mitsu city multi

[philjd26]

hi, fit a few new parts to a pury-p250ymf-b r407c today, went to start system up and found no power to indoor controllers, ii was wondering are they powered from the outdoor in..?

rgrds phil

[Thermatech]

City Multi control communication daisy chain 30v d/c starts at the outdoor.

The outdoor unit must be powered up with 415v 3ph. Then provided no problem with outdoor unit control circuit you will get 30v d/c at all indoor units & remote controllers.
The remote controllers will have small dot on the display which indicates the controller has d/c power.

All remote controllers with an address connect to the 30v d/c daisy chain.
The basic controllers with no address work on 12v d/c & can only work if connected to the 12v d/c remote control terminals at the indoor unit, but almost no one uses this type of controller due to limited functions.

If you have no 30v d/c start at the outdoor unit with the control cable disconnected & measure at the M1 M2 terminals to see if the outdoor unit can supply the 30v d/c stand alone.
Then reconnect the control cable. If the 30v d/c voltage drops to less than about 27v d/c then there is a problem in the system like a dead short.

[philjd26]

thanks for reply thermatech,i have 30vdc at the m1 m2 ok, however its part of a network so i will try disconnect the contol cable tomorrow to see if it can supply 30vdc....another thing you seem to know mitsu well, can you visualise the inverter board that is located at the side of the elec box, there is a little coil of some sort that resembles a transformer below the invertor baord do you known what that is?

[martinw58]

if no power to indoor units controlers switch off after after about 30 seconds

[frank]

if no power to indoor units controlers switch off after after about 30 seconds
What happens then?????

[martinw58]

with no power to units thay dont run but system will not show a fault

[Thermatech]

Phil

I think that coil is a transmision choke coil.
The 30v d/c is made with components on the inverter board.

First make sure you have 30v d/c at the outdoor unit with the system disconnected at the M1 M2 terminals on the outdoor unit.
If thats ok trace the comms cable to the B/C box reconnect at the outdoor & disconnect the rest of the system at the box so that only the box is connected to the outdoor unit & see if the 30v d/c is ok at the box.
Then trace the cable to the 1st indoor unit disconnect the rest of the system & see if you have 30v d/c.
If you had no comms at any remote controller then this method should find the fault.
BTW what were the parts you fitted ?

If you have 30v d/c at the remote controllers but indoor units will not run then check for 240v at the indoor units & B/C box.

[philjd26]

hi
thanks for the reply, i i fit new transistors, inverter board, main board....i think i may have over looked something, so is the 30vdc come off thae diode stack somewhere and then passsed through a risistor or something?

[Thermatech]

The 30v d/c is generated on the inverter board which is powered up by 240v from incoming power.

You need to check out the other components like the large resistors & diode stack in the inverter circuit for the inverter to work.
But none of that stuf should stop the inverter board generating the 30v d/c for communication.

I have an old YMF test rig in the workshop for testing controls.
The inverter pack is stand alone on the bench & has the diode stack disconnected & 240v supply only to the red phase.
The inverter pack is connected to one indoor unit circuit board on M1 M2 which completes the system.
The inverter board & control board work normally & I can connect & test any remote controllers or central controllers.
The high voltage d/c part of the inverter circuit with capacitors, resistors, TRM's are all completely disconnected.
So I dont think that any other problem in the inverter circuit should be stoping the inverter board from generating the 30v d/c.
Often when you have an inveter pack on site which has just about everything blown to c--p the outdoor unit can still communicate with the indoor units & remote controls but will trip the power supply mcb at compressor start up.

BTW
There is no detail for the transmision choke coil in the service manual. But if you think it might be damaged you can test it should be about 1 ohm resistance disconnected from the board. If it is open circuit then you wont get any 30v d/c to the control board & out to the system.
But very rare for this component to fail.

[sighman]

Silly question, but is there power (230V) onto the indoor units?

[philjd26]

hi

school boy error left a connection out....

thanks again

[sinewave]

'We' knew that but didn't like to say! :D