Mitsubishi City Multi PURY-P250 YMFC R407C

[mick5]

Hi,
Would be grateful if could advise or had any experience of the following problem on one of these systems.
I have inherited a site with two PURY P250 YMFC systems. One system has five under ceiling fan coils of different sizes connected to a BC box on the first floor.
One of the under ceiling units a PCFY P40 VGMA is in a server room and not cooling. The other four units are all heating. There are no fault codes so I tested the system pressures and found that if one unit was cooling and the others heating it had 3 bar low pressure 16 bar high with just the server room cooling and all others off it was 2 bar at a 2oC ambient. Just for reference the other ground floor system had 3.7bar low pressure and 18 bar high with one cooling and all others heating.

I have re set the LEV by disconnecting it and powering the indoor on/off. This then gave a little cooling off the fan coil but only on the right hand side. 14oC off on the right and 24oC on the left, the air on was 28oC. Later that day the unit then stopped cooling again.

Went back and tested a unit in another room set that in cooling and all the others in heating this unit also had a difference across the coil 12oC off on the right and 21oC on the left. Checked what was happening at the BC box and started to feel cold pipe off the BC box but the faded away. The suction from the BC box was not sweating back or feeling cold.
I have a feeling its low on gas as there was quite a bit of noise from the pipes going into the fan coil when it was trying to cool after the LEV re set.

Spoke to Kooltech Mitsubishi Tech who have been very helpful and they seem to think it could be the main LEV3 in the BC box or short of gas. They said the LEV motor last about 8 years and the units have a date stamp of 2003 making them 6 years old.

Just wondered if any one else had had the same problem as we are going to recover and leak test anyway just wondered if we should change the LEV on the BC box too if it is easy enough.
Many Thanks

[Thermatech]

The system has been running 24/7 since 2003 for the sake of the one indoor unit in the server room.
So the system will have massive run hrs & the LEV valves have spent all that time motoring open / shut so they are likely to be worn out.
Out of interest do the SW1 dips for the run hrs & see.

The thing with these systems when they have done mega run hrs is that there can be a number of problems which are contributing to the poor performance.
You need to eliminate one at a time. After resolve one major problem then its easier to see the smaller ones which were hidden behind the major problem.

LEV 3 in the BC box is always prime suspect as it controls the flow of refrigerant through the subcooler.
All warm liquid coming back to the box from the units which are heating has first to go through the subcooler to eleminate the bubbles & then the liquid can go to the indoor units which are cooling. Any excess liquid gets dumped back into the suction & goes back to the outdoor unit through LEV 3.In this case we expect to see very cold suction pipe as it is effectively extension of the outdoor coil (evaporator )in heat main mode.

In your case the suction is not cold at the box so the system is SOG or very poor refrigerant flow through LEV 3.

The refrigerant flow through the indoor unit in the server room is also suspect due to the very low pressure when you ran that unit only in cooling. At that operating condition LEV 3 operation not so critical as all liquid is going through the one cooling unit & back to suction. Would expect to see about 5 bar suction not 2 bar only.


A good place to start is remove the refrigerant charge to see if it has full charge.
But before you do that remove the LEV 3 motor head to be sure you get full bore liquid flow with it fully open.
Sometimes the poor refrigerant flow is due to blocked strainer in liquid line just by the LEV3 so you need to see that its not blocked before you remove the refrigerant charge.

The system is operating with very low suction pressure at all running conditions you have reported & the discharge temp will be very high. The outdoor unit will protect its self by reducing compressr speed & this makes poor performance.
So the system could have a full refrigerant charge but the refrigerant is just not getting back to the outdoor unit on the suction & you need to find out why.
or
the system is SOG
or
a combination of both.

BC box solenoid valve operation is worth a check as refrigerant wont flow through a solenoid valve with failed solenoid.

There could be refrigerant flow or bypass problems at the outdoor unit.

Starting with a full charge of refrigerant is always helpfull as you dont then have to consider that it could be part of the problem & you can then concentrate on finding the cause of poor refrigerant flow.

[mick5]

Hi,
Thanks for your comprehensive reply, really appreciated. Looks like you have probably forgotton more than I know!!.

Can I just double check part of what you said below.
"A good place to start is remove the refrigerant charge to see if it has full charge.
But before you do that remove the LEV 3 motor head to be sure you get full bore liquid flow with it fully open.
Sometimes the poor refrigerant flow is due to blocked strainer in liquid line just by the LEV3 so you need to see that its not blocked before you remove the refrigerant charge".

I guess you are saying to remove the LEV3 motor head and then run one unit in cooling with all others off to see if I get a better suction pressure before recovering the refigerant.

Many Thanks
Mick

[Thermatech]

Yes

Just remove the motor head.
Sometimes the reduction gearbox fails at locked shut.
Or
The strainer just before the LEV 3 is blocked with contamination.

This problem will cause low suction pressure & therefore make the system look SOG.

If you can see frosted liquid tube after the strainer then the strainer is partially blocked.

If when you start to undo the LEV 3 head liquid starts flooding through as the needle moves up out of the seat then there is a good chance that the LEV valve head is locked in a shut or near shut possition.

At 2 bar suction the discharge temp & SH will be excessive & the compressor will ramp down & might also bypass at the outdoor unit.

But if opening up the LEV3 does not make any difference to suction pressure & no indication of blockage at strainer then system is most likely SOG.

So a quick check of the B/C box could save you all the time to recover vac & recharge the system.

If you have the service manual & do the SW1 dips for the temperature sensors & pressure sensors you can see all the live data which you could see on the service monitor computer & that can help you to see what is happening in the system.

A good standard check is all the pressure sensors at the box & the outdoor unit with the compressors at stop to see that they all show the correct standing pressure.
then
watch the suction & discharge with your gauges connected to confirm correct discharge & suction pressure data as the compressor ramps up.

[sexysouthwest]

If you need a service manual i can email you one.

[mick5]

Hi,
Thanks for the extra explanation. We will try that when we go back. They are coping at the moment with a couple of portable units and have given the go ahead to install a split sytem for the Server room as a back up. Cant do this till there break in Half term when we will be able to service and check the whole system.

Thanks for the offer of a manual. I think we have one that Kooltech sent us. Many Thanks Mick.

[mick5]

Hi, Sorry i have not replied about the outcome of this problem but we have not been able to go back to site yet. We carried out your tests on the system when we went back to install a split in the server room and found that opening up the LEV3 made a diffrence to the pressure.
We have got one to fit but they found asbestos in the place when we were installing the split so can not go back till its removed at the next school break. Will let you now the outcome. Thanks Michael

[mick5]

Hi,
We have ben back and changed the LEV3 but it made no diffrence. The sytem has now got a 056-1102 fault code logged which we have been told by Mitsi is a low refigerant fault which would be right as it was about 1.5 bar at its lowest and nearly 4 bar with the LEV3 open. Now going to recover, pressure test etc and re charge. At least we ruled out the easy option of the LEV3 valve. Thanks Mick

[marc5180]

Thanks for updating us Mick.