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18-BC92D1-1G-EN
Defrost Control (Heat Pump only)
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The demand defrost control measures heat pump
outdoor ambient temperature with a sensor located
outside the outdoor coil. A second sensor located on
the outdoor coil is used to measure the coil
temperature. The difference between the ambient and
the colder coil temperature is the difference or delta-T
measurement. This delta-T measurement is
representative of the operating state and relative
capacity of the heat pump system. By measuring the
change in delta-T, we can determine the need for
defrost. The coil sensor also serves to sense outdoor
coil temperature for termination of the defrost cycle.
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A fault condition is indicated by the CDA connected to
the control board inside the heat pump control box.
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Demand Defrost is enabled with the following inputs to
the Integrated Variable Speed Control (IVSC):
•
Outdoor ambient temperature sensor (ODS-B)
reporting an outdoor temperature at or below 52° F.
•
Coil temperature sensor (CBS) reporting a coil
temperature at or below 35° F.
•
Heat/Cool Demand (HCD) from the communicating
comfort control for at least two minutes or more.
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The calculated temperature difference between the
outdoor temperature sensor and the coil temperature
sensor is called Delta T. Defrost can occur once the
current Delta T exceeds the Delta T initiate value. The
Defrost initiate value is calculated using a clean-coil
Delta T x 2.0, plus a temperature bin correction factor.
Initiation Delta T will automatically adjust based on the
outdoor temperature. This adaptive logic assures a
complete defrost for a range of outdoor temperatures.
65ºF
60ºF
55ºF
50ºF
45ºF
40ºF
35ºF
30ºF
-40ºF
-20ºF
0ºF
20ºF
40ºF
60ºF
FACTORY TERMINATION TEMP
AMBIENT TEMPERATURE
TERMIN
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TEMPE
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MEDIUM TERMINATION TEMP
HIGH TERMINATION TEMP
DEFROST TERMINATION PROFILES
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Figure 6.
CDA Mini Menu
FRC DFT
PRESS ENTER
TEST IN PROGRESS
CTS <value>
TEST COMPLETE
CONTROL MENU
CONFIG
MENU
MONITOR
MENU
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1. System must be running with demand from the
thermostat.
2. FRC DFT TEST can be initiated in heat mode only.
3. Press ENTER to begin forced defrost.
4. Execute Forced Defrost following Forced Defrost
(Defrost terminates on Coil Temperature or
maximum time override of 15 minutes).
5. When test begins, TEST IN PROGRESS displays on
line 1 and Coil Temperature value on line 2.
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e:: Home Screen, under System Status will display
DEFROST.
6. When test is complete, TEST COMPLETE displays
for 10 seconds.
7. If there is a defrost fault condition, test terminates
and sends alert to the alert menu.
8. For more information, refer to the Alert Code Tables
in Service Facts and Technical Service Manual (Pub.
No. 34–4301–01) documents.
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e:: Screens will update as the test proceeds.
