Mitsubishi VRF Fault

[marc5180]

I was sent to a site today that we look after to carry out routine manintenance on their AC. When i got to site i noticed that there are 3 seperate VRF's which each control 1 floor (3 floors in total). Model number of condensor PURYP300
The G50 controller was flashing 1102 on floor 2's condensor. I reset it, then went up to the 2nd floor and found most of the controllers flashing with the fault 1500.
I found out these mean overcharged and discharge super heat is less than 10 deg C.

I went onto the roof to look at the controller and looked at the discharge sensor TH11 and checked the resistance of this, which seemd to be fine. The discharge seemed very hot to touch but the suction was also cold and sweating. I connected my guages and the pressures/temps seemed fine.
The discharge was 28 bar which was around 48Deg C with a discharge superheat of around 30k.
the suction was at 6.5 bar, 0.5Deg C but had a superheat of 0k.

I went to ask the manager about it and he told me they had, had a power cut earlier in the week which took out the whole of the building's electricity for over 4 hours and hasn't worked since then.
I think for some reason that the outdoor unit isnt talking to the indoor units so i want to do a virgin restart tomorrow but i'm not sure i remember how to do it correctly.
Am i right in thinking i should Power down condensor, all indoors and BC box, then SW 2, switch 2+3 on.
Then power up outdoor, wait until "1" is displayed on the led display on outdoor PCB then power down and put dip switches back, wait 20mins the power up indoors then outdoor then bc box. Thats how i'm thinking i should do it but it's been a while since i have done it.

If they have lost their address settings then am i right in thinking thsi could cause the 1102 and 1500 fault?.

Also the manager says they have frequent power cuts in that area so will i have to keep going back each time they have a power cut to readdress them?
And lastly why have all of the condensors not lost their address settings ( if thats the case) and are working fine even after the power cut?

[Thermatech]

Marc

1102 is for high discharge temp over 120 deg C 3 times within 30 mins.
that means very high discharge SH. So suspect SOG.
1500 is very low discharge SH less than 10 deg C. So suspect overcharge.

The system cannot be overcharged & undercharged so something is happening in the system to limit the suction flow back to the outdoor unit sometimes & then suddenly allows the refrigerant flow back again & overflows the suction accumulator.

Once the address settings are made on the dips all units will do an electronic hand shake again after a power cut so that should not be a problem.

But the lev valves at the indoor units might not have reset to shut datum point at power up after power cut.
This could cause the faults you have because when an indoor unit is not cooling the indoor unit & gas tube back to B/C will fill up with liquid & make system look SOG but when the unit starts cooling & B/C suction solenoid valve opens all that liquid suddenly floods back to the outdoor unit so it sees overcharge.

So power down everything including the B/C box then do the virgin restart.
The virgin reset procedure you describe is good.
Dont bother with the 20 mins, when the display goes blank after power off is good enough & then power back up. You just need to let the capacitors drain down so there is no voltage on the control board before power up again.
The power reset of the indoor units should force the indoor unit LEV valves to motor open / shut & so find the datum shut possition again.

But it can be important to get the power up sequence correct because each indoor unit have to do an electronic hand shake with the B/C box so that it will open & shut the solenoid valves for that port when requested to by the indoor unit.

Normally I would power up
1/ the indoor unit first.
2/ The B/C box second.
3/ The outdoor unit last.

I have always found this to work when there has been a communication problem between the indoor units & B/C box.

but

latetly mitsubishi tech help have been suggesting indoor units then outdoor unit & B/C box last.

Anyway when the indoor unit are not properly communicating with the B/C box there is no fault code indication but the B/C does not open the solenoid valves in responce to the indoor unit calling for cooling or heating.
On some rare occations this can happen & in this case might have been due to the power cut.

To finish off I would test each indoor unit in heating & cooling to confirm indoor unit lev & B/C port solenoid valves all working correctly.
Only run 2 units at each time 1 in heat & 1 in cool then switch them off & move on to the next 2 units & do the same again.
I know it takes a while but its the best way to be sure the units are working correctly.

[marc5180]

Yes that's what confused me, SOG but then overcharged as well. I am going back first thing so i will let you know how i get on. I am hopefull that that is the problem, still don't understand why it may have wiped the field settings.

Can i ask though how you know so much about mitsubishi kit? Do you work for mitsi or do you just have lots of experience with their kit cos' you certainly know your stuff.

I went to give you reps but it wont let me, it says i must spread it around before giving it to you again.

[marc5180]

Ah ok so thats why:)

[marc5180]

Just to update you, i went back to the unit today and carried out the virgin restart,, which didn't work:confused:

Checked the bc box and tried a valve reset, which had no effect, also tried a valve reset on some of the indoor units which again made no difference. Checked the 4 way valve was switching and was not jammed.

After we had tested the 4 way valve, all 7 indoors were set on heating, we went to each indoor unit and were surprised to find 40DegC coming off each unit, so we switched over to cooling but we only seemed to be getting maximum 4K across the coil. with the lowest air of at 19Deg C.

We found one or 2 units trying that seemed to be trying to cool , so we stripped them down to take a look at the Lev going into the evap coil and found that it was icey cold but it didnt seem to travel the whole way across the coil, it only seemd to get about 1/6th of the way across the coil, hence why we were getting no cooling.
We started to check each indoor unit and we came across a ducted fan coil that was hidden away but we didnt really have access to it apart from turning power off to it. We found this unit making a lot of noise but... we were getting 12Degc air off. We were going to strip the unit down to have a look at the Lev but there was no access.
We managed to look in the electrical box for the Lev plug and wefound it hanging loose, so it wasn't connected:D. We plugged it back in but then realised we would have to do a virgin restart again. We did this and as we were getting ready to leave we could only stay with it for 10mins but each indoor unit was cooling:D. We aer back tomorrow to check it though and carry on with the manintenance.
So what must have happened is that the Lev was fully open and this was in effect pinching the liquid from the other units.

This can't have ever worked from day one even though people swear blind that it did. Just glad it sorted, i think:D

[Thermatech]

Liquid bypass to suction on that ducted unit when unit requesting cooling & suction solenoid valve at B/C open.
You could hear the refrigerant flooding through the coil ?
All other units will have poor performance due to the bypass at this unit.
If the room temp ever gets to set point for this unit then the suction solenoid valve shuts but because the indoor unit LEV is still open liquid refrigerant fills up the coil & gas tube back to the B/C box. This can be a lot of refrigerant volume trapped in this unit & makes the system look SOG.
When the unit starts cooling again & the suction solenoid valve at the B/C box for this port opens then all that liquid floods back to the outdoor unit & can overflow the suction accumulator making low discharge SH.