Carrier 17/19EX - Manual (Page 85)

Oil Sump Temperature Control
The oil sump temperature control is regulated by the PIC which uses the oil heater relay
when the machine is shut down.
As part of the pre-start checks executed by the controls, oil sump temperature is compared
against evaporator refrigerant temperature. If the difference between these 2 temperatures is
50 F (27.8 C) or less, the start-up will be delayed until the oil temperature is 50 F (27.8 C) or
more. Once this temperature is confirmed, the start-up continues.
The oil heater relay is energized whenever the chiller compressor is off and the oil sump
temperature is less than 150 F (65.6 C) or the oil sump temperature is less than the cooler
refrigerant temperature plus 70° F (39° C). The oil heater is turned off when the oil sump
temperature is either 1) more than 160 F (71.1 C); or 2) the oil sump temperature is more than
155 F (68.3 C) and more than the cooler refrigerant temperature plus 75° F (41.6° C). The oil
heater is always off during start-up or when the compressor is running.
When a power failure to the PSIO module has occurred for more than 3 hours (i.e., initial
start-up), the compressor guide vane opening will be slowed down to prevent excessive oil
foaming that may result from refrigerant migration into the oil sump during the power failure.
The vane opening will be slowed to a value of 2° F (1.1° C) per minute with temperature ramp
loading.