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ronaldo9
05-06-2009, 09:42 PM
Hey guys,

Just visited a site today with a mitsubishi vrf system, all indoors are running fine, aside from one unit in particular. The unit does nothin on either heating or cooling. I checked the BC box for any obvious problems (thankfully i can access the box easily) .
I then checked the indoor coil. The liquid line was warm on cooling and the suction warm on heating. However the coil is always at ambient.
I then disconnected the fan to check the coil temp, on cooling the temp of the coil began to drop for about 30 to 40 seconds and then it returns to ambient.
Is there a blockage in the LEV or in the coil?

Ive visited this site before but never working on this system, from what i can gather this unit has never worked since it was installed.

Ive read some other posts with similiar problems (particularly the post from marc5180)but it didnt address my specific problem..

Thanks in advance for your help

A/C MAX
06-06-2009, 12:33 AM
Hi ROnaldo,

One day I have a similar problem, the cause was the fan in the condenser unit, also you can also check for an open circuit in the control wiring to the condenser

Rgds

Thermatech
06-06-2009, 10:27 AM
If the end user thinks the unit never worked then start by looking at the BC port address set at the indoor unit & then trace the refrigeration pipework back to that port at the BC to confirm the BC port address at the indoor unit is correct.

At commissioning each indoor unit has to be told with an address setting which BC port it is connected to so that it can request cooling or heating refrigerant flow from that port at the BC box.
But
If the refrigeration pipework is actually connected to another port at the box or an unused port then the indoor unit will not get refrigerant flow.

The BC box port solenoids only open / shut the suction gas & hot gas for cooling / heating refrigerant flow.
The liquid line is always live to each indoor units, there are no liquid line valves in the BC box.

If are sure that the BC port address at the indoor unit is correct & you get some small cooing at the indoor unit for 30 seconds then check the solenoid coils are operating for that BC port to open the gas side for refrigerant flow.

If you are sure the BC port address & BC port solenoid valves are operating correctly then try the LEV valve at the indoor unit.
Put the unit in test cool.
As you un screw the motor head from the valve body you are effectively opening the neadle valve manually.
If you completely remove the motor head from the valve body the LEV will be 100% open but for max cooling only about 25% open is required so no need to completly remove motor head just un screw a few turns.
If you get good cooling performance then replace the LEV valve motor head.
If still no cooling you have to suspect liquid line strainers are blocked which requires refrigerant recovery & blow ofn through the indoor coil to prove.

BTW
When the install engineer makes wiring connections its easy to disturb the LEV valve wiring connection at the indoor circuit board so make sure its plugged in properly.

ronaldo9
06-06-2009, 01:18 PM
Sorry i should have said that there was no error codes showing up..

Condensing fan seems to be running ok, ill check for any open circuits.

Thanks Thermatech for a very comprehensive answer, very helpful as im not familiar with Mitsubishi BC boxes and their operations. Didnt realise the liquid line is always live, i checked the pipes to make sure they werent mixed up with any other units, there werent. However the port address thing sounds like a serious possibility. ill be back on site some time next week so ill check all your suggestions.

ronaldo9
10-06-2009, 09:09 PM
Sorry guys,got this completly wrong, was back on site today, i was alone. Basically when i asked the guy working with me the last day to check the rest of the indoor units, he said they were all working fine and nobody was complaining. I took his word for it. My mistake i should have checked them myself. Anyway even though nobody else in the office block complained about their A/C, the entire system is not performing.

In cooling no coil temp goes below 10 deg, it would seem the system is SOG, but when i had all units in test mode the suction of the outdoor unit was cold (the liquid line was hot?????) Mitsubishi tech said that should indicate adequate refrigerant. im at a loss without a service manual, The outdoor is a PURY-P500YGMA i tried to register in mitsubishi website with no response.

marc5180
10-06-2009, 10:33 PM
I would put 2 maybe 3 of the indoor units on test cooling and check if you are getting any cooling.

