5604542-UIM-B-0419
Johnson Controls Ducted Systems
13
SECTION IX: 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 shorting the TEST terminals for
three seconds while the thermostat is calling for compressor operation
(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 Figure 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 sec-
tions of this document.
TABLE 11:
TEST Input Functionality with Y
Duration of connection (seconds)
Control behavior with thermostat signals present
< 2
No response
2-5
Bypass ASCD (Reduce timer to zero immediately). If Y1 is present and high-pressure switch is closed,
contactors will be energized.
Clear Pressure Switch Lockout and reset the 6 hour PS timer.
> 5
Initiate defrost cycle ignoring the COIL temp and record that defrost cycle was initiated by TEST short.
Energize Wout
and begin defrost cycle immediately upon expiration of timer.
Test Pin Short removed
Terminate defrost as normal.
Test pin Short not removed
Continue defrost cycle until TEST connection removed.
TABLE 12:
TEST Input Functionality without Y
Duration of connection (seconds)
Control behavior with thermostat signals NOT present
< 2
No response
2-5
The control shall sequentially flash, on the STATUS LED, the series of stored error codes (up to the last 5
since active error codes were last cleared) starting with the most recent. If there are no error codes stored
in memory, the STATUS LED shall flash 3 times (0.1 sec ON / 0.1 sec OFF).
> 5
The control shall immediately clear the stored error code array, reset the 6 hour PS timer and flash the
STATUS LED 6 times (0.1 sec ON / 0.1 sec OFF) to indicate that the error memory has been cleared.
FIGURE 13:
Heat Pump Flow Diagram
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