Johnson Controls DSV60B-300B, Installation Instructions Manual

Page: 10 / 48

FORM 145.29-IOM2 (814)
10
JOHNSON CONTROLS
Refer to separate ‘VFD Installation and Operation
Manual’ for detailed installation and operation
instructions.
Do not run evaporator fan motor
below 30Hz otherwise coil freeze-up
and nuisance lock-outs may occur.
Building
excessive ductwork
pressure can cause damage to unit
or personnel
VFD Input/Output
Note: Jumper is required between contacts 10 & 11
HOT GAS BYPASS (HGBP)
Optional HGBP on the lead compressor circuit (circuit
#1) meters flow of compressor discharge hot gas to
the system low side in order to balance the system
capacity to the space load requirement. HGBP is
factory installed using an adjustable hot gas regulator.
The bypassed hot gas from the compressor is
discharged to the evaporator inlet (i.e.: between the
TX valve and distributor) via a Tee connection.
Adjusting HGBP set point
The desired coil suction pressure or coil temperature
when the HGBP valve opens is selectable by
adjusting the screw on the HGBP valve. To set the
load run the unit and cool down the evaporator coil by
either shutting the fans or by blocking the airflow until
the suction pressure drops at least 5psi below the
desired evaporator coil setpoint. The next step is to
allow the pressure to be raised by the bypassed gas,
the screw spring adjustment can be set until the
HGBP valve closes at the desired set point.
The pressure of the evaporator coil is set to maintain
an evaporator coil temperature above the point where
frost and coil freeze up could form.
AIR SIDE ECONOMIZER
Optional air side economizer mixing box is designed
to attach the return air side of the evaporator. Mixing
comes with low-leakage opposed blade dampers.
Economizer is used to provide ventilation and free
cooling for the JCI DSV series of vertical air handlers.
Economizer setup is done through the LCD keypad
display locating on the economizer control module
mounted on the mixing box. Access to the mixing box
is required.
The factory supplied economizer includes:
economizer module, mixing box, actuator, enthalpy
sensor, temperature sensor, dampers, and wiring
harness. Refer to Appendix C for economizer
electrical wiring schematics.
SEQUENCE OF OPERATION
High enthalpy sequence
Enthalpy sensor should be located in the outdoor air
duct. When the outside air enthalpy exceeds the
enthalpy set-point, the economizer module Y1-In and
Y1-Out terminals are closed and economizer will be
forced into the minimum damper position setting. The
DSV unit’s microprocessor board will control
mechanical cooling requirements.
Low enthalpy sequence
When the outside air enthalpy is below the enthalpy
set-point, economizer module Y1-In and Y1-Out
terminals are opened and free cooling is activated.
The JCI unit’s microprocessor board turns off
compressor operation.
Damper Modulation
The temperature sensor should be located in the
supply discharge air duct. Locating the sensor in the
discharge air provides effective 'low-limit' sensing and
control. The outside-air damper remains at minimum
position if the discharge air temperature is below 50
0 F
or 10
0
C. If the discharge air temperature is between
50
0
to 56
0
F (10
0
to 13.3
0
C) the outside air damper
will modulate between minimum position and fully
open. Above 56
0 F (13.3 0 C) the outside air damper
will remain in the fully open position.
Jumper set
to 4-20mA
4-20mA Output from
Transducer (
–COM)
Transducer
Power (+EXC)
24VDC