Adding another indoor unit to a City Multi

[In-My-Van]

I had a query from a customer today. They have a Mitsubishi City Multi supplying 7 indoor units via a BC box. They wanted to know if the spare stub on the BC box could be used to add another indoor unit. I am planing a site visit and am running through my mind whats required. I will need to see what KW of indoors are connected and compare this to the KW of the Outdoor unit and i will also have to see what the required duty is for this extra airconditioned space.
Is there anything else i need from a sizing point of view?
I am also unsure how to reconfigure the M-Net to "see" the new unit. Any pointers?
I did the Mr Slim Mitzi course a few years back and have repaired and maintained City Multi's for some years but i have never been asked to add another unit so any help would be much appreciated.

[AbsoluteWDJ]

I had a query from a customer today. They have a Mitsubishi City Multi supplying 7 indoor units via a BC box. They wanted to know if the spare stub on the BC box could be used to add another indoor unit. I am planing a site visit and am running through my mind whats required. I will need to see what KW of indoors are connected and compare this to the KW of the Outdoor unit and i will also have to see what the required duty is for this extra airconditioned space.
Is there anything else i need from a sizing point of view?
I am also unsure how to reconfigure the M-Net to "see" the new unit. Any pointers?
I did the Mr Slim Mitzi course a few years back and have repaired and maintained City Multi's for some years but i have never been asked to add another unit so any help would be much appreciated.

I think you already know what you're looking out for. Don't oversize the indoor capacity to existing outdoor. Make sure there is an additional port on BC. Make sure that the address of the proposed additional unit doesn't conflict. I.E there is not another unit with the same address on a central control. Other than that....Plan sailing!!

[martinw58]

dont forget the m net need to be daisy chained dont just take a wire from one unit to the new unit and address the unit to the port number on the bc unit

[install monkey]

make sure the indoor equivalent is available- cannot get a 410a compact cassette for a ymfc . and by the time you degas it,connect into the bc box, pressure test,vac,calculate the additional charge and allow for the extreme cost of an indoor, it may be cheaper getting an m series split and sticking a mac interface to connect on the m net and allowing the central controller to control it/timer function

[regcooldude]

dont forget the m net need to be daisy chained dont just take a wire from one unit to the new unit and address the unit to the port number on the bc unit
And don't forget to do a virgin re-start at the condenser once you've addressed the new fan coil.

[stufus]

The M-NET can be spliced anywhere so long as polarity is maintained.:cool:
And taking a wire(cable) from one unit to the new unit is a daisy chain;)


dont forget the m net need to be daisy chained dont just take a wire from one unit to the new unit and address the unit to the port number on the bc unit

Cheers

Stu

[JoeAT50A]

make sure the indoor equivalent is available- cannot get a 410a compact cassette for a ymfc . and by the time you degas it,connect into the bc box, pressure test,vac,calculate the additional charge and allow for the extreme cost of an indoor, it may be cheaper getting an m series split and sticking a mac interface to connect on the m net and allowing the central controller to control it/timer function
I agree with IM, however please check your total capacity of indoor units should not more than 150% of your outdoor unit's capacity. And also check whether available an additional port on BC or not. If there no extra room then, solution will too expensive and try to get M-series with Mnet interface MAC-399IF or MAC-333IF instead.