Controls - Carrier Comfort 50EZ-A Product Data

CONTROLS

Operating sequence
When power is supplied to unit, the transformer (TRAN) is
energized.
On units with crankcase heater, heater is also energized.
Cooling — With the thermostat in the cooling position, the
thermostat makes circuit "R" to "O". This energizes the reversing
valve solenoid (RVS) and places the unit in standby condition for
cooling.
As the space temperature rises, the thermostat closes circuit "R" to
"Y". A circuit is made to contactor (C), starting the compressor
(COMP) and outdoor- -fan motor (OFM). Circuit "R" to "G" is
made at the same time and starts the indoor- -fan motor (IFM).
When the thermostat is satisfied, contacts open, deenergizing C.
The COMP and OFM stop, and the IFM stops after the preselected
time delay.
On the loss of the thermostat call for cooling, 24 V is removed
from both the "Y1/Y" and "G" terminals (provided the fan switch
is in the "AUTO" position) de- -energizing the compressor
contactor and opening the contacts supplying power to
compressor/OFM. After a 90- -second delay, the IFM shuts off. If
the thermostat fan selector switch is in the "ON" position, the IFM
will run continuously.
Heating — On a call for heat, thermostat makes circuites "R" to
"Y) and "R" to "G".
A circuit is made to C, starting COMP and OFM. Circuit "R" to
"G" also is complted, energizing IFR and starting IFM after the
selected time delay.
Should room temperature continue to fall, circuit "R" to "W" is
made through second- -stage thermostat. 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.
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 third 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.
NOTE:
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.
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