Mitsubishi city multi

[airconadam]

Was sent to another one of our sites today with 2 Pury p300 yhma joined together feeding 30 indoors,maintenance guy on site said various rooms seem not to cool then they will cool for an hour or so and have been doing it for a few days now,after looking at the G50 no faults were in the history.After my last post with the SOG situation i tested a few things as per previous post i went through all the liquid inlet temps and gas temps to each indoor aswell as (SH) readings,i made sure all the units were on test run cool and were all being called for by checking the sw1 data,the inlet temps were between 5degc and 7degc and gas varied between 15dec to 24degc depending on the heat load in the room?? i then found one unit which had an inlet temp of 25.5 and a gas temp of 25.6!!! I double checked all the units were still being called for and on test run.I then checked the lev opening for the unit which was at 155 pulses ,so it was trying to close the valve. I am now wondering if this system is struggling due to the evap being flooded and the pipework full of liquid? but also would one evap doing this cause such a problem?? The indoor unit was a pefy p25 vmme, also the diversity is 115% so that is ok.I also done an lev reset but still the unit was doing the same.

Thanks alot

Adam

[Thermatech]

Do you think coil temp sensors TH2 =25 & TH3 =25 was warm liquid flushing straight through the indoor unit
or
LEV valve locked shut & both coil sensors reading room air temp.

LEV @ 155 is ok for indoor size 25 at max it will only open to about 300 in cooling because its very small unit & will be ramping up or down in responce to the SH reading. For normal operation it migh ramp down to about 110 if the SH is low.

You need to inspect this unit to see.

Hotel ?
2 BC boxes ?
Branch address for all the indoor units correct ?

If complaint was some rooms intermiitently not cooling suspect incorrecty branch address settings.

Suggest prohibit local remote controllers with G50 setting & then run all units in test cooling & one at a time run one in test heating & confirm hot gas at correct indoor unit.

Other possibilty could be solenoid valves not opening due to failed soilenoid coil at BC box for one or more ports.
If cooling solenoids A & C dont open for cooling operation but the indoor unit LEV opens then the indoor unit & gas tube back to the BC just fills up with liquid. This traps some liquid & can make the system look SOG.

But if one indoor unit has locked open LEV valve then you get high to low bypass through that unit with lots of liquid flushing through it. That reduces liquid available for other indoor units so poor cooling performance.

[airconadam]

Thanks for the quick reply thermatech,What should the superheat be 5degc/10degc, also when i was checking lev 1 and 2 in the bc boxes on cooling only/main they should both be fully open at 2000, which they was,but i then rechecked after a while lev 2 was not at 2000???? but at 200!!! after 5 mins it went back to 2000 any reason for this?? i also checked that valves A and C were open aswell,which they was also. SH was at 0 for this unit, this system is in a care home similar to a hotel.I locked out all the controllers so no one could mess with the controllers,and yes 2 bc boxes, even with the unit turned off it can fill with liquid????

much appreciated

Adam

[Thermatech]

1/ generally BC box LEV 1 & 2 will both be full open @ 2000 for cooling only mode.
2/ SH of 0 at indoor unit due to Th2 & TH3 both reading almost same temp.
Unit ramps open / closed LEV to maintain target SH value. This value depends on model & size of indoor unit but will normally be in the 6 to 9k range. If overshoot target below 6 then LEV will ramp down little by little. If not able to achieve SH target then LEV will ramp open little by little untill enough refrigerant passing through coil to achieve target.
3/ If the indoor unit is in cooling mode & has locked open LEV valve & BC valves A&B or both energized for suction valve open then lots of liquid refrigerant flooding through indoor unit back to suction.
Then unit is switched off at remote controller or 240v power. LEV does not shut because it is mechanically locked bur BC solenoids A&B de energized & suction valve closed. Indoor unit & suction tube back to BC fill up with liquid.
The liquid line is always live to the indoor units, no other valves in liquid line. At the BC box only check valves to control liquid flow through subcooler.