If you put all of the indoors on test when the system is SOG you will often get the temperatures you describe.

Have you put your gauges on to look at the pressures?
Do you know how much refrigerant the system holds?

I personally would recover the refrigerant to be sure the correct charge is in the system and if it is then you can start to look at solonoids not opening, LEV's shut, Wrong Port address etc etc.

Send me an email and i will send you the service manual.

Brian_UK
10-06-2009, 10:43 PM
One thing also with putting all units on; if there is diversity in the system then it will not perform as you expect.

ronaldo9
10-06-2009, 10:50 PM
Hey Marc5180, thanks for the reply,

The suction pressure is around 10 bar when all units are in cooling.
The units seem to perform the same regardless of how many are on. Havent checked factory charge but there is a sticker saying additional charge of 25kg. Im reluctant to recover refrigerant as the office manager believes a bad system is better than no system. However as marc5180 said check charge first and then i can worry aout solenoids etc...

ronaldo9
10-06-2009, 10:52 PM
Hi BrianUK,,

Just wondering what you mean by diversity,,, heat/ cooling or different indoor models ? not all indoors are the same

marc5180
11-06-2009, 04:47 PM
Im reluctant to recover refrigerant as the office manager believes a bad system is better than no system.

He wouldn't say that if he realised that the compressor could be getting less suction vapour back to cool the compressor which could cause the compressor to burn out due to overheat:eek:

Thermatech
11-06-2009, 07:13 PM
If the total of all the indoor unit capacity added up = more than the outdoor unit capacity of 500 then the indoor units cooling will be reduced when all indoor units are reqesting max cooling as the compressor can only ramp up to 100%.

This is the effect of diversity if all indoor units are calling for max performance.

In this case the suction pressure might be slightly high
which seems to be the case as I would expect in our ambient conditions to be running around 8 to 9 bar & you have 10 bar.

but you report hot liquid line at the outdoor unit. What temp ?

If all indoor units are calling for cooling liquid line should only be warm at exit from outdoor condenser coils.

In this case check operation of the outdoor reversing valve. I suspect locked in heating possition.
Fits your description very well
hot liquid line almost no cooling at indoor units & high suction pressure.

To test RV 4w valve
1/ put all indoor units in test heat so the outdoor unit can only run in heat only mode.
2/ with the system running ok in heating mode with good pressure then un plug the 4w rv from the circuit board.
It is energised for heating possition so when unplugged it should instantly change over to cooling mode.

If it does not then if you follow the hot gas through the 4w rv you will find it is going straght to the unit liquid service valve & not to the outdoor condenser coils.

When the warmer weather comes there are always a few like this each year.
I have done at least 3 since early May.

ronaldo9
11-06-2009, 10:30 PM
Thanks Thermatech, a comprehesive answer as always,

Recovered refrigerant today, no loss the charge was spot on. 22kg factory charge plus another 24.6kg field charge.
Ive been trying to get someone with Mitsubishi service tool to check system , hopefully i have a guy coming sometime tomorrow to check it over. Its very difficult not to mention frustrating trying to troubleshoot with no error code and limited information. I did however get a manual which came in handy as i was able to see some of the information the service tool would provide on the outdoor PCB segment display. Here is some of the information i got when i had;
All 6 units from a sub BC Box on cooling and
2 units from the master BC box on cooling

BC Main
TH11 = 2.1
TH12 = -3.6
TH15 = -2.6
TH16 = 11.5
PS1 = 18.2
PS3 16.3
LEV1 = 2000
LEV2 = 476(went up to 2000 when i took 2nd reading)
LEV3 = 2000

BC Sub
TH12 = 23.6
TH15 = 19.7
LEV3 = 60

I thought it was strange that LEV1 + 3 on main BC box were fully open.
After getting these readings i decided to do a virgin restart, just to reset everything in case LEVs were locked open or something. When i started system back up i put just one unit on cooling. This unit worked fine coil temp got down to -3. Started a second unit same story unit performed well. However when i started the third unit the performance really suffered and nothing worked.:(

Im interested in what you said Thermatech about the liquid line being hot. I would have thought the liquid line from the outdoor unit to the BC box would be slightly subcooled but its RED hot at times. Ive mentioned this to anyone ive contacted about the system and they've assured me that its fine. The head pressure is around 25 bar. Just wondering wots the solution if 4 way valve is locked?
Another thing is there seems to be a slight knocking noise from outdoor unit?

