22
18-BB34D1-19B-EN
1 — Flash/
Second
= Normal operation.
2 — Flashes/
Second
= Fault A (Low ΔT): Inoperative compressor,
loss of charge, open ambient sensor, shorted
coil sensor.
3 — Flashes/
Second
= Fault B (20 defrosts terminated on time)
Fault C (High ΔT): SOV stuck in heating,
shorted ambient sensor, open coil sensor,
closed TXV, OD motor failure, OD fan on in
defrost, undercharged unit.
4 — Flashes/
Second
= Fault A & C or A & B
For additional information consult Pub. No. 34–1001 Heat Pump
Defrost Controls.
TEMP (ºF)
RESISTANCE
86 7.85K
81 8.85K
75 10.24K
TEMP (ºF)
RESISTANCE
70 11.59K
65 13.14K
59 15.32K
55 16.93K
50 19.41K
45 22.20K
41 24.76K
36 28.45K
32 31.84K
25 37.50K
19 46.44K
14 53.94K
10 57.64K
5 67.06K
0 78.05K
Table 12. Demand Defrost Control Checkout Table
SYMPTOMS CHECKS
YES/NO
ACTIONS
1. LED off.
1.
24V R-B & Y-B at board, with unit
running?
N
Repair low voltage wiring.
Y
Complete Check #2.
2.
Short FRC_DFT pin to TEST_COMMON
pin. Is defrost cycle initiated?
N
Replace defrost control.
Y LED is bad but control will still function.
2.
LED flashing very rapidly
(greater than 4 times/ sec) or
appears to be on continuously.
TEST_COMMON pin shorted to TST pin?
Y Remove short.
N
Replace defrost control.
3.
Control does not initiate a
normal defrost.
1.
OD Temp. below 49°F.? OD Coil temp.
below 35°F.? "Delta" T increasing
N
Check refrigerant circuits for balanced
distribution of refrigerant if OD coil is
frosting and delta T is not increasing.
2.
LED flashing?
N Refer to SYMPTOM #1.
Y
Complete Check #2.
3.
Check for 24V Y-B at board with unit
running.
N
Repair low voltage wiring.
Y
Complete Check #3.
4.
Check sensors for correct mounting
(connection) and resistance.
Remount or replace sensor if necessary.
5.
Short FRC_DFT pin to TEST_COMMON
pin. Is defrost cycle initiated?
N
Replace defrost control.
Y
Y-B signal or control may be intermittent.
4.
Control does not initiate a
forced defrost.
24V R-B & Y-B at board with unit running?
N
Repair low voltage wiring.
Y
Replace defrost control.
5.
Defrost initiates manually but terminates in less than 10 seconds. Replace defrost control.
6.
Defrost initiates manually but
terminates on time.
1.
Coil sensor circuit open or reading at a
very high resistance?
Y
Replace coil sensor.
2.
Does OD fan cycle off in defrost?
N
Replace defrost control.
3. Windy weather preventing normal
termination?
7.
Defrost initiates on
approximately 15/25 minute
intervals.
1. Be sure OD coil is clean. N
Complete Check #2.
2. Coil sensor open or reading a very high
resistance?
Y
Replace coil sensor.
3.
Ambient sensor reading less than
normal?
N
Complete Check #3.
Y
Replace ambient sensor.
4. OD fan off in defrost? N
Replace defrost control.
UUnniitt SSttaarrttuupp
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