Mitsubishi AC Unit MODBUS Control, Not Able to Write to Settable Control Registers

Hello,

I am trying to use an INMBSMIT001I000 converter to remotely control a Mitsubishi MSZ-FS06NA AC unit via MODBUS from an AutomationDirect BRX PLC. I have this wired up and working in software for the majority of reads and writes to the AC unit, but when it comes to what I actually need to control for my application - fan speed - the AC unit does not accept writes and remains at fixed fan speed (4/high).

Per the compatibility tool, this AC unit shows as compatible with the protocol converter.

I do not get any MODBUS errors as read via the BRX PLC (in AutomationDirect's Do-More Designer software)r

I am able to write external temperature reference via the protocol converter to the AC unit, I am able to turn the AC unit on and off, I am able to change its mode (auto/0 through cool/4), see operation time incrementing, no error codes or alarms active, and the remote control is enabled.

But, the AC unit does not "accept" writes to PLC register 3 for fan speed - no matter what is written to that register (0 through 3) it remains 4/high when read back.

Also, the max number of fan speeds register (PLC add 22) reads back 0, which is consistent to the DIP switch settings on the protocol converter and the default (unit has 4 fan speeds and auto mode), so I know I should be able to change this as desired.

Can you help out with what I might be missing to control fan speed via the protocol converter tot this AC unit?

Thanks.

Kyle Reynolds

March 14, 2024 16:58

Hi Daniel,

Have you set the dip switches to set the correct number of fan speeds?

See User Manual (page 13).

Daniel Worts

March 14, 2024 17:07

Yes, all DIP switches on SW1 are in the OFF position, and the register (plc reg 22 read only) reads back "0", which is consistent with the hardware setting and should be consistent with the default "AC indoor Unit has 4 fan speeds and AUTO (Default value)".

March 14, 2024 20:24

This is unusual. Everything seems to be configured correctly. I will have to create a support case to escalate this to the Intesis engineers. You will get an email with the case number.

Mitsubishi AC Unit MODBUS Control, Not Able to Write to Settable Control Registers

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