835961-UIM-D-0213
10
Johnson Controls Unitary Products
SECTION V: SYSTEM OPERATION
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 (Y 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.
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 & 12. 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.
FAULT CODE DISPLAY
X/L Output
The X/L terminal of the heat pump control is typically connected to the
X/L input of the room thermostat. The thermostat uses this signal to
notify the homeowner of a problem with the heat pump using an LED or
LCD display. When the control energizes the X/L terminal, the thermo-
stat displays the flash code so the homeowner can see it.
When the control locks out the compressor because of a pressure
switch lockout, it will energize the X/L output as shown in Table 3. The
control has a three second delay between fault code flashes.
If the conditions above exist during cooling mode, the system could be
in the loss of charge condition.
DEFROST OPERATION
Time/Temperature Defrost (13 Seer 2-5 Ton)
The defrost control is a time/temp. control which includes a field-select-
able (tap located at board edge) time period between defrost cycle (30,
60, and 90 minutes). The jumper is factory set at 60 minutes. See Fig-
ure 13.
The electronic timer and the defrost cycle will start only when the con-
tactor is energized and the defrost thermostat is closed. The defrost
thermostat is closed when the liquid temperature falls below approxi-
mately 31° F.
The defrost mode is identical to the cooling mode except that the out-
door fan motor stops and the first stage of heat is turned on through W1
/ 66 to continue warming the conditioned space.
The defrost cycle will be terminated when the defrost thermostat is
opened at 55° F or 10 minutes of compressor accumulated run time,
whichever comes first.
FIGURE 11:
Time/Temp Control Module
FIGURE 12:
Demand Defrost Control Module
90
30
60
Test
RUNTIME
MIN.
SEL
REV
PRESSURE
COMP RLY
DFST
VALVE
OM
XL
XL
R
R
C
C
Y
Y
O
O
W
W
W1/66
W1/66
PRESSURE
SWITCH
DFST
T’STAT
M
M
K2
K1
K3
R3
RUN TIME
30
90
TEST
TEST
RUN TIME
REV
COND.
FA
N
ALTERNATE
CONFIGURATION
ALTERNATE
TEST
AMBIENT
AMBG
COIL
G
COIL
1
2
3
4
COND
FA
N
HIGH
VOL
T
AGE
PRESSURE
M
SWITCH
REV
VALVE
X/L
R
C
Y
O
W
W1/66
X/L
R
C
Y
O
W
W1/66
DEMAND
DEFROST CURVE
SELECTION JUMPER
P
TABLE 2:
TEST Input Functionality
Duration of Connection (seconds)
Control Behavior
Time-Temp
Demand Defrost
Less than 2
Less than 2
No response
2-9
2-6
Bypass ASCD. If Y is present
and pressure switch is closed,
contactors will be energized.
Clear lockout
More than 9
More than 6
Initiate defrost cycle. (Demand
only: Energize X/L with active
defrost curve flash code)
Connection removed
Terminate defrost as normal
Connection not removed
Continue defrost cycle (Demand
only: and X/L flash code) until
TEST connection removed.
TABLE 3:
X/L Output Categories
Condition
X/L
Pressure Switch lockout - last mode of operation was heating 2 flashes
Pressure Switch lockout - last mode of operation was defrost 3 flashes
Incorrect Defrost Curve - jumper selection
On
