Oil Sump Temperature Control
The oil sump temperature cont rol is regulate d by the PIC which uses th e oil heater relay
when the machine is shut do wn.
As part of the pre-start checks executed by the controls, oil sump temp erature is co mpared
against evaporator ref rigerant temperat ure. If the differenc e bet ween these 2 temperat ur e s is
50 F (27.8 C) or less, the sta r t-u p will be delayed until the oil temperature is 50 F (27.8 C) or
more. Once this tempera ture is confirmed, the start-up continues.
The oil heater relay is ene rgized whenever the chi ller compressor is off and the oil sump
temperature is less than 150 F (65.6 C) or the oil sum p te mperature is less than the cooler
refrigerant tempera ture plus 70° F (39° C). The oil heater is turned off whe n the oil sump
temperature is eithe r 1) mo r e th an 160 F (71.1 C); or 2) the oi l s um p t emperature is more tha n
155 F (68.3 C) and more than the cooler refrigerant temp erature plus 75° F (41. 6° C). The oil
heater is always off duri ng start-up or when the com p ressor is running.
When a power failure to th e P S IO m odu le has occurred for more t han 3 hours (i.e., initia l
start-up), the c ompressor guid e vane opening will be slow ed down to pr event excessive oil
foaming that ma y result from refrigerant mi gration into t he oil sump during the powe r failure.
The vane opening will be s low ed to a value of 2° F (1.1° C) pe r minute with temperat ur e ramp
loading.