pury city multi problem

[gravick]

I am working on a pury-p350ygm-a city multi with 7 indoor units.I am unable to get the discharge pipe to the bc higher than 21c. Have tried to pump down unit but suction stays at 100 psi, when running dischsrge pressure 150 psi. Also I can hear that a bypass has operated. Have tried mitsi help line but they are a bit vague, could be the compressor?
Does anyone have a service manual for this range of unit please.

[stufus]

The bypass is opening to keep the back pressure up.
You need to throw the dip switches to let the unit know you're trying to pump it down
Check the discharge pipe temp at the comp.
YGM-A is R410A those pressures are way to low ,It's short of gas ,you've got a leak
Closest manual I've got
https://rapidshare.com/files/6916766..._HWE10050_.pdf
Cheers
Stu

[gravick]

stufus thanks for your advice. I thought it was low on refrigerant and have added 3kg of 410a but it made no difference to the pressures hence the reason I contacted mitsi.I have tried just operating 1 small unit in the hope that the pressure would rise a little but to no avail.

[install monkey]

can u check on the dipswitches to see if accumulator is reading 0-sog 1 ok 2 overcharge
degas the system weigh and compare to the total system charge-otherwise do the charge calculation by measuring the pipework etc-

[The Viking]

As IM said, the only way to check the charge on these beasts are by reclaiming it and weighing it.

Without knowing the layout of your system...
The total charge might be over 30kg and the system is really good at hiding that it is short of charge so it probably lost somewhere around 2/3 of the charge before you noticed it. +3kg in that situation will not change things much.

So Sorry but it's time to get the reclaim out



.

[gravick]

Thanks for your advice, have been back to site today and checked for leaks with a sniffer at all of the obvious joints that I can see,who knows how many joints could be in the pipework, added more refrigerant in desperate attempt to see if it made a difference. Disconnected the by-pass valve and pressure on dischage rises to 260psi then drops back to 220 and you can hear a by-pass which I think is in the compressor and suction never alters from 100 psi.As you say it is time to suck the baby dry and see what is in there.

[stufus]

The bypass you can still here is most likely the oil return .
Been working on these since they were introduced to the market and have never come across an internal valve failure in a compressor.
But as they say "there's a first time for everything"
Keep us posted
Cheers
Stu

[Thermatech]

If its SOG then you will have excessive discharge temp with low discharge pressure

When you have confirmed correct refrigerant charge run the system in test heat & then test cool & carefully trace the hot gas as is passes through the 4WRV solenoid valves & check valves.
Use 2 sets of gauges one set on the service valve the other set on the LP & HP service ports.
Use the refrigerant pipe layout diagram in the service maunal to confirm hot gas flow route.
If there is a hp to lp bypass this meathod will identify it

[Thermatech]

I have only seen 2 City multi compressors not pumping in nearly 20 years working with these systems so its very rare but not impossible.
After you have confirmed correct refrigerant charge if you still think its the compressor then try running in test heat & confirm the hot gas route through 4WRV through to the service valve. Then shut the valve.
If the compressor is ok it will go straight to very high pressure & trip on hp safety switch.
If the compressor will not pump it will carry on running with no increase in discharge pressure.
Then if you cannot detect the hot gas going any other place in the outdoor unit then you have to assume it is the compressor not pumping.

It always best to try to eliminate any other possible cause as the compressor is expensive & if you change it only to find the system still has the same problem then its an expensive mistake & a lost customer.

[gravick]

Thermatech,thanks for your advice, You have hit on one of my problems,no manual and am unable to find anyone with one for this model.
I am checking refrigerant charge tomorrow and hopefully by wednesday will have a better idea of the problems with this unit.This is a system we have inherited and do not know the full history if any work done or faults.
Wil keep you all updated with progtress and thanks again to all of you who have added to this thread.

[bigrac]

just a quick thought before recovering gas. have you knocked all the indoors off for 10-15 mins , then checked lp hp and bc box transducers all reading same as gauges? only ask cause i found hp transducer 5 bar out of cal and lp 3 bar out of cal on same unit last year causing compressor to ramp down, making it look sog. new transducers easy to change... dont have to reclaim.

[gravick]

To all you helpful engineers, have reclaimed all of the gas and found it short of charge. Service valves don`t hold so suspect their has been a problem with this unit since day 1. Have recharged system and everything is now working fine. Left customer complaining that it is too hot and have had to open the windows. They don`t like to use it on cooling!
Once again thanks for your comments