When the
bypass mode is activated, contactors on both the
line side and the load side of the VFD open, isolat-
ing the VFD. At the same time, a contactor con-
nects the indoor fan motor direct to supply voltage,
if the motor operation is being called for by the
controls. At this point the motor will go to full RPM
and there is a potential for over pressuring the
ducts.
The air balancer must set CFM to stay within a
static pressure that the ductwork can tolerate
when the motor is at full RPM, whether the VAV
boxes are full open, or with non-VAV ductwork.
If the duct system includes VAV boxes, they
must be driven open in the same manner as
going to heat mode. The drive indicates being
in ‘bypass’ mode with normally open contacts
wired to terminal block 1, position 6 and 7.
Voltage sufficient to signal the boxes to open
must be wired through this contact. This is a
field-install connection.
York cannot be responsible for damage to duct-
work or other affected items if running the motor at
full RPM overpressures the system.
Electrical diagrams for the extra circuitry of the
bypass are included with the VFD information
packed in the unit.