BTW really appreciated the feedback guys, this place is a god-send

moondawn
12-06-2009, 01:43 PM
hi there its not something silly like the two pipes are mixed up at the condensor end ie liquid pipe size could be the same as the suction pipe size and could have been crossed.

just a thought i have seen this once on a system where both the liquid and suction pipes were inch and 3/8 for example and had been crossed by accident. none of the indoors would cool or do anything.

marc5180
12-06-2009, 04:03 PM
From what i remember the suction is 1" 1/8th and the liquid is 3/4 so it would be pretty difficult to mix these up.

marc5180
12-06-2009, 04:13 PM
When i started system back up i put just one unit on cooling. This unit worked fine coil temp got down to -3. Started a second unit same story unit performed well. However when i started the third unit the performance really suffered and nothing worked

If the 4 way valve was locked in heating possition then you would be getting no cooling at any of the indoor units like you say you are.
Have you tested the 4 way Valve like Thermatech suggested?



Im interested in what you said Thermatech about the liquid line being hot. I would have thought the liquid line from the outdoor unit to the BC box would be slightly subcooled but its RED hot at times. Ive mentioned this to anyone ive contacted about the system and they've assured me that its fine.
Did you take the temperatue of the liquid line? this should prove if infact the 4 way valve is locked in heating and you could check the subcooling leaving the receiver/condensor.


Just wondering wots the solution if 4 way valve is locked?

The 4 way valve will need replacing if it turns out the valve is seized.

Thermatech
12-06-2009, 09:44 PM
If the 4w rv was locked in heat possition you would not get good cooling at any indoor units

But it could be locked at any possition between cooling & heating so you need to check pipe temps at the 4w rv to be sure.

Now you have some more data it would seem you have strainge data at both BC boxes.
The master box will only open LEV 3 to max 2000 if not making target subcool. So fully open is sure indication of refrigerant flow problem.
The outdoor unit shows 25 bar discharge but only 18 bar inlet at the master BC. what happened to the other 7 bar?
Thats a lot more than the pressure drop on a very long pipe run.
Is LEV 3 on slave box only closed at 60 due to the indoor units connected to it being at off ?

Refrigerant flow is not right at some place in the system or some incorrect data from temp or pressure sensors because you have now proved that refrigerant charge is correct.

If you were in UK I would offer to come with Mnet monitor computer & trouble shoot this for you but IRL means return flight from BIR or east midlands which makes excessive cost for you.

BTW the indoor coil temp at -3 ? this should be more than +1 or the indoor units goes to coil frost prevention after about 5 mins.
Any indoor coil temp below +1 is a problem unless the indoor units is operating at indoor unit room temp below 15 deg C WB for instance in computer room application.

moondawn
13-06-2009, 09:21 AM
If the 4w rv was locked in heat possition you would not get good cooling at any indoor units

But it could be locked at any possition between cooling & heating so you need to check pipe temps at the 4w rv to be sure.

Now you have some more data it would seem you have strainge data at both BC boxes.
The master box will only open LEV 3 to max 2000 if not making target subcool. So fully open is sure indication of refrigerant flow problem.
The outdoor unit shows 25 bar discharge but only 18 bar inlet at the master BC. what happened to the other 7 bar?
Thats a lot more than the pressure drop on a very long pipe run.
Is LEV 3 on slave box only closed at 60 due to the indoor units connected to it being at off ?

