Mitsubishi vrf leak test

[airconadam]

Hey fellas i wanted to know what the best way is to test a vrf is sog the only reason for asking is i got called to a mitsi vrf the other day,it has 10 units on the system when i put all 10 units on test cooling the indoor units have an air off of between 17 and 21 deg c if i turn one of at a time the other units then get better at cooling,i ran only 3 units on test and they were cooling fine i have done this before and when reclaiming refrigerant it has been sog but i would like to know what other better ways there is to check?? much appeciated

adam

[Fri3Oil System]

Hey fellas i wanted to know what the best way is to test a vrf is sog the only reason for asking is i got called to a mitsi vrf the other day,it has 10 units on the system when i put all 10 units on test cooling the indoor units have an air off of between 17 and 21 deg c if i turn one of at a time the other units then get better at cooling,i ran only 3 units on test and they were cooling fine i have done this before and when reclaiming refrigerant it has been sog but i would like to know what other better ways there is to check?? much appeciated

adam

Hi, here in Spain, many companies are starting to do a pressure test with vaccuum first, check with an ultrasonic device, and then charge with nitrogen, and check again with the ultrasonic leak detector. This way, the pressure test is carried out in a very short time.

[Gingerair]

Re-measure all system pipework & calculate total system charge..
Decant system & compare ammounts..
If short, press test, repair & re-commission..

As i understand it, due to diversity you may not get good cooling delta-t's if all indoors are in test cooling.

There are many other reasons why system performance maybe lower than expected..

You have not stated what system you have, R2 etc..

Thermatec is probably your man though..

[El Padre]

Refrigerant shortage should be more evident with the units under test in Heating mode, regardless of which mode you test them in, monitor discharge superheat as it will be inversely proportional to the system charge.

Cheers

[Brian_UK]

Check the diversity before pulling any gas charge out.

[Thermatech]

There are a number of key indicators for SOG on City Multi
To some extent it depends what model & what refrigerant.

If you look in the service manual you will find some cooling & heating operating data which points you in the right direction.

1st check pipe lenghts as very long pipe lenghs reduce performance due to pressure drop.
2nd check total capacity of indoor units connected. If over index then the performance will be reduced when all requesting max performance & outdoor unit can only ramp up to 100%

If thats all ok then monitor the outdoor unit using SW1 & display.
Look at compressor speed , HP , LP & compressor discharge temp & calculate DSH.

If the discharge temp keeps hitting max & the comp ramps down to lower the discharge temp & then ramps back up & hits max then you can be sure the system is SOG or some other problem which is reducing refrigerant flow back to outdoor unit.

As you have found sometime there is just enough refrigerant in the system to give ok performance when only a small number of indoor units operating because comp does not need to ramp up to high speed so enough suction gas volume to keep compressor motor cool & discharge temp stays below max.
So when SOG really becomes noticeable like you have seen is when the compressor has to back off due to max discharge temp.

There are many other things especially with R2 heat recovery systems which can cause poor referigerant flow & the system can look sog but its not really. But if you can prove good performance at the indoor units by running 2 or 3 at a time & find good performance at all indoor units then for sure suspect SOG & proceed to recover refrigerant.

Let us know the Outdoor model

[airconadam]

Hey guys thanks for all the replies sorry not got back to you earlier been away from home,great info, the model num is a pury yhm model not sure if it is a 200,250 etc i am going to site tomorrow and will have a look at all those things mentioned, i have got the green service booklet but i don't seem to get some of the figures mentioned in the book, soon as i get home tomorrow i will keep you updated thanks once again.

Adam

[airconadam]

Went back to site today and put all 11 indoors on heating. After 30mins i checked back on the G50 controller and all of the rooms had risen to between 25-27C.

I then switched all indoors onto cooling but didnt get much cooling around 18-23C air off.

I checked on SW1 data and found discharge temp at 70C with discharge superheat around 22C, the frequency of the compressor was around 70hz and the condensing and evaporating temperatures were at the target temps ( 39C and 0C )

I checked through each indoor to be sure the LEV's were working and also on the BC box and they were all fine, they were controlling the superheat or fully open as they should be.

I then decided to put a few units on at a time and watch to see if the capacity dropped and sure enough after i had put on 6 indoors the cooling dropped off from all indoors.

I would have expected the compressor to be ramping down due to the high discharge temp normally seen when a unit is short of refrigerant but this isn't the case.

Is there anything else i should be looking at Thermatech?

BTW the outdoor is a PURY P300YHMA and the index of the indoors are 355 so diversity is 118%, so well within.

[Thermatech]

I tend to find the outdoor unit will run in cooling at 24 bar discharge & arround 7.5 bar suction. So if the system is running arround this pressure & 70degC discharge then it does not look SOG.

There are lots of other things which could result in poor cooling performance.

1/ Try looking at the SC16 & SH12 at the BC box as this will give an indication of the subcooler performance.
Good subcooler performance is very important for this system to have correct cooling performance.

2/ Also look at the superheat data for each of the indoor units. If the SH is high then suspect poor refrigerant flow through indoor unit LEV or blockage at indoor unit liquid line strainer.

3/ If one indoor unit has locked fully open LEV valve then this can make the system look SOG.
When the indoor unit is cooling then liquid refrigerant will bypass through this indoor unit & make poor liquid flow at the other indoor units.
When this unit is stopped the LEV is locked fully open but the gas line solenoid shuts at the BC on the port connected to this indoor unit & so then liquid floods into this indoor unit coil & the suction tube all the way back to the BC. This effectively traps a large volume of refrigerant which in turn makes the system look SOG.

[airconadam]

Sorry for not replying sooner,we went back to site a few days after and was told by the guy on site not to bother looking at it due to it being under warranty still by the installers .When we probed further into it they have had previous problems with the system from day one of it being installed!! We looked at their worksheets which said they were unable to find a leak and had put uv dye into the system to find a leak

Adam.