Carrier 17/19EX - Manual (Page 56)

Hot Gas Bypass Contactor Relay (3C) (Optional)
This relay, located in the power panel, controls the opening of the hot gas bypass valve. The
PIC energizes the relay during low load, high lift conditions.
Oil Auxiliary Relay (4C)
This relay, supplied only with open-drive machines, opens the oil cooler solenoid valve and
interlocks the oil pump with the compressor.
Control Transformers (T1-T4)
These transformers are located in the power panel and convert incoming control voltage to
either 21 vac power for the PSIO module and options modules, or 24 vac power for 3 power
panel contactor relays and a control solenoid valve.
Control and Oil Heater Voltage Selector (S1)
It is necessary to use 115 v incoming control power in the power panel. The switch must be
set to the 115-v position.
Oil Differential Pressure/Power Supply Module
This module, which is located in the control center, provides 5 vdc power for the transducers
and LID backlight.
On open-drive machines, this module outputs the difference between two pressure
transducer input signals. The module subtracts oil supply pressure from transmission sump