Controls - 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. When compressor time delay (5±2
minutes) is completed, 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.
When compressor time delay (5±2 minutes) is completed, a
circuit is made to C, starting COMP and OFM. Circuit R-G
26
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;
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.
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.