Fig. 10 -- defrost control – Bryant Preferredt Series with Puronr Refrigerant 223A User Manual

Page 6

Sequence of Operation
NOTE: Defrost control board is equipped with 5 minute lockout
timer that is initiated upon any interruption of power.
Turn on power to indoor and outdoor units. Transformer is
energized.
Cooling
On a call for cooling, thermostat makes circuits R--O, R--Y, and

R--G. Circuit R--O energizes reversing valve, switching it to
cooling position. Circuit R--Y sends low voltage through the

safeties and energizes the T1 terminal on the circuit board. If the

compressor has been off for 5 minutes, or power has not been
cycled for 5 minutes, the OF2 relay and T2 terminal will energize.

This will close the contactor, and start the outdoor fan motor and
compressor.
When the cycle is complete, R--Y is turned off, stopping the

compressor and outdoor fan. The 5 minute time guard begins
counting. Compressor will not come on again until this delay

expires. In the event of a power interruption, the time guard will
not allow another cycle for 5 minutes.
NOTE: If the indoor blower off delay is enabled, it will run up to
an additional 90 seconds to increase system efficiency.
Heating
On a call for heating, thermostat makes circuits R--Y and R--G.

Circuit R--Y sends low voltage through the safeties and energizes
the T1 terminal on the circuit board. T1 energizes the defrost logic

circuit. If the compressor has been off for 5 minutes, or power

has not been cycled for 5 minutes, the OF2 relay and T2 terminal
will energize. This will close the contactor, start the outdoor fan

motor and compressor.
When the cycle is complete, R--Y is turned off , stopping the

compressor and outdoor fan. The 5 minute time guard begins
counting. Compressor will not come on again until this time delay

expires. In the event of a power interruption, the time guard will

not allow another cycle for 5 minutes.
Quiet Shift
Quiet shift is a field selectable defrost mode (factory set to OFF),
which will eliminate occasional noise that could be heard at the

start of defrost cycle and restarting of heating cycle. It is selected

by placing DIP switch 3 on defrost board (see Fig. 10) in the ON
position.
When Quiet Shift switch is placed in ON position, and a defrost is
initiated, the following sequence of operation will occur. Reversing

valve will energize, compressor will turn off for 30 seconds, and

then turn back on to complete defrost. At the start of heating after
conclusion of defrost, reversing valve will de--energize,

compressor will turn off for another 30 seconds, and the fan will
turn off for 40 seconds, before starting in the heating mode.

Defrost
The defrost control is a time/temperature control which has field

selectable settings of 30, 60, 90, or 120 minutes, factory set to 90
minutes. These settings represent the amount of time that must pass

after closure of the defrost thermostat before the defrost sequence

begins.
The defrost thermostat senses coil temperature throughout the

heating cycle. When the coil temperature reaches the defrost
thermostat setting of approximately 32_F (0 _C), it will close,

which energizes the DFT terminal and begins the defrost timing

sequence. When the DFT has been energized for the selected time,
the defrost cycle begins. Defrost cycle is terminated when defrost

thermostat opens, or automatically after 10 minutes.
Defrost Speedup
To initiate a forced defrost, speedup pins (J1) must be shorted with

a flat head screwdriver for 5 seconds and RELEASED. If the
defrost thermostat is open, a short defrost cycle will be observed

(actual length depends on Quiet Shift switch position). When Quiet
Shift is off, only a short 30 second defrost cycle is observed. With

Quiet Shift ON, the speedup sequence is one minute; 30 second
compressor off period followed by 30 seconds of defrost with

compressor operation. When returning to heating mode, the

compressor will turn off for an additional 30 seconds and the fan
for 40 seconds.
If the defrost thermostat is closed, a complete defrost cycle is
initiated. If the Quiet Shift switch is turned on, the compressor will

be turned off for two 30 second intervals as explained previously.

OF2

HK32EA003

QUIET

SHIFT

120

INTER

L
TIMER

OFF

DFT

O R

Y C

T2 C C O

DFT

SPEEDUP

Speedup
Pins

Defrost interval
DIP switches

Quiet
Shift

A05378

Fig. 10 -- Defrost Control

223A

/225B