Trane RAUC-C60 Low Ambient Dampers, Compressor Crankcase Heaters, Pump Down, System Start-Up

System Start-Up

Figure 43. Condenser Fan Locations

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.

86 SS-SVX09A-EN