335224-BIM-B-1208
Johnson Controls Unitary Products
51
COMPRESSOR PROTECTION
In addition to the external pressure switches, the compres-
sors also have inherent (internal) protection. If there is an
abnormal temperature rise in a compressor, the protector will
open to shut down the compressor. The UCB incorporates
features to minimize compressor wear and damage. An
Anti-
Short Cycle Delay (ASCD)
is utilized to prevent operation of
a compressor too soon after its previous run. Additionally, a
minimum run time is imposed any time a compressor is ener-
gized.
The ASCD is initiated on unit start-up and on any compressor
reset or lock-out.
FLASH CODES
The UCB will initiate a flash code associated with errors
within the system. Refer to UNIT CONTROL BOARD FLASH
CODES Table 41.
RESET
Remove the call for cooling, by raising thermostat setting
higher than the conditioned space temperature. This resets
any pressure or freezestat flash codes.
REHEAT MODE SEQUENCE OF OPERATION
The reheat control board allows the user to select two differ-
ent modes of operation via a jumper connection on the board.
(See Figure 3.) Each mode is described below. Refer to Fig-
ures 3 - 5 when reading this section.
“NORMAL” MODE
When the reheat control board (RCB) detects a need for
dehumidification (24VAC) at "HUM" via the field supplied
dehumidistat connected to RHTB-1 and RHTB-2 and there is
not a call for cooling, it energizes the hot gas relay (HGR),
which energizes the 3-way valve (SOL 3), the condenser coil
valve (SOL 2), and de-energizes the reheat coil bleed valve
(SOL 1). (In the DK-12, SOL 2 is only energized when the
discharge pressure in circuit #1 rises above 235 psig and de-
energizes SOL 2 after the discharge pressure falls below 175
psig. Both outdoor fans of circuit #1 in the DK-12 also disen-
gage to conserve energy.) The Y1 signal is passed to the unit
control board (UCB), which engages circuit # 1, resulting in
circuit #1 reheat mode operation.
When the room thermostat calls for first stage cooling, with or
without a call for dehumidification, the RCB senses a signal
through "Y1", de-energizing the HGR, which de-energizes
SOL 3 and SOL 2 and energizes SOL 1, engaging circuit #1,
resulting in circuit #1 cooling mode operation.
When the room thermostat calls for second stage cooling, the
RCB senses a signal through "Y1" & "Y2" and engages circuit
#1 and circuit #2 in cooling mode.
Indoor blower operation is initiated upon a call for first stage
cooling, second stage cooling or dehumidification.
Anytime there is a call for 2 stages of cooling, the unit will not
operate in the reheat mode, even if there is a call for dehu-
midification at "HUM".
The unit will not operate in the reheat mode if there is any call
for heating.
On units with economizers, the unit will not operate in the
reheat mode if there is a call for cooling and the economizer
is operating as first stage of cooling.
All safety devices function as previously described.
"ALTERNATE” MODE
When the RCB detects a need for dehumidification (24VAC)
at "HUM" via the field supplied dehumidistat connected to
RHTB-1 and RHTB-2, and there is not a call for cooling, it
energizes the HGR, which energizes the SOL 3, SOL 2, and
de-energizes SOL 1. (In the DK-12, SOL 2 is only energized
when the discharge pressure in circuit #1 rises above 235
psig and de-energizes SOL 2 after the discharge pressure
falls below 175 psig. Both outdoor fans of circuit #1 in the DK-
12 also disengage to conserve energy.) The unit then oper-
ates with circuit #1 in reheat mode and circuit #2 in cooling
mode.
When the room thermostat calls for first stage cooling while
there is still a call for dehumidification, no operational change
is made. The call for cooling is ignored and the unit continues
to operate with circuit #1 in reheat mode and circuit #2 in
cooling mode.
When the room thermostat calls for second stage cooling, the
RCB senses a signal through "Y1" and "Y2" and de-ener-
gizes the HGR, which de-energizes SOL 3 and SOL 2, and
energizes SOL 1. Both circuits operate in the cooling mode.
Indoor blower operation is initiated upon a call for first stage
cooling, second stage cooling or dehumidification.
Anytime there is a call for 2 stages of cooling, the unit will not
operate in the reheat mode, even if there is still a call for
dehumidification at "HUM".
The unit will not operate in the reheat mode if there is any call
for heating.
All safety devices function as previously described.
