Reznor YDSA Unit Installation Manual - Manual (Page 31)

Form I-Y, P/N 273646R6, Page 31
7.6 Supply Fan
with Variable
Frequency
Drive
Variable Frequency Drive
The supply fan is a plenum fan with backward curve blades and a premium efficiency
inverter rated motor. All units are equipped with variable frequency drive. With variable
frequency drive control, the supply fan will operate on varying speeds as determined
by the electrical frequency.
Depending on which control (Option VFC) was selected, the variable frequency drive
is controlled by duct pressure, building pressure, or constant volume speed settings.
See control information in Paragraph 8.2.
Generally, high speed is used for cooling and low speed for heating. Maximum allow-
able temperature rise for a gas heat section is 100°F Model YDMA, 70°F for Model
YDHA, or 50°F for Model YDSA.
The VFD is set according to the order specifications. If changes are required, follow the
ABB instructions provided to program the settings.
Setting Fan CFM During startup, the CFM will need to be checked for the supply fan and an optional
exhaust fan. Follow the instructions in Paragraph 10.3 to use the unit interface TAB
Menu and the airflow / pressure drop chart on pages 69 thru 73 to determine the airflow
settings.
7.7 Condenser Fan
Motors and Fans
Condenser fan motors are direct-drive, statically and dynamically balanced, and per-
manently lubricated. Condenser fan motors are either open drip proof motors with
external sling protection against water penetration or high efficiency ECM motors with
speed control (Option CUF4). All motors have auto reset thermal overload protection.
Area above the fans should always be unrestricted and open.
Condenser Fan Control
The unit has a maximum of four condenser fans.
If ordered with low ambient control (Option BE8), depending on type of condenser fan,
the low ambient controller will change the speed of the fan to regulate the head pres-
sure.
7.8 Compressors All of the compressors are high efficiency hermetic scroll type designed for use with
R-410A refrigerant.
Compressor Amps/
Voltage
(For additional information,
refer to the Operation/
Maintenance/Service
Manual, Form O-Y.)
Mechanical Compressor Protection - A low pressure cutoff (LPCO) switch is used for
protection against compressor damage due to a loss of system charge. This protection
prevents short cycling on the internal overload (IOL) which can pump the oil out of the
compressor.
All compressors also have manual reset high pressure cutouts (HPCO) and frost stats.
Crankcase Heaters - Each compressor has a band-type crankcase heater. Crank-
case heaters must always be energized for at least 24 hours prior to operating
the compressor.
Compressor Modulation - These units have scroll compressors equipped with modu-
lating valves and a digital controller that interfaces the compressor with the system
controller. Compressor operation will start based upon a call for cooling and will modu-
late to maintain the discharge air temperature setpoint. There is a five-minute compres-
sor on/off time.
Compressor Staging - Each system leaves the factory with the compressor staging
sequence set. The compressor will start based upon a call for cooling to maintain the
discharge air temperature setpoint. There is a minimum 300 second ON and OFF time
for each stage (not compressor).
For additional information about compressor operation, see the Operation/Mainte-
nance/Service Manual, Form O-Y.
Optional Hot Gas Bypass (applies to non-modulating compressors) - If ordered with
Option AUC8, the bypass valve will provide expanded compressor modulation at low
outside air temperatures by allowing some of the gas from the suction line to be re-