186CNV / 284ANV: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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Code 25-24 Model Plug Changed
Code 25-24 indicates that the model plug presently installed is different
from the previously stored valid model plug value. Code 25-24 will be
set when the equipment is powered up with a valid model plug value that
is different from the stored model plug value in memory. A changed
model plug will affect control configuration only if that model plug was
present when power was applied to the equipment. Code 25-24 will be
set if the model plug is changed to a different valid value or an invalid
value while power is applied to the unit. If the model plug change is
intentional, then no corrective action is required. Leave the new model
plug in place and the code will clear on its own when power is removed
and reapplied to the equipment. If the model plug change is not
intentional, then remove power from the equipment, install the correct
model plug, and reapply power to the equipment.
Code 25-61 Invalid Model Plug Lockout
Each system requires a model plug to be installed on the PCM. The
model plug consists of two resistors in a unique combination. This
model plug identifies the system size and type so PCM software can
apply the relevant operating limits and reference correct operating
tables. Code 25-61 designates the currently installed model plug is not
valid and does not match any possible model in variable speed software.
Consult unit installation instructions for model plug to unit model cross
reference and replace model plug with correct part. While Code 25-61 is
active, the unit will not be operable.
Code 25-63 VFD System Lockout - Model Mismatch
This code is generated when the sensed physical model plug is
recognized but not compatible with the installed VFD. Check installed
model plug against table in installation instructions for the model being
serviced. Replace with correct VFD or model plug part.
Code 26-26 PCM MCU Old Version A
This fault is set when the PCM microcontroller on installed board is
recognized as old. This board should not be used in the field and should
be returned to Bryant for warranty replacement.
Code 26-27 PCM Reprogramming Failure
Code 26-27 indicates that an attempt for the PCM to reprogram itself
failed. If this diagnostic is not recent, then a subsequent reprogramming
attempt may have succeeded. The technician should check the current
PCM software version against the latest software release. If the PCM
software is not the most current, then the PCM should be reprogrammed
manually using the Evolution Control or the Bryant Service Tech App.
Code 26-31 External EEPROM Write Failure
The PCM stores equipment configuration information in non-volatile
EEPROM memory. An active Code 26-31 can be corrected only by
replacing the PCM.
Code 28-71 Fuse 1 Open Lockout
This code will be set if fuse 1 is blown or missing on PCM board. Fuse 1
powers PEV, RVS, and Bluetooth module. When fuse 1 is open none of
these components will function. AC units will operate if pressure
differential is below the maximum allowable starting threshold (100psi),
but HP units will not operate at all. The code will clear once short is
removed and fuse is replaced with new, undamaged part. If fuse is blown
there is a likely short in either the PEV, RVS, or Bluetooth module
harnesses. If no physical damage is observed, begin by unplugging all
components from PCM and make connections until replacement fuse
opens. Harness should be repaired before replacing fuse. See wiring
diagram for fuse size and location
Code 28-72 Fuse 2 Open Lockout
This code will be set if fuse 2 is blown or missing on PCM board. Fuse 2
only powers the LLS. When this fault is active the system will not
operate. The code will clear once fuse is replaced with new, undamaged
part. LLS are field installed accessories. Check LLS wiring for shorts.
See wiring diagram for fuse size and location.
Code 31-11 Compressor High Pressure Limiting
Code 31-58 Compressor High Pressure Lockout
This system contains a discharge pressure transducer to ensure
compressor reliability. The high pressure limit is based on compressor
model and varies with operating speed. When this fault occurs, the
system will shut down and restart after 5 minute compressor protection
time delay if demand is still present. Each time the fault occurs the
maximum allowable compressor speed will be reduced by 25% until the
minimum allowable compressor speed is reached. Each hour of
compressor operation without fault re-occurrence will increase the
compressor speed limit by 25%. This ensures that partial operation is
still possible and system will self-correct if the issue causing fault is
removed. Code 31-58 occurs when the compressor high pressure limit is
reached while the compressor is at its minimum operating speed. System
will "lock out" for 2 hours and attempt to resume normal operation
afterwards. Multiple external factors may generate this fault: Dirty
condenser, lack of airflow across condenser, condenser airflow
recirculation, extreme high temperature and sun loading, refrigerant
circuit blockage, faulty EXV/TXV, or overcharge.
Code 31-16 High Pressure Switch Shutdown
This system contains a 670psi high pressure switch as well as a
discharge pressure transducer. This fault should not occur as the pressure
transducer utilizes a separate high pressure limit at a lower setting. In the
case of a fast transient this switch will safely disable system operation.
This switch is connected directly to VFD and a break or short in wire
harness during high pressure events will also generate fault. The high
pressure switch quickly shuts down high voltage to VFD and additional
communication faults may occur since the VFD will cease to
communicate with PCM. The PCM/VFD will not attempt to resume
system operation until discharge pressure has dropped below 425PSIG.
Ensure HPS is closed and securely connected to VFD.
Code 31-19 High Pressure Disable
This fault is triggered when the discharge pressure is too high to start
compressor (620psig). If refrigerant saturated pressure is high enough
the system will be inoperable until pressures drop to acceptable range.
Extreme high ambient temperatures may cause this fault to set and
system will be inoperable during this time.
Code 32-15 Compressor Low Suction Shutdown
Code 32-55 Compressor Low Suction Lockout
Exceeding soft and hard low pressure limits result in code 32-15. The
soft low pressure limit can be exceeded for up to 2 minutes before code
is generated, while exceeding the hard limit immediately results in code
32-15. Low pressure limits are compressor and rpm dependent, but 30psi
and 15psi are typical. 4 occurrences of code 32-15 result in a 2hour
lockout. Note: AEM will attempt to mitigate low pressure by adjusting
system operation. This fault will only be set if system operation cannot
be modified quickly enough to prevent exceeding hard and soft limits. A
single occurrence of fault will result in 5 minute time delay followed by
attempted restart if demand is still present.
Low pressure conditions can occur from multiple causes: Blockage in
liquid line, stuck TXV or EXV, no airflow across evaporator, low system
charge. Low ambient temperatures will increase diagnostic sensitivity to
contributing factors above. Check pressure drop of liquid line at
condenser and evaporator, confirm airflow across evaporator, and
confirm system charge is correct. Replace EXV/TXV if necessary.
