18-BC85D1-2 17
11.3 Defrost Control
Defrost controls have a selectable termination temperature. As shipped, defrost will terminate at 47°F. For a
higher termination temperature, cut Jumper J2 to achieve 70°F when at or below 30°F ambient. See Service
Facts shipped in the outdoor unit for more information.
Pin Identification (See Illustration at right)
1. TEST_COMMON (Shorting any of the other pins to this pin causes the function of the other pin to be
executed. Leaving this pin open results in the normal mode of operation.)
2. TST = Test (Shorting TEST_COMMON to this pin speeds up all defrost board timings.)
3. FRC_DFT = Forced Defrost (Short TEST_COMMON to this pin for two (2) seconds to initiate a forced
defrost. Remove the short after defrost initiates.)
Defrost Control Checkout
Normal operation requires:
• LED on board flashing 1 time/second.
• 24V AC between R & B.
• 24V AC between Y & B with unit operating.
• Defrost initiation when FRC_DFT pin is shorted to TEST_COMMON pin.
If a defrost control problem is suspected, refer to the service information in control box.
Defrost Termination Temperatures
Outdoor
Temperature
Termination
Temperature
As
Shipped
>22°F 47°F
10°F–22°F ODT + 25°F
6°F–10°F 35°F
Cut
Jumper 2
>30°F 47°F
6°F–30°F 70°F
All < 6°F
12 min. or 35°F
every 3 hrs.
Defrost Board
Detail
J1
U1
J2
J3
FRC_DFT
TST
TEST_COMMON
JUMPER 2
TEST PINS
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