Refrigerant flow is not right at some place in the system or some incorrect data from temp or pressure sensors because you have now proved that refrigerant charge is correct.

If you were in UK I would offer to come with Mnet monitor computer & trouble shoot this for you but IRL means return flight from BIR or east midlands which makes excessive cost for you.

BTW the indoor coil temp at -3 ? this should be more than +1 or the indoor units goes to coil frost prevention after about 5 mins.
Any indoor coil temp below +1 is a problem unless the indoor units is operating at indoor unit room temp below 15 deg C WB for instance in computer room application.


Always Love reading your posts thermatech very comprehensive and make it really easy to understand.

thank you;)

ronaldo9
03-09-2009, 08:31 PM
Hey guys,

i apologise for not posting for so long, sadily this situation has yet to be resolved. We got a mitsubishi tech in for a site visit a while ago. (really sound guy). he hooked up his service tool and took a really good look at the system. He made some recommendations such as about replacing an LEV on one of the indoors he felt was passing refrigerant. Another one was to replace the two LEVs on the BC box i.e LEV2 and LEV3. Carried out these recommendations with no luck.
The only good news , if you could call it that, is that there is an almost identical system on the ground floor of this building. This system seemed to be performing in the same sort of manner only slightly better. I started to think maybe these problems are the result of a bad install. I do know that the client wasnt happy with the company that carried out the work. Maybe this is just me clutching at straws. Even though we havent had any complaints since our last visit when we carried out the recommendations, i know the system still isnt right and would have liked to get to the bottom of it. Anyway thanks all for your assistance, especially Thermatech, you should write a book mate, seriously.

marc5180
03-09-2009, 09:20 PM
Thanks for updating the thread, i was wondering what had happened with it.

Sorry to hear it isn't sorted yet but when it is, let us know what it was.

It wouldn't surprise me if the additional refrigerant has been worked out wrong if the guys who installed it were cowboys.

ronaldo9
12-01-2010, 08:53 PM
Hey Guys,


Its been a while but i have good news. I found out what the problem was, the LP sensor on the outdoor unit "63LS" was around 3-4 bar off the actual reading.

Fitted a new sensor and system is working fine. Thank God.

Just a couple of observations:

--You CANNOT fault find these systems without some manufacturer training, i didnt and i had to learn the hard way. The only good thing is that im a lot more confident about working on City Multi systems.
--Why wasnt this spotted with the service tool, i had 3 guys look at this system.
--Ive worked on a lot of Hitachi stuff, Set Free, Utopia etc and never seen this kind of thing where a sensor is off so much, im not saying Hitachi is better than Mitsu but its strange.

Thanks for all the advice and help
Cheers

marc5180
12-01-2010, 09:29 PM
Thanks for updating the thread Ronaldo9.

Recently i've had quite a few problems where the pressure sensors reading the wrong data, on both high and low side.

Now it is one of the first things i check if ever i have a problem.

Thermatech
12-01-2010, 09:41 PM
Thanks for the update

Sometimes if suspect one of the pressure sensors I carry out a standing pressure test by switch off all indoor units & make full pressure equalistation by gauge manifold HP to LP or electronically open the LEV valves at the BC box with Mnet monitor tool.
Then monitor all the pressure sensor data from the outdoor unit & BC box to make sure they all read the same equalized pressure.

With the outdoor unit at least you can compare with manifold gauge on HP & LP & display the pressure sensor data on the outdoor unit circuit board with SW1 data display setting to confirm pressure sensor data is correct.

The system may not trip on any fault but will trim operation to the incorrect pressure sensor data.

The pressure sensor is just a tranducer which takes 5v dc from the circuit board & returns a variable voltage depending on the pressure & the circuit board measures the return voltage & converts to a pressure data reading. So the best test is to display the live data on the outdoor circuit board & confirm correct with gauge manifold reading.