Research Concepts RC1000 - Manual (Page 43)

If the AutoPol feature is enabled and the command parameter is 'H',
'V', 'C', or 'W' the NAK reply will be sent to the host.
byte 0 : NAK
byte 1 : 'AA' where AA is the RC1000A address
byte 2 : '34h' the command code
byte 3 : ETX
byte 4 : 'chksum' the checksum
If the command can be executed the reply to this command will be the
same as the reply to the QUERY command except the command code will
'34h'.