Controls - Carrier 50JX Series Product Data

Controls

Sequence of operation
When power is supplied to unit, the transformer (TRAN) is
energized.
On units with crankcase heater, heater is also energized.
Cooling — With the thermostat subbase in the cooling
position, the thermostat makes circuit R-O. This energizes
the reversing valve solenoid (RVS) and places the unit in
standby condition for cooling.
As the space temperature rises, the thermostat makes,
closing circuit R-Y. A circuit is made to contactor (C),
starting the compressor (COMP) and outdoor-fan motor
(OFM). Circuit R-G is made at the same time, energizing the
indoor-fan relay (IFR) and starting the indoor-fan motor
(IFM) after a 1-second delay.
When the thermostat is satisfied, contacts open, deenergizing
C. The COMP and OFM stop, and the IFM stops after a 60
second time delay.
Heating — On a call for heat, thermostat makes circuits
R-Y and R-G.
A circuit is made to C, starting COMP and OFM. Circuit R-
G also is completed, energizing IFR and starting IFM after
a 1-second delay.
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Should room temperature continue to fall, circuit R-W is
made through second-stage thermostat bulb. If optional
electric heat package is used, a relay is energized, bringing
on first bank of supplemental electric heat. When thermostat
is satisfied, contacts open, deenergizing contactor and relay;
motors and heaters deenergize. The IFM is controlled by a
time-delay relay that keeps the fan on for 60 seconds.
Defrost — Defrost board (DB) is a time and temperature
control, which includes a field-selectable time period
between checks for defrost (30, 50, and 90 minutes).
Electronic timer and defrost cycle start only when contactor
is energized and defrost thermostat (DFT) is closed.
Defrost mode is identical to cooling mode, except outdoor
fan motor stops and a bank of optional electric heat turns on
to warm air supplying the conditioned space.
NOTES:
1. Compressor time delay occurs through the defrost control
board.
2. Defrost control board has built in 5 minute compressor
delay: once the compressor has started and then stopped, it
cannot be restarted again until 5 minutes have elapsed.