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FIGURE 13: Demand Defrost Control Module
FAULT CODE DISPLAY
The control shall provide status codes using the LED. Status codes
indicate the state of operation of the unit but do not represent a fault.
The table below describes the LED displays during status codes. Status
codes will not be displayed when a fault code is present.
TABLE 5: Status Code Display
No Faults active
No power to the control
Nothing energized
Compressor Operation
No Faults active
Active
M energized
Control normal operation –
No faults active
no call for compressor
Y not present
No faults active,
Control normal operation –
Y present, ASCD
in ASCD period
timer not expired
The control shall provide fault codes using the Status LED. The table
below describes the LED displays during fault codes. Unless otherwise
specified, the control shall provide flashes that are a 1/3 second on and
1/3 second off for fault codes. The control shall only display a single
fault code on the LED. The control shall display the fault code on the
LED repeatedly with a 2 second off period between repetitions of the
fault code. If multiple fault codes are present at the same time, the LED
shall display only the most recent fault.
The table below shows a number that represents the number of flashes
for the specified code. For instance, a flash code entry of 3 indicates
that the control will energize the output for three 1/3 second on, 1/3 sec-
ond off flashes, wait two seconds, then energize the output for three
more 1/3 second on, 1/3 second off flashes and repeat.
Johnson Controls Unitary Products
TABLE 6: Status
OFF
ON
2s ON/2s OFF
0.1 sec ON/0.1 sec OFF
Demand Defrost
The control maintains proper airflow through the outdoor coil during
heating operation by melting frost and ice that may form on the coil.
Frost may accumulate unevenly in different sections of the coil because
of the arrangement of the refrigeration circuit within the coil. The control
may initiate a defrost cycle even when the coil is not completely cov-
ered with frost. This is normal operation.
The control regulates the defrost operation of the heat pump based on
accumulated compressor run time, outdoor coil temperature, and out-
door ambient temperature. The control will cause the heat pump unit to
operate in the normal heating mode until it determines that a defrost
cycle is needed.
All defrost timings are based on accumulated compressor run time.
Description
High -pressure switch fault (not in lockout yet)
System in high-pressure switch lockout
(last mode of operation was normal compressor
operation)
System in high-pressure switch lockout
(last mode of operation was defrost)
System in low-pressure switch lockout
(last mode of operation was normal compressor
operation)
Low Voltage (<19.2VAC) preventing further
relay outputs for > 2 seconds
Low Voltage (<16VAC) stopped current relay
outputs for > 2 seconds
Coil sensor failure (Open or Shorted)
Outdoor ambient sensor failure (Open or Shorted)
Control Failure
5121495-UIM-D-0516
STATUS LED
2 Flashes
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
9 Flashes
10 Flashes
11
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