Trane TVR Pro CO Series Service Manual page 92

2.16 yHd: Slave unit malfunction
Digital display output
In the error code, 'y' is a placeholder for the address (1 or 2) of the slave unit with the error.
Description
 1Hd indicates an error on the slave unit with address 1.
 2Hd indicates an error on the slave unit with address 2.
 All units stop running.
 Error code is only displayed on the master unit.
Trigger / recover condition
 Trigger condition: Slave unit is malfunction.
 Recover condition: Slave unit goes back to normal.
 Reset method: Resume automatically.
Possible causes
 Slave unit malfunction.
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