86 SS-SVX09A-EN
System Start-Up
Low Ambient Dampers
Low Ambient Dampers are available as a factory installed option or can be field-installed. Dampers
are used to extend the operation of these units from the standard operational temperatures to a
minimum of 0ºF without hot gas bypass or 10ºF with hot gas bypass. (These values apply when
wind speed across the condenser coil is less than 5 m.p.h.). If typical wind speeds are higher than
5 m.p.h., a wind screen around the unit may be required. By restricting the airflow across the
condenser coils, saturated condensing temperatures can be maintained as the ambient
temperatures change.
The low ambient damper actuator controls damper modulation for each refrigerant circuit in
response to saturated condensing temperature.
Compressor Crankcase Heaters
Each compressor is equipped with a crankcase heater and is controlled by a 600 volt auxiliary
switch on the compressor contactor. The proper operation of the crankcase heater is important to
maintain an elevated compressor oil temperature during the “Off” cycle to reduce oil foaming
during compressor starts.
When the compressor starts, the sudden reduction in crankcase pressure causes the liquid
refrigerant to boil rapidly causing the oil to foam. This condition could damage compressor
bearings due to reduced lubrication and could cause compressor mechanical failures.
When power has been “Off” for an extended period, allow the crankcase heater to operate a
minimum of 8 hours before starting the unit.
Pump Down
Each circuit will go into a pump down cycle when the last compressor on that circuit is turned "Off".
During pump down, the solenoid valves are closed, the reset circuit is bypassed and the
compressor will continue to run until the 30 psig pressure switch opens.
Figure 43. Condenser Fan Locations
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