City Multi PURY-250YGM-B 4210 error

[Joelad]

Hi lads, would just like to bounce this off you and see if you've any ideas

Working on a city multi unit as above, which is throwing up error 4210 (breaking over current). When i came to unit found breaker was down so reset it and hooked laptop to g50 to find a history of breaking over current in malfunction log.

Turned all units into cooling and waited at outdoor unit to see what happens and unit went straight out on 4210. Initially thought it was inverter board so swapped it out with one i knew was ok but that made no difference. I then disconnected compressor cables from terminals and reset unit just to cancel out the compressor being mechanically seized and also to ensure equal voltage from each phase to neutral and earth. While measuring the voltage i was getting peculiar values of 50 to 70 to 130volts to 200volts every time i put my probe on each cable. There were no steady figures.

All i can think of now is that theres a problem with the transistor modules. Finally to the point, could this be possible based on what ive found? and how do i check these? Just thought id throw it out there and see if any of you had any thoughts on it.

[Thermatech]

Confused about the outdoor model you are looking at because it does not match the 4210 fault code.
The older R22 & some early R407c units with TRM's had 4210 overcurrent fault code.
Then Mitsubishi like the other manufacturers moved on to IPM inverter component & the overcurrent fault codes changed to 4240 & 4250 so R410a systems like YGM-A dont have a 4210 fault code listed in the service manual.
So I suspect you have older model with 3 TRM,s(transistor relay module) in the inverter pack.

Anyway whatever model you are looking at
1/ Did you check 3ph power supply to outdoor unit? Important to have ballanced 3ph & no voltage on the N line.
2/ Did you test compressor motor windings ohms & Mega test windings.
If any 1 winding has ground fault then 4210 or trip MCB.
3/ On some models you need to set dip on inverter board for disregarding low amps & then test for ballanced inverter output with compressor disconnected.
Any which way you measure should be ballance U-V-W to E or to N should all be same voltage or U-V , U-W , V-W also should be ballanced.

One thing that can happen in very cold ambient is that when you turn on the outdoor unit power supply the outdoor unit first goes for compresssor warm up mode . The inverter supplies some voltage to the compressor on two windings so the compressor does not rotate but the windings warm up & this warms up the oil.
So good idea to check outdoor air temp sensor data to be sure it is reading warmer >10 deg C to be sure compressor warm up mode is not comming into play.

If you still have un ballanced supply from inverter then you can confirm the location of the fault by taking out the TRM,s or the IMP & do a number of resistance checks.
While you are doing that you can also check the other inverter circuit components like diode stack, resisters, capacitors, contactor ect ect.

I will not try to explain how to do this but it is covered in the service manual.

BTW
Be carefull swapping the inverter circuit board before you have located the exact problem as you risk damaging the replacement circuit board.
Always make sure the capacitors have discharged before working on the inverter circuit as there is some very high voltage for a few mins after power shut down.

[Joelad]

The unit in question is an r22 older model. Initially i checked the 410a service manual which as you said does not have the 4210 error code but when i hooked up the mnet service tool and checked the malfunction log it threw the error at me.

Cheers for the heads up on the capacitor discharge but i left units isolated for 20mins before attempting the swap.

Turns out it was the TRM's, i took them out and replaced them with TRM's from another unit and it then ran away perfectly. Have new ones ordered. Thanks for replying