18-BC117D1-1B-EN 21
1. Initiate Adaptive/Timed Limp Mode so long as Coil
Temp Sensor is functional. Monitor actual time
in defrost and add or reduce run time until next
forced defrost based on achieving a 4 minute (+/-
1) defrost period.
2. This defrost control utilizes a safety strategy
called “Adaptive Limp Mode”. Adaptive limp mode
is dened as a timed heating mode following rapid
defrosts (accumulated heating times between de-
frost totaling less than 15 minutes). Once invoked
the DFC will limit defrost periods and maximize
heating capacity. While in adaptive limp mode
the DFC will monitor heating and defrost periods
for no longer than 10 cycles. The DFC will then
release the board to demand defrost; however, if
the LPCO trips while in limp mode the system will
initiate a soft lockout and exit limp mode.
If both Coil Temp Sensor and Ambient Temp Sen-
sor have failed, initiate a 5 minute forced defrost
every 60 minutes of run time. This in conjunction
with the normal low pressure trip, will initiate a soft
lockout.
a. A short heating cycle that enters defrost in 15
minutes or less and/or enters two more defrosts
with less than 15 minutes of accumulative
run time each will enter an Adaptive Limp
Mode (6 Flash).
b. Coil sensor failure will initiate a Timed Limp
M o d e . T h i s w i l l b e a c c o m p a n i e d b y a 2 a s h .
The DFC will initiate defrost after 60 minutes of
accumulated heating runtime and terminate
after a 5 minute defrost. The limp mode will
clear after the sensor fault is cleared.
c. Ambient sensor failure will initiate an Adaptive
Timed Limp Mode. This will be accompanied
b y a 1 a s h . T h e D F C w i l l i n i t i a t e d e f r o s t a f t e r
60 minutes of accumulated heating runtime
and force a defrost, which will terminate on
coil temp. The limp mode will clear after the
sensor fault is cleared.
d. This could be caused by a condenser fan motor
failure, low charge or other reasons.
3. The rst 15 minute soft lockout the system will
return to normal operation. Should this continue
to operate in this manner there will be a 30 minute
soft lockout and so on. At the end of the lockout
process, if a hard lock is necessary, a 4 ash
will be announced and system operation is inter-
rupted. If the ambient temperature climbs above
40°F for more than 30 minutes this clears this fault
count and resumes normal operation.
a. If or when normal operation is restored after
the ambient temperature climbs above 40°F
for more than 30 minutes and another LP
trip is monitored on the 9th trip this will initiate
a hard lockout that will not be cleared by
temperature or time.
4. Once ambient drops to -12 or lower wait 5 minutes
before soft lockout begins. During soft lockout the
Y signal passes through to the X2 output. Resume
operation when ambient temperature rises to -3°F
or higher and after 5 minute soft lockout period
expires. LPCO should reset around 5°F.
5. During a Hard Lockout, the X2 relay opens so that
the Y signal does not pass through.
LED
FAULT
CODES
FAULT
DESCRIPTION
DEFROST
CONTROL
BEHAVIOR
4 FLASH
Hard Lock Out (can
only be cleared
with a low voltage
power cycle)
Occurs after 9
th
trip
of LPCO. See Note 6.
5 FLASH Soft Lock Out
5 flash goes away
after soft lockout
period expires. See
Note 2.
6 FLASH
Defrost cycles too
close together
Heating short cycle
fault triggers 6 flash.
The system will follow
10 adaptive time
heating cycles and
then return to
demand defrost.
9 FLASH
Low Ambient Soft
Lockout. Out-
door temperature
dropped below 3°F.
(OFF at -12°F/ON
at 3°F)
Outdoor temperature
is below -12°F. See
Note 5.
LPCO HEATING Mode Flash Code
1
st
Trip
15 minute soft lock-
out period
5 and 6 flash
2
nd
Trip
30 minute soft lock-
out period
5 and 6 flash
3
rd
Trip
45 minutes soft lock-
out period
5 and 6 flash
4
th
– 8
th
Trip
18 hour soft lock-out
period
5 and 6 flash
9
th
Trip
(a)
Hard lock-out 4 flash
LPCO HEATING Mode Flash Code
1
st
Trip
15 minute soft lock-
out period
5 and 6 flash
2
nd
Trip
30 minute soft lock-
out period
5 and 6 flash
3
rd
Trip
45 minutes soft lock-
out period
5 and 6 flash
4
th
– 8
th
Trip
18 hour soft lock-out
period
5 and 6 flash
9
th
Trip
(a)
Hard lock-out 4 flash
(a)
If LPCO is open, a 3 flash can accommodate any of the
faults above and will clear when the LPCO closes.
Note: Once the LPCO closes, the 3 flash fault will not cont-
inue showing – only 5 flash if in the softlockout period.
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