Trane TVR Pro CO Series Service Manual page 58

2.2 E0: Communication error between outdoor units
Digital display output
Description
 Communication error between outdoor units.
 All units stop running.
 Error code is only displayed on the slave unit with the error.
Trigger / recover condition
 Trigger condition: Slave unit cannot receive signal from master unit for 60s.
 Recover condition: Slave unit can receive signal from master unit.
 Reset method: Resume automatically.
Possible causes
 Incorrect outdoor unit address setting.
 Communication wires between outdoor units not connected properly.
 Loosened wiring within electric control box.
 Damaged main PCB or electric control box communication terminals block.
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