old r22 mitsibushi vrf... is it gas or compressor?

[Improver]

Hi guys i'm having a problem with a a mitsibushi vrf purt200ymf this is serving 2x f.c.u's and 2 x cassettes (aint got model numbers to hand sorry). I'm wondering weither the compressor has lost it's capacity pump the gas round the circuit or it's short of gas.

I had all 4 units on test cooling and found high side pressure 7-8 bar low side 4 bar, 1st f.c.u off b.c box seems to heat n cool nice but others are very very poor when I turn units 1,2,3 off no. 4 doesn't improve.

A bit of history about the system... recently been p.t and regassed about 2-3 weeks ago and found controller missing for 1 x cassette returned to site to wire new controller but found controller above the ceiling still connected to the unit. anyways powered the system down mounted controller on wall and reset system, then thought the unit wouldn't heat/cool due to address issue but found that ok then went about disconnecting everything on cn32 (timeclock) to do a virgin restart this still didn't work.

I then looked at the gas pressures......I think iv'e been on a wild goose chase and the issue is either the comp or s.o.g. any thoughts guys? shall i just pull gas out to see where i am with it?

[Hobair]

Hi it sounds like its short of refrigerant and the further indoor units are being starved of refrigerant and the nearer one is still getting enough, your high side pressure is low, before you go down that route check your compressor is pumping correctly i don't know what model unit you are working on, are there any service valves on the compressor or any way of pumping the system down? So you could then check the compressor.

Regards Paul.

[stufus]

Where are you checking your pressures ,isolating valve connections or service valves?
You need to check pressures at the service connections that are mounted on the crossbar beside the electrical connections box.
Carry out an LEV reset on all units before degassing it.
If it has recently been PT'D there should be a log to confirm results and system charge.
Measure liquid line and calculate additional charge (add factory charge ) and compare.
What's the compressor discharge pipe temperature? about 100c= more than likely undercharged.
Cheers

Stu

[Improver]

I checked pressures at service ports, also i found discharge temp went as high as 92 degrees and for the 2 hrs it was on test cooling it settled to about 66 degrees.

Stufus when you say do a lev reset do you mean power down b.c box to do this? because i have been powering the system down and back up in a sequence indoor units on outdoor unit on b.c box on. Am I resetting the lev every time by doing this?

Hobair I know when a compressor is locked or down to earth but i don't know how to confirm if the compressor has lost its duty to pump gas round. How would I go about doing this? would i shut off liquid line and see if it pumps down?

[stufus]

To do an lev reset on each indoor power down the unit in question and pull the m-net connection ,power back up and wait 3mins,power down and reconnect the m-net then power back up.
A system that age is bound to have a few lev's out of step ,so resetting them is just for piece of mind before pulling the charge out.
Is the bypass valve on the outdoor staying open when its running
Cheers
Stu

[Improver]

UPDATE... returned to site today carried out lev reset to no avail, ran sytem in test cool and found pressures to be 12 bar high( not 7-8 bar which i got before on test cool which is a bit confusing) 4.5 low. On test heat i got 18 bar high side 6 bar low side.

I concentrated on the b.c box and found all solenoids energised as requested by controllers but only sv1 allowed gas through. swapped good s.v's over from no. 1 to no. 2 and found only sv1 allowed gas through again ruling out faulty sv coil.

So i and another, a.c engineer now feel that it is the actual valve housing that is at fault so we are going to replace it if parts are still available unit installed 1996.

Any further advise or input would be apprieciated. thanks for your input so far anyways lads.

[moondawn]

To do an lev reset on each indoor power down the unit in question and pull the m-net connection ,power back up and wait 3mins,power down and reconnect the m-net then power back up.
A system that age is bound to have a few lev's out of step

Hi stufus after doing this would you require resetting the oc?

[stufus]

Where have you been hiding mate ,been a bit quite lately,
I suppose your settling down for the match.
Procedure is the same for bc , no need to reset the outdoor although it won't do any harm.
The most common LEV failure is LEV 3 in the BC.
Cheers
Stu

To do an lev reset on each indoor power down the unit in question and pull the m-net connection ,power back up and wait 3mins,power down and reconnect the m-net then power back up.
A system that age is bound to have a few lev's out of step

Hi stufus after doing this would you require resetting the oc?

[moondawn]

hi stufus see pm mate.

cheers if there is no need to switch OC off that will do for me epescially if its 3 floors up and im on the ground floor ac unit.!!

cheers

[JoeAT50A]

If OC power switch off, OC will start doing initialization for 45 mins (estimated) for 200 model.
During this initialization time, you found it difficult to judge TH1 (compressor discharged temperature) and as well as compressor speed. (Anyway all will reset during initialization)
However (for cooling), Tc should be reached around 54C. and Te should be around 5C: TH1 should be 107C. Condense outlet temperature TH5 should be around 50C.
For heating
Tc = 50C, Te= -3C and TH1=100C and TH5=-2C
If SOG, run cooling mode to make refrigerant adjustment via looking at BC controller's sub-cooling (inlet and outlet).

[Improver]

thanks joe for input ill check for those temps, but just when i think im winning with this job im back at square 1 again. When talking to mitsibushi tech today i told them i think the b.c box is not allow gas through they said they have never had the actual "block" in b.c box fail.

They think it's either system 1 l.e.v sticking open or the other 3 lev's on the other 3 units stuck closed, even though i done an l.e.v reset they may be mechanically stuck.

So going back to site to run system 1 in fan only mode and take 3 lev's off this will then release the mechanism to allow gas through.

If this fails and i cannot confidently diagnose the fault then out..... comes my hammer!!!!! lol

[install monkey]

if your taking lev heads off use 2 open ended spanners as they are on tight and the plastic head can become brittle with the heat, do the 2 ducted units first-the cassette lev heads can be removed via the access panel where the pipework goes into the cassette-about 4 inch sq- probably best to just slacken the heads as opposed to removing them completly-reason being they are a pain in the arse to compress the pin to allow the nut to bite-on a cassette u will have to strip the facia cover off(after supporting/removing the ceiling tiles and t bar-drop the electrics,drip tray and fan blade to then remove the access panel for the lift pump-good luck

[Improver]

thanks install monkey for your input i can tell you have had to do this before lol, yeah it seems a bit of a headache of a job but it's got to be done never had to do this before so it's a learning curve for me. I've spent so long on this job without confidently diagnosing the fault it's fustrating( well wasting time looking at the wrong things). But i do want to get to the bottom of it and hopefully get it back up and running.

Going back to site next monday evening so i'll probably update this thread tuesday evening with my findings... stay tuned folks.

[Improver]

job update if any1 is still interested....IT WAS THE LEV's!!!!!.......... Stripped units down tho expose lev's removed the plastic body, ran units in test heating/cooling and got good temperature differences. Ordered 4 lev's going back to site next week to install hopefully that will be the end of that job.

It's been educational this job ive learnt loads and have a better understanding of the system, if it happens again ill be alot more confident working through it, you never stop learning in this trade.

[install monkey]

nice 1, common prob on old city multi-youll know for next time- tip, just swap the valve heads as its easy to cook the bodies if brazing-thus more problems