20
Specifications subject to change without notice.
516 01 3604 04
Fig. 34 — Typical Low-Voltage Control Connections
CENTRAL TERMINAL BOARD
The Central Terminal Board (CTB) is a pass through con
-
nection point. The CTB provides the capability to add facto
-
ry-installed options and field-installed accessories to the
units by cutting jumper wires without having to change or re
-
route wires through the structure of the unit. The CTB does
not provide any microprocessor control; it is simply a basic
multifunction wiring terminal configuration.
COMMERCIAL DEFROST CONTROL
The Commercial Defrost Control Board (DFB) coordinates
thermostat demands for supply fan control, 1 or 2 stage
cooling, 2 stage heating, emergency heating and defrost
control with unit operating sequences. The DFB also pro
-
vides an indoor fan off delay feature (user selectable). See
Fig. 35 for board arrangement.
The DFB is located in the RHH unit’s main control box (see
Fig. 2 and 36). All connections are factory-made through
harnesses to the unit’s CTB, to IFC (belt-drive motor) or to
ECM (direct-drive motor), reversing valve solenoids and to
defrost thermostats. Refer to Table 6 for details of DFB In
-
puts and Outputs.
Fig. 35 — Defrost Control Board Arrangement
Reversing valve control
The DFB has two outputs for unit reversing valve control.
Operation of the reversing valves is based on internal logic;
this application does not use an “O” or “B” signal to deter
-
mine reversing valve position. Reversing valves are ener
-
gized 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 ener
-
gized until the next heating cycle demand is received. Once
de-energized at the start of a Heating cycle, the reversing
valves will remain de-energized 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 ther
-
mostat or unit control system; 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
compressors run).
Auxiliary (Electric) Heat control
The RHH unit can be equipped with one or two auxiliary
electric 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 compres
-
sor(s) in the Stage 1 Heating cycle), for an Emergency
Heating sequence (compressors are off and only the elec
-
tric heaters are energized) and also during the Defrost cycle
(to eliminate a “cold blow” condition in the space).
X
C
G
W2
R
C
W2
G
W1
O/B/Y2
Y2
W1
R
Y1
Y1
Typical
Thermostat
Connections
T
H
E
R
M
O
S
T
A
T
(Note 1)
(Note 2)
1. Typical multi-function marking. Follow manufacturer’s configuration
instructions to select Y2. Do not configure for O output.
2. W2 connection not required on units without electric heating.
Field Wiring
Central
Terminal
Board
NOTES:
DIP
SWITCHES
SPEED-UP
JUMPERS
