City Multi issue

[Daz man]

Hi all,

I have being having issues on my 2001 R407c Mitsubishi City Multi system where certain indoor units, a mix of wall and cassette units don't seem to be cooling as required. They are doing a bit, however not biting cold like I would expect. Then a couple of indoors work brilliantly.

outdoor is a - PURY-P250YMF-C
BC controller box is an eight way - CMB-P108V-E

I've spoken with Mitsi tech and filled out the dip switch diagnostic sheets to be told that TH15 & TH16 in the box need replacing with new thermistors. Done this but still the same.


dont know if this helps but I have found that the pipe coining upto LEV3 of the BC controller box has formed Ice (see pic)

any thoughts anybody, Install Monkey you're the man?

[install monkey]

get 2 spanners on and slacken off the lev head- like a trv on a radiator- make sure u use a 14 and 17mm open end spanners- not bachos or grips- either lev head worn - not opening or pin jammed on body;)

[Neddy]

Lev 3 is only used for sub cooling in cooling mode. Looks like LEV 3 is flooding liquid back to the City Multi. A low suction temperature at the city multi will confirm this. If so replace LEV 3.

[Daz man]

Cheers both. Good advice on spanners. Typically the BC box is in a ceiling void above servers (fire proof) ceiling with hardly any access hatches. I can just about access the side of the box where LEV3 is situated. Why do install engineers install these BC controller boxes in places hard to maintain further down the line in years to come? Pet hate!
Am I okay removing the head whilst it is charged? Are they like the LEV heads on an indoor cassettes where the heads come off a plunger type pin so no refrigerant escapes?

[install monkey]

yep you can remove it under normal pressure-best to do it whilst in cooling demand- as you turn the head off you should hear an increase in pressure as you loosen it- if pin jammed the noise/flow wont increase so it will prove pin jammed- only thing is they are a b**tard to get back on you need arms like popeye or be like me- blessed with mong strength!:D

[Daz man]

Update -

spoke with technical today, who TBF have been quite helpful. They suggested that I firstly remove the head off LEV 1 as there was a 20oC difference between TH11 and TH16 (starving the system of refrigerant). After stripping the bc box back by removing the electric box side, LEV 1 is quite easy to access. Using a 19mm and a 17mm open ended spanners removing it was pretty straight forward. Technical explained that the valve is hermetically sealed so even if fully charged refrigerant won't escape (still apprehensive at the time, but all good no loss of refrigerant at all). I did notice a slight improvement re cooling duty off my 8 indoors however still not perfect. Technical then suggested, that due to age of the City Multi it would be a good exercise to change LEV 3 at the same time as LEV 1 (same part number as it happens). Question? LEV 3 controls the sub cooling levels is this correct and if I was to remove the head of LEV 3 off the body as a temporary exercise would this prove anything by improving my cooling capacity off all indoors?

hope this helps all, just thought I'd update this post?

[Neddy]

Removing the head of LEV 3 will reduce your cooling capacity as most of the liquid will flood back to the City Multi starving the indoors of liquid.