Reversing Valve Control; Compressor Control; Auxiliary (Electric) Heat Control; Defrost - Bryant Preferred 549K 04-06 Service And Maintenance Instructions

POINT NAME
INPUTS
G Fan
Y1 Cool 1
Y2 Cool 2
W1 Heat 1
W2 Heat 2
R Power
C Common
DFT 1
DFT 2
OUTPUTS
IFO Fan On
OF OD Fan On
RVS1
RVS2
COMP 1
COMP2
HEAT 2
COM
CONFIGURATION
Select Jumper
SPEED-UP CONFIGURATION
Speed-Up Jumper
Speed-Up Jumper
NOTES:
1. Jumper for 1-3 seconds: Factory Test — The defrost interval timing is reduced by a factor of 0.1 seconds/minute based on the positions of DIP
switches SW1 and SW2 (i.e., 90 minutes will be reduced to 9 seconds).
2. Jumper for 5-20 seconds: Forced Defrost — Defrost runs for 30 seconds if DFT2 is open.

Reversing Valve Control

The DFB has two outputs for unit reversing valve control. Op-
eration of the reversing valves is based on internal logic; this
application does not use an "O" or "B" signal to determine re-
versing valve position. Reversing valves are energized during
the cooling stages and the defrost cycle and de-energized
during heating cycles. Once energized at the start of a cooling
stage, the reversing valve will remain energized until the next
heating cycle demand is received. Once de-energized at the
start of a Heating cycle, the reversing valves will remain de-en-
ergized until the next cooling stage is initiated.

Compressor Control

The DFB receives inputs indicating Stage 1 Cooling, Stage 2
Cooling and Stage 1 Heating from the space thermostat or unit
control system (RTU Open controller); it generates commands
to start compressors with or without reversing valve operation
to produce Stage 1 Cooling (one compressor runs), Stage 2
Cooling (both compressors run) or Stage 1 Heating (both com-
pressors run).

Auxiliary (Electric) Heat control

The 549K unit can be equipped with one or two auxiliary elec-
tric heaters, to provide a second stage of heating. The DFB will
energize this Heating System for a Stage 2 Heating Command
(heaters operate concurrently with compressor(s) in the Stage 1
Heating cycle), for an Emergency Heating sequence (compres-
sors are off and only the electric heaters are energized) and also
during the Defrost cycle (to eliminate a "cold blow" condition
in the space).
Table 7 — 549K Defrost Board I/O and Jumper Configurations
TYPE OF I/O CONNECTION PIN NUMBER
DI, 24 vac
DI, 24 vac
DI, 24 vac
DI, 24 vac
DI, 24 vac
24 vac
24 vac
DI, 24 vac DFT-1 to DFT-1
DI, 24 vac DFT-2 to DFT-2
DO, 24 vac
DO, 24 vac
DO, 24 vac
DO, 24 vac
DO, 24 vac
DO, 24 vac
DO, 24 vac
24 vac
24 vac
—
—
UNIT CONNECTION
P2-3
P2-5
P2-4
P2-7
P2-6
P3-1 CONTL BRD-8
P3-2 CONTL BRD-4
P3-9 REHEAT/HP-2
OF
P3-7 to P3-5
P3-6 to P3-4
P3-10 FPT1-REHEAT/HP-6
P3-8 FPT2-REHEAT/HP-8
E-HEAT
P3-3
P1-1
JMP17
JMP18

Defrost

The defrost control mode is a time/temperature sequence.
There are two time components: The continuous run period
and the test/defrost cycle period. The temperature component
is provided by Defrost Thermostat 1 and 2 (DFT1 and DFT2)
mounted on the outdoor coil.
The continuous run period is a fixed time period between the
end of the last defrost cycle (or start of the current Heating cy-
cle) during which no defrost will be permitted. This period can
be set at 30, 60, 90 or 120 minutes by changing the positions of
DIP switches SW1 and SW2 (see Fig. 31 and Table 8). The de-
fault run period is 30 minutes.
Shorting the jumpers for a period of 5 to 20 seconds bypasses
the remaining continuous run period and places the unit in a
Forced Defrost mode. If the controlling DFT is closed when
this mode is initiated, the unit will complete a normal defrost
period that will terminate when the controlling DFT opens or
the 10 minute defrost cycle limit is reached. If the controlling
DFT is open when this mode is initiated, the Defrost cycle will
run for 30 seconds. Both modes end at the end of the Defrost
cycle.
Fig. 31 — DIP Switch Settings - Defrost Board
19
NOTE
CTB-G
CTB-Y1
CTB-Y2
CTB-W1
CTB-W2
—
—
OFR
— Energize in COOL
— Energize in COOL
TB4-1
TB4-3
—
—
—