Controls; Sequence Of Operation - Carrier 50JZ 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
sec 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-sec delay†.
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;
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motors and heaters deenergize. The IFM is controlled by a
time-delay relay that keeps the fan on for 60 sec†.
Defrost — Defrost board (DB) is a time and temperature
control, which includes a field-selectable time period (Dip
switch 1 and 2 on the board) between checks for defrost (30,
60, 90, or 120 minutes). Electronic timer and defrost cycle
start only when contactor is energized and defrost thermostat
(DFT) is closed.
The defrost board is also equipped with a 3rd dip switch for
selecting Quiet Shift operation. The Quiet Shift operation
turns compressor off at defrost initiation and termination.
Unit is factory shipped with quiet shift turned off.
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.† Standard PSC indoor motor.
2. Compressor time delay occurs through the defrost control
board.
3. 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.
4. ICM FIOP models only—The indoor blower operation
with a call for fan operation (G) in either cooling or heat
pump heating (compressor) modes will perform by the on/
off delay profile selected at start up on the easy select™
board.