Mitsubishi MXZ series serial communication error

Jerry323

I have a MXZ3C30NA2 outdoor units servicing two MSZ indoor units. All has worked well for six years. Woke up week ago to cold house area served by these units. Upper operation LED on inside unit flashing constantly at 0.5 second rate. Neither the outside or inside units running.

Performed failure mode recall on one inside unit and it indicated communications error (did not receive signals from outside unit for six minites (three flashes/beeps with no three second light before flashes). Repeated the procedure with remaining indoor unit with same results.

Went to outdoor unit- LED1 and LED2 constant on no flashes, LED3 flashed 10 times then repeats. Voltage measurement and both connected indoor wiring blocks show 240 volts S1 to S2 and constant 10.4 volts between S2 and S3 (no fluctuations indicating no data. With no connections to the open third indoor unit connection block S2 to S3 shows 14 volts.

I cant believe both indoor units failed simultanously. Does anyone know of any additional troubleshooting I can do to further isolate the issue.

I really appreciate the group's input. All the best.

pecmsg

Contact Mitsubishi Tech Support

109A_5

Hello @Jerry323,

Jerry323 said:

I cant believe both indoor units failed simultaneously.

With that type of failure I would suspect the outdoor unit. However the manual troubleshooting tree would lead you to believe that both indoor units failed. Did you cycle the power on all the units ? Leave them off for at least a minute.

Document Page 74
https://www.theacoutlet.com/documents/Owners-Manual-Mitsubishi-MXZ2C.pdf

Jerry323

109A5: Yes, have cycled power several times. Still same, no operation.

Yes, I will try and get Mitsubishi to talk to me.

Thanks!

109A_5

Hello @Jerry323,
If you have not, one at a time I would disconnect the S3 wire from the indoor units at the outdoor unit, then cycle power. It may be actually be a 'Party Line' and one of the indoor units is jamming up the communication.

Check fuses on the circuit board, may be more than one.

skimberk1

Hey! I’m having the exact same issue with my Mitsubishi mini-split (although in my case it’s a mxz-3c24na2) and was wondering if you were able to figure out what happened/how to fix it! Everything is identical to how you described it:

indoor unit flashing on/off constantly, failure mode indicates signal error (three flashes/beeps), outdoor unit- red LED1 and yellow LED2 constant on no flashes, green LED3 flashed 10 times then repeats

I have three indoor units connected to the outdoor unit, and also have a hard time believing they all failed at the same time.

Thanks so much!

GW

seems like the outdoor unit’s board isn’t sending comm- likely needs to be replaced

pull the S3 connections outside and measure DC between terminals S2 and S3. If it’s not bouncing, board needs replacement.

If it is bouncing, put S3 wires back on and now check indoors (S3 wire is disconnected indoors). if it’s going up and down, wire is good.

Yes- unlikely both indoor units would fail at the same time

GW

one more thing- when in doubt always kill power for 5 minutes minimum. Restart

we had a job recently where comm was lost for no apparent reason. That was unusual