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APPENDIX – PROTECTION FUNCTIONS
• Modbus RTU communications with connected devices
(e.g. TZT-100 or SAT-3 thermostat, a Carel Power+
inverter) must continue uninterrupted.
• Modbus RTU communications with a controller such
as a BMS that is controlling the unit must continue
uninterrupted.
Refer to document ‘UC8 Troubleshooting Guide’ for
details.
9 Lock-out
Each protection function has a trip counter. A trip
counter is reset to 0 whenever the compressor run
request is removed. Any trip that has occurred more
than 12 hours ago is removed from the trip count.
For some protection functions, when the trip counter
reaches value 3 (i.e. three consecutive trips occur) then
the unit is “locked out”.
When a unit is locked out the compressor is not allowed
to start. Lock-out is designed to protect the compressor
from repeatedly starting when a serious fault exists that
requires the attention of a service technician.
The display shows the code of the fault that caused the
lock-out condition.
A unit that is locked out can be unlocked using any one
of the following methods:
• Remove mains power from the unit for at least 3
seconds, then restore power.
• Issue an ‘unlock’ command via Modbus RTU serial
communications.
• Reset the controller via Modbus RTU serial
communications.
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