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U U n n i i t t S S t t a a r r t t u u p p
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.)
D D e e f f r r o o s s t t C C o o n n t t r r o o l l C C h h e e c c k k o o u u t t
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, proceed to
the Demand Defrost Control Checkout table.
T T e e s s t t S S e e n n s s o o r r s s
Using the chart below, locate (as close as possible) the
actual sensor temperature. The measured resistance
should be relatively close to the resistance value
shown in the chart.
Example:
Table 12. Demand Defrost Control Checkout Table
SYMPTOMS
1.
LED off.
2.
LED flashing very rapidly
(greater than 4 times/ sec) or
appears to be on continuously.
22
CHECKS
1.
24V R-B & Y-B at board, with unit
running?
2.
Short FRC_DFT pin to TEST_COMMON
pin. Is defrost cycle initiated?
TEST_COMMON pin shorted to TST pin?
Sensor temp. = 19°F.
Measured Resistance = 46K ohms
This sensor is good since the measured value is
relatively close to the chart value.
1 — Flash/
= Normal operation.
Second
= Fault A (Low ΔT): Inoperative compressor,
2 — Flashes/
loss of charge, open ambient sensor, shorted
Second
coil sensor.
= Fault B (20 defrosts terminated on time)
Fault C (High ΔT): SOV stuck in heating,
3 — Flashes/
shorted ambient sensor, open coil sensor,
Second
closed TXV, OD motor failure, OD fan on in
defrost, undercharged unit.
4 — Flashes/
= Fault A & C or A & B
Second
For additional information consult Pub. No. 34–1001 Heat Pump
Defrost Controls.
TEMP (ºF)
86
81
75
70
65
59
55
50
45
41
36
32
25
19
14
10
5
0
YES/NO
ACTIONS
Repair low voltage wiring.
N
Complete Check #2.
Y
Replace defrost control.
N
Y
LED is bad but control will still function.
Y
Remove short.
Replace defrost control.
N
RESISTANCE
7.85K
8.85K
10.24K
11.59K
13.14K
15.32K
16.93K
19.41K
22.20K
24.76K
28.45K
31.84K
37.50K
46.44K
53.94K
57.64K
67.06K
78.05K
18-BB35D1-16B-EN
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