035-20401-001 Rev. A (0904)
8
Unitary Products Group
SECTION VIII: SYSTEM OPERATION
REQUIRED CONTROL SETUP
IMPORTANT: The following steps must be taken at the time of
installation to insure proper system operation.
1.
Consult system wiring diagram to determine proper thermostat
wiring for your system.
2.
If hot heat pump configuration is desired, change HOT HEAT
PUMP jumper to ON position.
3.
If installation includes a fossil fuel furnace, change FFUEL jumper
to ON position.
4.
Set low temperature cutout (LTCO), balance point (BP), switch
point (SP), and Y2 Lock jumpers as desired.
5.
Verify proper system functionality. Confirm room thermostat opera-
tion including fault code display capability.
6.
Upon completion of installation, verify that no fault codes are
stored in memory. Clear the fault code memory if necessary.
ANTI-SHORT CYCLE DELAY
The control includes a five-minute anti-short cycle delay (ASCD) timer
to prevent the compressor from short cycling after a power or thermo-
stat signal interruption. The ASCD timer is applied when the control is
first powered from the indoor unit thermostat and immediately following
the completion of a compressor run cycle. The compressor and the out-
door fan will not operate during the five minutes that the timer is active.
The ASCD timer can be bypassed by connecting the TEST terminals
for three seconds while the thermostat is calling for compressor opera-
tion (Y1 input signal energized).
LOW VOLTAGE DETECTION
The control monitors the transformer secondary (24 VAC) voltage and
provides low voltage protection for the heat pump and its components.
In particular, the control prevents contactor chatter during low voltage
conditions. If the voltage drops below approximately 19 VAC, the con-
trol will continue to energize any relays that are already energized but
will not energize any additional relays until the voltage level increases.
If the voltage drops below approximately 16 VAC, the control will imme-
diately de-energize the relay outputs and will not energize any relays
until the voltage level increases. The control will store and display the
appropriate fault codes when low voltage conditions occur.
CRANKCASE HEATER
The control energizes the crankcase heater terminal (CCH) whenever
line voltage is applied to the control and the outdoor fan is not on. If the
compressor is equipped with a crankcase heater, it will be energized
from the CCH terminal of the control.
TEST INPUT
The control includes a TEST input connector that can be used for vari-
ous testing functions during installation and service. The TEST input
connector is shown in Figures 11 & 14. The following table summarizes
the behavior of the control when the two TEST pins are connected.
More detailed descriptions of the various functions are included in other
sections of this document.
FIGURE 11:
Demand Defrost Control Module
TABLE 1:
TEST Input Functionality
Duration of
connection (seconds)
Control behavior with no
thermostat signals present
Control behavior with thermostat signals present
Less than 2
No response
No response
2-6
Display operational mode
Bypass ASCD. If Y1 is present and high-pressure switch is
closed, contactors will be energized.
Clear soft lockout
Clear soft lockout
Clear hard lockout
Clear hard lockout
More than 6
Display operational mode
Energize X/L with active defrost curve flash code
Initiate defrost cycle ignoring the liquid line and outdoor ambient temp.
Energize X/L with active defrost curve flash code
Connection removed
Resume normal LED display
Terminate defrost as normal or until O signal is energized.
Connection not removed
Display operational mode
Energize X/L with active defrost curve flash code
Continue defrost cycle and X/L flash code until
TEST connection removed.
